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Jamie
11-22-2008, 06:44 PM
I'm at my wit's end. When I first flew my airplane last year it left the ground with a Trio EzPilot installed. For whatever reason I was never able to get the Trio to work right. In spite of everything I tried, the thing would just not track smoothly. I was using the SafeAir1 mounting kit with the servo mounted in the last bay of the right wing and a long pushrod connected from the servo to the aileron bellcrank. Anyway, I tried everything -- new servo, new head, wiring, etc. I have detailed this issue on other theads here on VAF, but I discuss it here only for back story, nothing else. I don't blame Trio for this issue, they tried to help, but there's only so much they can do remotely and so many dollars in avgas I can spend before I just gave up. I just sat down and added up the cost for me. It was > $500.00 in avgas diagnosing that Trio problem and I never came up with a solution. That $500.00 figure only includes flights specifically made to try new things with the Trio.

Well, as mentioned I gave up. When Dynon announced their autopilot I thought I would give it a try. I liked their ideas with their AP and I've been a happy customer with their EFIS and EMS in my panel.

I installed their autopilot (two-axis). The roll axis is perfect. It tracks extremely well. The only thing I don't understand is why when you tell it to fly a GPS ground track (i.e you set a track on the Dynon), it overshoots it every time. It doesn't make much sense to me. I also have an issue with the Dynon occasionally barking at me about losing the GPS signal and defaulting to magnetic heading mode. I never lose the HSI and if I go to the AP menu I can re-enable the NAV mode (so it tracks the GPS) with no problem. I've only done preliminary testing with this issue so for me this is lower priority.

The other thing (this is my big problem) is that the Dynon altitude hold is behaving badly. Tweaking the sensitivity settings, the best I can get the altitude hold to perform is +- 20 feet. I engage the altitude hold with the airplane trimmed and it will hold for about one minute or so and then begin an oscillation. The oscillation will grow larger and larger until it maxes at +-20 feet in altitude, but about +- 600fpm in rate. This is with the Dynon sensitivity setting set to the maximum value (25).

I pressure checked my static system and found no leaks.

I vented the Dynon static system to cabin air to ensure that I didn't have any fluctuations in my static system.

I flew the plane from 110kts to 170kts in increments of 10 knots, testing each speed to see if the pitch servo performed better or worse depending upon speed. The speed made little difference.

I pulled the baggage wall and noticed a little play in the mount. In other words, if I engaged the servo, then pushed/pulled on the pushrod until the servo slipped, I would see a little left/right (perpendicular to arm throw) flexing of the mount at the bottom. According to Dynon, the little flange on the bottom of the mount is optional. It's intended to be riveted to the floor. My plane is painted so I wanted to avoid putting drilling through the outter skins and risking chipping paint, etc, so I cut the flange off. In order to stop the flexing I put another fastener in the bottom of the mount. Now the mount is very rigid.

The Dynon support folks are fantastic and are helping me with this issue. Of course I understand that it is a new product and it will suffer growing pains. I fully expect to have some issues, but I'm truly at my wit's end and I'm beginning to believe that it was just never meant for me to have a functional autopilot in my airplane.

I spent all day today on this issue and I finished the day 20 gallons of avgas less, 8 hours without seeing my son and still no answer.

I basically wanted to post here at VAF to see if anyone has any ideas of what could possibly be causing this issue. Also, I know that there are a few Dynon AP beta testers here on VAF so I'm looking to them for ideas.

So, VAF...what say you. :confused: Where should I go from here?

Brantel
11-22-2008, 07:07 PM
I installed their autopilot (two-axis). The roll axis is perfect. It tracks extremely well. The only thing I don't understand is why when you tell it to fly a GPS course (i.e you set a course on the Dynon), it overshoots it every time.

Jamie,

On this issue are you talking about it overflying waypoints when you are going from one waypoint to another and then another or are you talking about it zigzagging one side or the other of a straight course line?

Unless you have a GPS connected that supports GPS steering over ARINC, the GPS will overfly waypoints and then turn back to the course line but I am not sure this is what your talking about.

If your talking about it overshooting when joining a course, maybe you can increase the gain a little at a time to compensate.

Jamie
11-22-2008, 07:18 PM
Jamie,

On this issue are you talking about it overflying waypoints when you are going from one waypoint to another and then another or are you talking about it zigzagging one side or the other of a straight course line?

Unless you have a GPS connected that supports GPS steering over ARINC, the GPS will overfly waypoints and then turn back to the course line but I am not sure this is what your talking about.

If your talking about it overshooting when joining a course, maybe you can increase the gain a little at a time to compensate.

Nope, I've very well aware of GPSS, but I mis-spoke (mis-typed?) my original post when I said course instead of track. The dynon overshoots the ground track. So if you're flying a ground track of 090 and you tell it to turn to 010, it will overshoot 010. That's what doesn't make sense to me.

The Dynon doesn't have gain...it has 'sensitivity', vertical speed limit, min ias and max ias, and servo torque % and that's it.

I've tried every sensitivity setting from 1-25.

N941WR
11-22-2008, 07:35 PM
... I also have an issue with the Dynon occasionally barking at me about losing the GPS signal and defaulting to magnetic heading mode. I never lose the HSI and if I go to the AP menu I can re-enable the NAV mode (so it tracks the GPS) with no problem. I've only done preliminary testing with this issue so for me this is lower priority.
Jamie,

I'll answer this as I was one of the beta testers who found this problem.

This has nothing to do with the Dynon, the Garmin handheld GPS's (and maybe some others) stops putting out a course signal every now and then. When this happens the AP has to switch to heading mode and it is good that the Dynon lets you know this happens, IMHO.

The other thing (this is my big problem) is that the Dynon altitude hold is behaving badly....

I pulled the baggage wall and noticed a little play in the mount. In other words, if I engaged the servo, then pushed/pulled on the pushrod until the servo slipped, I would see a little left/right (perpendicular to arm throw) flexing of the mount at the bottom. According to Dynon, the little flange on the bottom of the mount is optional. It's intended to be riveted to the floor. My plane is painted so I wanted to avoid putting drilling through the outter skins and risking chipping paint, etc, so I cut the flange off. In order to stop the flexing I put another fastener in the bottom of the mount. Now the mount is very rigid....

So, VAF...what say you. :confused: Where should I go from here?
Did you get a chance to fly after securing the pitch servo bracket? Your post wasn't clear to me. It has to be very solid to keep the servo from moving and hunting altitude.

Also, how bumpy was it? This has a real impact on how well this or any autopilot performs.

PS. Check your PM's

Brantel
11-22-2008, 08:03 PM
Nope, I've very well aware of GPSS, but I mis-spoke (mis-typed?) my original post when I said course instead of track. The dynon overshoots the ground track. So if you're flying a ground track of 090 and you tell it to turn to 010, it will overshoot 010. That's what doesn't make sense to me.

The Dynon doesn't have gain...it has 'sensitivity', vertical speed limit, min ias and max ias, and servo torque % and that's it.

I've tried every sensitivity setting from 1-25.

Does it always overshoot the same amount in either direction?

Does it ever come back to the desired track? If so, does it do it quickly or does it wonder around and eventually get there?

If it is a software bug, I bet they will fix it in short order. I wonder if any of the beta testers saw this behavior???


On the Alt hold issue...Just looking for reasons it might do this. Have you flown since stiffening the bracket? Is there anything you notice about your airplane when hand flying it that makes it hard for you to hand fly a fixed altitude? Any slight binding or dead zones with the elevator right at the sweet spot? Any slop whatsoever in your control linkages (have someone hold the elevator and check for slop at the stick).

If your sure about all of these things, then maybe Dynon has some more tweaking to do to their algorithms...

Jamie
11-22-2008, 08:32 PM
I should have clarified -- yep, I've flown since stiffening the bracket.

There is no noticeable drag or slop in the controls. The only noticeable slop is minute -- it's in the bearings which is typical for RVs. The only drag on the elevators is the drag created by the servo itself.

When I engage the servo on the ground it will 'wiggle' the arm a little bit...but it's really not a noticeable amount -- you hear it but you really can't see it. Bill, are you experiencing this?

N941WR
11-22-2008, 09:24 PM
...When I engage the servo on the ground it will 'wiggle' the arm a little bit...but it's really not a noticeable amount -- you hear it but you really can't see it. Bill, are you experiencing this?
Yes, this is normal. The idea is to let you know the AP is working but it should keep you from taking off with the AP turned on.

When you get back to the plane tomorrow, have it run the servo test again just to make sure everything is working as it should before you go fly.

dynonsupport
11-22-2008, 09:53 PM
Jamie,
Have you checked your CG recently? A very rearward CG makes for a plane with almost no pitch stability, and that's the only situation we've had in testing where a plane acts like yours does.

Also, are you getting any slip indications or out of trim indications? If you aren't, can you make them happen manually?

Have you been able to fly with the datalogger turned on? Sending us that data would be very helpful.

I know this must be really frustrating for you, but there's got to be something in your install, airframe, or something broken that is unique. We've got the AP working quite well in a bunch of RV's (and other planes). None of them have this issue. We'll do everything we can to figure this out.

SportAvServ
11-22-2008, 10:06 PM
I'm not an electronic wizard like most of you, but a friend had one of the inexpensive auto pilots and it would wander side to side of the course or heading. We would trim the plane out on heading (RV-6) with the aileron spring trim (works awesome!) then turn on the AP. It would slowly hunt right and left, basically staying on course, but irritating. I thought that once it was on course and in a neutral position it had to wait for a deviation to correct it. We merely put a very small amount of trim to one side, the plane wanted to go one way and the AP wanted to go the other, it steadied up and flew straight. After all that, I'm wondering if it would work in altitude hold, get to your desired altitude, turn on the alt hold and trim up just a little. Just another reason to burn 100LL.

Let me know

RT

N661DJ
11-23-2008, 04:34 AM
I had a similar pitch problem with a Glasair and STech. AP. A friend of mine, a KC135 pilot flew the airplane and said that it "felt a little tail heavy". He mentioned that when they would setup to refule an airplane, they would transfer large amoults of fuel fwrd. in the KC135, making the plane much more stable. The CG calc. were right where they should have been in the Glasair. In an effort to solve the issue, I removed the battery, a Gill G35 from behind the seat, and installed a G25 on the firewall. Problem solved, the AP worked great.
Dick

Jamie
11-23-2008, 05:30 AM
Thanks, Dynonsupport for your weekend response!

Jamie,
Have you checked your CG recently? A very rearward CG makes for a plane with almost no pitch stability, and that's the only situation we've had in testing where a plane acts like yours does.


I did not check my CG after installing the AP, but if anything my CG is on the forward end. I have a Hartzell C/S prop, firewall mounted battery, etc. The only thing mounted aft of the baggage wall is the AP servo, my ELT and the Dynon remote compass (weighs almost nothing as you know). I have hand flown the airplane to and from OSH and several other long trips with 100lbs in the baggage area and the airplane was very pitch stable. An aft CG condition is something that should be immediately apparent to the pilot.

Maybe it's a forward CG issue? I will put some ballast in the baggage area and give it another try.

When I get my fuel tanks burned down low I will drain the remainder of fuel and perform a new W&B. Again, I seriously doubt this is an issue, but I will do a full W&B just to eliminate that possibility.

Jamie,
Also, are you getting any slip indications or out of trim indications? If you aren't, can you make them happen manually?


I trim the airplane before I engage the autopilot. I don't see any out of trim indications until the oscillations reach their 'peak', meaning that at the top of the oscillations I will see a 'down' trim indication and at the bottom I will see an 'up' indication. With the settings I have dialed in now, I don't see the servo slipping. Should I? I'm using a torque setting of 100%. I've been told that my allowing the servo to slip a little it actually smooths out the ride.

Jamie,
Have you been able to fly with the datalogger turned on? Sending us that data would be very helpful.


Yes, the datalogger was turned on all day yesterday. Not sure how much it got, but hopefully it will have the data from the last flight. I neglected to bring my laptop to the airport yesterday so I will go out today and download the datalog.


I know this must be really frustrating for you, but there's got to be something in your install, airframe, or something broken that is unique. We've got the AP working quite well in a bunch of RV's (and other planes). None of them have this issue. We'll do everything we can to figure this out.


Have any other RVs installed the altitude hold and cut the flange off the bottom of the mounting bracket? That's the only thing I've done a little differently.

Yes, it has been very frustrating and please believe me when I say I'm not taking it out on you guys.

One thing I don't understand about the AP, if I'm 10 feet below the target altitude, it will try to correct at about 300fpm and shoot right through the target. The VSI as displayed on my EFIS is extremely precise. In other words, when hand flying you nudge the stick a little forward or backward and you will see the VSI on the EFIS change before either altimeter (EFIS or standby) really sees any change. It's fairly high resolution. So why does the AP seeing the target altitude coming, seeing that it's climbing at 300fpm...why does it shoot through it. It doesn't start pitching forward until it's already passed the target. The same thing happens on the downline. It goes right through the target. It's like the pitch is held constant until the moment it hits the target. By then it's too late.

Jamie
11-23-2008, 05:35 AM
I had a similar pitch problem with a Glasair and STech. AP. A friend of mine, a KC135 pilot flew the airplane and said that it "felt a little tail heavy". He mentioned that when they would setup to refule an airplane, they would transfer large amoults of fuel fwrd. in the KC135, making the plane much more stable. The CG calc. were right where they should have been in the Glasair. In an effort to solve the issue, I removed the battery, a Gill G35 from behind the seat, and installed a G25 on the firewall. Problem solved, the AP worked great.
Dick

Thanks, Dick for the info. As mentioned in my previous reply to DynonSupport I will try ballasting the airplane fore and aft. It sounds that like me, you were not able to detect any peculiarities when hand flying. Interesting.

MrNomad
11-23-2008, 08:36 AM
Jamie:

As I said in my other post, I installed the AP74, Dynon servos and connected them to the D100 & D180. My pitch & roll mounts came from TruTrac and were SECURELY mounted during the 18 month build. They have NO play nor movement nor did I drill thru my painted belly to rivet. As my good friend Chet will attest, I tend towards MORE strength and more rivets leaving little or no chance for movement. Zero movement of the bracket is the right amt as far as I'm concerned.

The pitch servo arm attachment was connected at the most distant hole (per specs), 1.50" out. Given its distance from the fulcrum, any movement request issued to the servo will result in greater movement at the control rod versus attachment at 1.25".

The axis of the movement of my pitch servo remains within the radius suggested and is equidistant from both ends of the travel. In other words, assume full movement of the pitch servo arm is N degrees after attachment to the control rod. My arm rotation end travel between final resting point and absolute horizontal equates to 180 - (rotation/2) and is equidistant from both ends of the axis. Movement will not be linear across the full spectrum of movement but both ends of the axis will be alike. IMHO, that's got to be right for the system to work correctly.

Speak to Dynon first, but if you moved the pitch servo arm connection point from 1.50 down to 1.25, each movement of the servo would generate less movement on the rod. Assuming enough travel remained allowing full flap movement without going overcenter (overcenter would result in disaster), that would seem to reduce the servo's impact on the rod but I would not do that w/o Dynon's agreement.

I guess you could also swap servos, re-educate the software to acknowledge the change, and see if the problem travels with the servo. That's a lotta work but the process of elimination might help.

The Dynon manual adds two terms. "Twitch" and "wallow". On flight 1, I found my 9A rocked back and forth as though I was trying to get the tower's attention. I mistakenly thought that was "wallow" so I increased sens from 10 to 20 and the prob got worse. I reduced to 5 (from 20) and that went away.

You indicated that you've tried pitch sens from 1 to 25 so sens is not an issue assuming sens is working right. Surely you detected a difference in performance from 1 to 25. Yes?

Finally, I assume Dynon has some form of checksum which insures that the software upload was successful, but you might confirm that with Mike at tech support. Windows is notorious for bad uploads, but I would hope that Dynon embedded that simple safety factor in their program which ensures that you uploaded with no errors and the copy you downloaded also had no errors.

Last, the GPS option does definitely HUNT. Using GPS, I pointed the AP to a waypoint which had a compass heading of 10 deg from my present hdg which was compass hdg 270. The AP pointed me towards compass hdg 290 and given the mountain I was headed for, I didn't wait for it to correct. I then entered a different waypoint on my Lowrance 2000C. The new waypoint hdg was 60 deg on the compass, the AP redirected and went straight for it like an arrow.

Later on flight 2, I entered a waypoint which was 190 deg. The AP swung the airplane to 220 and then eventually back to 190. On the moving map display of the Lowrance, the little airplane was visably off course but it eventually straightened out. If I recall correctly, the data on the HSI was correct which says to me that the AP does not gradually adjust as the target comes in (it overshoots) but before anyone criticizes I'd like to test that again on flight 3. If the HSI has the right coordinates for trk and hdg, then the issue would seem to be between the D100 and the AP.

If anyone has any thoughts how to reduce that error, lemme know but I won't be taking any naps (haha) till that's resolved.

Finally, one of Dynon's test pilots lives here in Tucson. He's three of the smartest people I ever met and when I see him next, I will happily discuss your issue and my gps question.

Barry RV9A, Superior O-360, Sens Prop, 90hrs in one year.
Tucson

dynonsupport
11-23-2008, 11:09 AM
One thing I don't understand about the AP, if I'm 10 feet below the target altitude, it will try to correct at about 300fpm and shoot right through the target.

Jamie,
I don't have much else to say or mention until we see the datalog, and it sounds like you may have one or two unlikely things to check.

As for why the AP is adjusting so hard when only 10 feet off, let's just say that humans make amazing control systems. You have so much information at hand- airspeed, altitude error, pitch, etc. But even more than that, you have knowledge about how much you care about a 10 foot error, you have infinite resolution when moving the stick, and you have hundreds of hours of training in how to control vehicles.

The AP only has a subset of your info. Clearly, something in that subset is making it think it needs to pitch a lot to fix the 10 foot error. You might know that just means a slight pressure on the stick, but when you do that, you also know via the nerves in you fingertips that you are actually applying that pressure, and you have a whole other set of senses that helps you detect the aircraft is responding. The AP can only look at a few things, apply one tick of motion to the servo, then wait to see if the aircraft responds. Clearly it's overestimating how much it needs to do for some reason.

Anyway, long way of saying that an AP doesn't fly the airplane the way you do or with the info you have. If you can write a control system that is as smart as a human and can learn how to fly an airplane over time, then you will be a very rich man. As technology stands today, we haven't figured out how to be as smart as a person. But we're trying hard, and we appear to do pretty good in most installs.

All of this does bring up one other question: How many degrees does the arm on the servo move over the full range of pitch? Barry kind of mentioned this, but if the servo isn't moving much, then every little input we put into it causes a big response. It's fine to move the arm in on the servo end as long as you don't get anywhere near over center.

You should not need to back off from 100% torque. I was just checking to make sure that all the feedback from the servo appeared to be working.

CozyIV
11-23-2008, 02:06 PM
Could reverse sensing be the problem?
On my instal (TT) because of the position I had the servo arm mounted on the servo the AP senors corrections were applied in reverse. When a climb was sensed it would give the apropriate directions to the servo to return to level flight. However because of the way I had the servo mounted the aircraft climed further. It was a viscious circle, the more it climbed the more the AP sensor comanded it to climb.

Snipping a jumper wire on the AP altitude module forced the the directions that were sent to the servo to be reversed, problem solved.

Just a thought.

MrNomad
11-23-2008, 04:41 PM
Folks at Dynon support, please tell me if this explanation of the AP74 GPS function is correct.

Hypothetically, let's say I'm flying towards zero degrees on the compass. I instruct the GPS to GOTO an airport located at 90 deg. At that precise moment, the C program inside the D100 draws a straight line between where I am and where I want to head. But, because I'm still moving north at 150kts, my actual position is further north by the time the airplane makes the right turn towards 90, and so it heads back (at 110 deg for example) towards the original line that the D100 drew. When it arrives at the line the D100 drew, it turns again towards 90.

Another analogy would be driving on the freeway. Assume you're headed due north driving on the freeway. The car goes off the side of the road by 100 feet. Conceivably, the shortest point to the destination would be a straight line 100 feet off the road and the destination, but logically you wouldn't do that. You'd drive at a right angle back to the paved road, and then turn north on the freeway.

Am I correct? Is that the logic you folks used to program the GOTO GPS function?

If so, allowing the AP to execute a steeper bank angle would reduce the oscillation reqd to get on track. I can also foresee assisting the GPS by hand banking 60 deg (the AP is limited to 35) in a tight Class C circumstance one frequently runs into in the LA area and then allow the AP74 to clean up and head for the final direction.

Thanks for a great product and answering questions on the weekend.

Barry
Tucson

dedgemon
11-23-2008, 04:48 PM
Sure sounds like your gain is too high. You said you're at 25 right. And thats the max "sensitivity" right? Hows it behave at 12 or so?

Dynon Support. I presume that this "sensitivity" is really a loop gain adjustment right?

Bryan Wood
11-23-2008, 04:59 PM
Jamie,

Did you ever vent the static line to the cabin and try the autopilot?

dynonsupport
11-23-2008, 05:44 PM
Jamie did try venting to the cabin.

Reverse sensing is impossible with the Dynon AP unless you lie to it. We don't control polarity with wires like TruTrak does. Once you have the system installed, we ask you to put the stick in the upper left then lower right corner. We detect these positions and figure out what way you have installed the servo. Since we actually know the position of the servo (TruTrak doesn't) there are lots of neat things we can do. We even warn you if it the servo arm moved too far and you're at danger of an over-center situation.

In any case, Jamie's plane does not diverge forever. It's just slow to
respond, but does actually oscillate around the target. A system in reverse would just shoot away and never come back.

I do agree that 25 is way too high for "sensitivity" (which is gain). Most RV's are flying in the 9-15 range. 25 is our max. But Jamie has tried everything from 1 to 25 and feels the performance is best at 25, so clearly something is up.

dynonsupport
11-23-2008, 05:51 PM
Barry,
You're misinterpreting who does "GOTO" in this situation.

We have no idea where we are going. That's your GPS's job. All we do is listen to what the GPS tells us to do. If it says we're left of course, we turn right, and vice versa.

If you say direct to something that is north of you, but you're headed east, the GPS creates a direct course line from where you are NOW to where you want to go. Direct to isn't a continuous function, it's a request for a line at one point in time.

Ever GPS I have ever seen does this. Direct to means create a direct course from where you are now to where you requested. If you're flying perpendicular to that course, you have to turn around and fly back onto it.

All the Dynon sees from the GPS is the exact same thing that is on the HSI. The course heading, and the course deviation. The AP's job is singular. Make the CDI 0 NM. It doesn't know or care where that takes you, or even if the GPS is moving the CDI constantly. Just do what you can to make it 0. We truly have no idea what your waypoints are or when you create them.

If you're having overshoot issues, try fiddling with the sensitivity some more. When it's dialed in it will fly a perfect curve right onto the course.

647jc
11-23-2008, 06:18 PM
Jamie,

You mentioned you originally had a Trio EzPilot installation. I looked at the Trio installation documents and the location of the hole in the bell crank where you connect the Servo linkage is not specified very clearly, they state ?Begin by looking for a point on your elevator bell crank, control pushrod or cable where pushing or pulling the elevator control linkage a distance of 1.5 to 2.4 inches will do the job.? The Dynon installation specifies the hole should be 2.5? from the bell crank pivot axis.

It sounds like your installation is OVER controlling the airplane and this could be caused by the bell crank linkage hole being closer to the axis than the 2.5? Dynon recommends. If that is true you may be able to compensate by using a hole on the Servo arm closer to the Servo shaft but this would result in a loss of torque which may or may not be an issue.

Do you know where the linkage connection hole on your bell crank is located with respect to the bell crank pivot axis?

Jamie
11-23-2008, 07:00 PM
Jamie,

You mentioned you originally had a Trio EzPilot installation. I looked at the Trio installation documents and the location of the hole in the bell crank where you connect the Servo linkage is not specified very clearly, they state ?Begin by looking for a point on your elevator bell crank, control pushrod or cable where pushing or pulling the elevator control linkage a distance of 1.5 to 2.4 inches will do the job.? The Dynon installation specifies the hole should be 2.5? from the bell crank pivot axis.

It sounds like your installation is OVER controlling the airplane and this could be caused by the bell crank linkage hole being closer to the axis than the 2.5? Dynon recommends. If that is true you may be able to compensate by using a hole on the Servo arm closer to the Servo shaft but this would result in a loss of torque which may or may not be an issue.

Do you know where the linkage connection hole on your bell crank is located with respect to the bell crank pivot axis?

Hi Joe:

I did not have the Trio avionics altitude autopilot, only the Trio roll autopilot. When I went with the Dynon I elected to install both roll and pitch. My pitch install is per the Dynon installation instructions. The Dynon and Trutrack installations are physically identical and tonight I had the opportunity to inspect a TT install. I could see nothing different physically from my install.

BrentHumphreys
11-25-2008, 06:37 AM
... let's just say that humans make amazing control systems. You have so much information at hand- airspeed, altitude error, pitch, etc. But even more than that, you have knowledge about how much you care about a 10 foot error, you have infinite resolution when moving the stick, and you have hundreds of hours of training in how to control vehicles.


As a Control systems engineer, I have to disagree. Yes, the human brain is incredible at integrating various kinds of sensory input and determining appropriate control responses. However, there is very little precision, and responses are much slower than an automated control system.


The AP only has a subset of your info. Clearly, something in that subset is making it think it needs to pitch a lot to fix the 10 foot error. You might know that just means a slight pressure on the stick, but when you do that, you also know via the nerves in you fingertips that you are actually applying that pressure, and you have a whole other set of senses that helps you detect the aircraft is responding. The AP can only look at a few things, apply one tick of motion to the servo, then wait to see if the aircraft responds. Clearly it's overestimating how much it needs to do for some reason.


If the AP does not have enough input to control, then that is a design flaw.

If the controller the AP is using does not have enough resolution to control, that is a design flaw. As you state, placement of that control is critical.



... If you can write a control system that is as smart as a human and can learn how to fly an airplane over time, then you will be a very rich man. As technology stands today, we haven't figured out how to be as smart as a person. But we're trying hard, and we appear to do pretty good in most installs.



I don't think an AP has to "Learn" to fly over time. This is simple feedback control. If you are familiar with PID control, it is just a matter of tuning the loops to get proper control.

Ironflight
11-25-2008, 07:54 AM
I don't think an AP has to "Learn" to fly over time. This is simple feedback control. If you are familiar with PID control, it is just a matter of tuning the loops to get proper control.

It's that the humans have to "learn" how to tune the thing - that's what takes the time Brent! I have spent countless ours in simulations and flight testing trying to get automatic flight control systems to fly the way we'd like them to. The design only goes so far - after that, there is a bit of an art to it!

Paul

Rainier Lamers
11-25-2008, 09:14 AM
It's that the humans have to "learn" how to tune the thing - that's what takes the time Brent! I have spent countless ours in simulations and flight testing trying to get automatic flight control systems to fly the way we'd like them to. The design only goes so far - after that, there is a bit of an art to it!

Paul

I was going to stay out of this one, but I can't.
You are absolutely, 100% right.
Learning how an aircraft responds to control input and using limited and noisy sensors that contain unavoidable errors and lag is not as simple as it looks.

Once you are done you will have a lot of "If ... then ... else" stuff in your system, it's definitely not just a simple PID controller. If you're going to implement this using a simple PID feedback system I can guarantee you that you will not be happy with your systems response.

This requires a LOT of fine tuning and a clever idea here and there to get it perfect.

Dynon has my full sympathies on this one and I know that their system will continue to develop as user input starts pouring in and it will be as close to perfection as you can ever get it very soon. Give 'em a chance.

Rainier
CEO MGL Avionics

Pat Hatch
11-25-2008, 10:14 AM
Jamie,
I had the same pitch problem on my RV-6 with a totally unrelated autopilot, an S-TEC 30, and the problem was resolved eventually. I tried everything; I even had S-TEC give me an adjustable gain by providing a rheostat on the pitch computer where I was able to adjust the loop gain in flight. But the problem turned out to be in my static system. I vented the autopilot altitude-hold transducer to the cabin (basically just pulled the static line off) and the problem went away. I think I just had too many items feeding off the static system and it was causing some instability within the autopilot pitch computer in the altitude-hold mode. I know you said you had already vented your altitude-hold transducer to the cabin, but did you re-adjust the gain after you tried this?

allbee
11-25-2008, 10:15 AM
lets try and give a logical look at this. you had problems with another AP in your aircraft, you put in the Dynon and you still have problems. What if, you have something in your aircraft putting out something that's effecting the system. Have you tried turning everything off except the dynon, AP, and gps. I mean even turn off the field for the alt. OF course if it works fine, just start turning things back on.

Jamie
11-25-2008, 10:15 AM
I fully expect Dynon will work through this issue with me until the very end. I feel that a) They realize that I will probably not be the last person to see this issue and b) it's just the right thing to do customer service wise.

Again, I'm not upset with them in the least, just generally frustrated. In fact, I'm more and more impressed with them and their responsiveness and genuine desire to work out this issue. Heck, they even responded to my VAF posts on the weekends.

I have decided that I will meet my frustration with a head-on, methodical approach. One of the neat things about the 5.0 firmware release is they added internal logging to the EFIS (previously you had to bring a laptop, etc. along and capture the data). This data logging will allow me to capture some fairly precise information (1 sec. increments) regarding the flight characteristic of my airplane.

Anyway, I will go up and fly some pitch stability (phugoid) tests and get some good hard data from the Dynon regarding the performance of my aiplane. Then I will engage the Dynon AP and log performance at each sensitivity setting. Hopefully this will give the Dynon guys something to chew on.

In my day job I have done quite a bit of automation work with industrial-type machinery, so I can definately sympathize with them. Once I had a bug in a piece of code that was randomly shooting holes in the side of Coca Cola syrup boxes at a fountain plant. It took me two weeks to find the problem -- so again I can really sympathize. :) Having said that, I don't think the install base is large enough yet to place the blame squarely on the airplane (yet).

Here is the test card that I plan to fly. If anyone has any other tests that may be pertinent for diagnosing this problem I'm all ears.

Test Card (http://www.jpainter.org/archive/AP_Test_Plan.pdf)

Jamie
11-25-2008, 10:25 AM
lets try and give a logical look at this. you had problems with another AP in your aircraft, you put in the Dynon and you still have problems. What if, you have something in your aircraft putting out something that's effecting the system. Have you tried turning everything off except the dynon, AP, and gps. I mean even turn off the field for the alt. OF course if it works fine, just start turning things back on.

The Trio was only a roll autopilot. The Dynon works perfectly in roll, but not in pitch. This leads me to believe the problems are related. Unless of course we're talking about voltage fluctuations or something. That's the only scenario I can come up with, but the Dynon pitch servo is behaving smoothly, just incorrectly which would probably lead me away from the electrical problem theory.

During the course of testing the Trio I did turn everything off except the ALT field. I have a Plane Power alternator and they say it's fine to turn the ALT field on and off in flight, so maybe I'll give that a try.

Bryan Wood
11-25-2008, 10:30 AM
Jamie,

Here is something else you can try. If you can get to the static lines under the panel vent everything connected to it except the altitude hold to the cabin for a test flight. Then connect only the altitude hold to the static system which will simulate adding a stand alone static port for the altitude hold which is known to cure this type of problem. Then go fly and try various gain settings and see if this helps. I'll bet you a coke that this makes your problem better.

Jamie
11-25-2008, 11:12 AM
Jamie,

Here is something else you can try. If you can get to the static lines under the panel vent everything connected to it except the altitude hold to the cabin for a test flight. Then connect only the altitude hold to the static system which will simulate adding a stand alone static port for the altitude hold which is known to cure this type of problem. Then go fly and try various gain settings and see if this helps. I'll bet you a coke that this makes your problem better.

Bryan:

I have vented the Dynon EFIS (which drives the AP) to the cabin and it behaved the same. That's why I pretty much excluded the static system as an issue.

You seem to be suggesting connecting just the EFIS to the static system and nothing else, right? If this works, wouldn't it imply that there is a leak in one of the other static-connected instruments?

Bryan Wood
11-25-2008, 11:38 AM
Bryan:

I have vented the Dynon EFIS (which drives the AP) to the cabin and it behaved the same. That's why I pretty much excluded the static system as an issue.

You seem to be suggesting connecting just the EFIS to the static system and nothing else, right? If this works, wouldn't it imply that there is a leak in one of the other static-connected instruments?

No, your thinking to much. I'm suggesting you go to the extreme correction to prove or disprove the static system and all associated components (which were still hooked together with the autopilot when you vented to the cablin, weren't they?) as your cause. If this helps then you can start thinking about why, such as diaphrams in your instruments inducing surges, or leaks, or whatever. If it doesn't work you can look to your electrical system or the autopilot itself. My money is on the static system or related components. Another method that you might try is to put an accumulator in the static line for testing only. Basically a sealed cannister with enough volume that it will dampen out surges or sudden changes giving you a nice smooth pressure at the autopilot transducer. If this works it will likely make the autopilot slow to respond to altitude changes so it wouldn't be a good idea to leave it in there long term, but might help to prove or disprove your static system as your problem.

Another thing you might try is to get the plane just slightly out of trim so that without using the altitude hold you feel very slight pressure on the stick to hold altitude. When you get this to where it is almost not noticable, but you will certainly climb or decend when you let go of the stick try the altitude hold again and see what it does. (This assumes you don't have auto trim available with your autopilot. If you do and can disable it do.) Often the servo likes a slightly out of trim condition better to keep from osciallation on both sides of null. If this helps your problem is with the autopilot.

Jamie
11-28-2008, 02:56 PM
I am making progress resolving this issue.

Yesterday morning I went out and flew some flight tests aimed at determining the stability of the airplane. If the airplane is unstable, then obviously the autopilot may have trouble.

I performed a couple of phugoid tests. As expected the airplane dampened out nicely with just a couple of oscillations. My airplane is definately pitch stable. I also trimmed the airplane to see how long it would hold altitude/heading with no intervention. I gave up after 10 minutes. :-)

Today I had an opportunity to make a 100nm trip (200nm round trip) and had lots of time to play with the autopilot. I decided to try putting slight load on the servo by trimming the nose down. The Dynon AP will indicate on the EFIS if the servo needs up or down trim. I trimmed nose down just until the nose up trim indicator would hold steady. Doing this, I was able to get the autopilot to hold altitude very well. With the airplane slightly out of pitch trim the airplane handled as it was supposed to -- too high of a sensitivity and you could feel the airplane overworking to stay at altitude. I backed the sensitivity down a little and it smoothed out.

I know of at least one other autopilot manufacturer with auto trim that will actually trim the airplane out of trim (they call it bias) to deal with slop in the control system. Every control system will have a little play in them because of the bearings.

I know that other autopilot manufacturers also introduce a 'deadband' setting. I understand this setting exists to deal with minor slop in the control system. The Dynon AP does not appear to have this type of setting.

My next course of action is to go back into the back and double check the control system for any unnecessary slop (seems like from the bellcrank to the elevators is all that's important). Again, I could have a bearing that has a little too much play in it, etc. but my RV appears to have the same amount of slop (very minimal) as other RVs.

pierre smith
11-29-2008, 07:06 AM
....and I've been following this thread since I'm about to install my TT servos. The bias helping stability is interesting. I also have a very slight 'play' in my elevator system from the stick to the elevators but not from the rear bellcrank to the elevators so that 'should' be ok.

Regards,

rvmills
11-29-2008, 12:46 PM
Jamie,

Like Pierre, I'm following along as well. My Dynon servos and AP-74 are in, but I'm having issues with the 5.0 update (working with Dynon on it) so I'm playing catch up ;)...thanks for leading the way!.

I was just wondering what torque and sensitivity settings you are finding work best...pretty close to default, or did you have to make large changes? (I know every plane may be different, just wonderin'!)

Interesting note on the pitch trim findings...good to keep in the bag o' tricks!

Thanks, and sounds like you're dialing it in nicely!

Cheers,
Bob

jthocker
11-29-2008, 08:25 PM
Bob
I'm having issues with the 5.0 firmware also. What's the problem you're having? My problem is, that after updating the D180 to 5.0 as per directions, then trying to update the AP74 and servo's I can no longer connect to the D180. My laptop has always had some issues with the Dynon Support program unless it was acually connected to the D180. This time I tried 2 different laptops and 2 dif. USB cables. I get a " chip communication" type error. The D180 was overnighted to Dynon on Wed.
Incidently everything appears ready to go except 1 servo says "upgrade needed".
Regards
Jon

rvmills
11-29-2008, 09:41 PM
Jon,

My issue is probably self-induced. I had trouble getting the driver installed for the USB to Serial cable, then when that was fixed, I had trouble getting the product support program to recognize the D-100. I had both my D-100 and D-10A, as well as the AP-74 and servos powered up (based on my interpretation of the query "are all DSAB components powered up and connected").

So I tried turning off the avionics master to shut down the D-10A, and hit the "ack" button on the D-100 to keep it on. I intended to turn the av master back on to have the D-100 running on ship's power during the update (instead of the D-100 backup batt). At that point, the support program recognized the D-100, and I got excited and jumped the gun and started the update on the backup battery (by mistake). When I realized what I had done, I was afraid to switch power sources, and let the 5.0 update run on the D-100 backup batt. The backup batt held throughout, and all went well till the very end, when the program rebooted the D-100, and I received the error msg on the yellow screen. Couldn't get the program to recognize the D-100 after that. So I'm calling Dynon on Monday, and may have to send my D-100 in as well. I'll ask them for a clarification on the servo update when I call as well, and let you know what they tell me!

So close...:rolleyes:

Cheers,
Bob

dynonsupport
11-30-2008, 11:38 AM
Everyone,
We've had some issues with people updating EFIS units to 5.0 while running only on the internal battery. While this seemed to work OK in the past, it's causing issues now. We're investigating why.

For now:

PLEASE MAKE SURE YOUR EFIS IS RUNNING ON MASTER POWER WHEN UPDATING

rvmills
11-30-2008, 12:05 PM
Everyone,
We've had some issues with people updating EFIS units to 5.0 while running only on the internal battery. While this seemed to work OK in the past, it's causing issues now. We're investigating why.

For now:

PLEASE MAKE SURE YOUR EFIS IS RUNNING ON MASTER POWER WHEN UPDATING

DS,

Thanks for the reply! Can you speak to the issue (discussed here and in another thread) of updating the AP servos to 5.0. Seems that some are having trouble, in that when they do the EFIS/AP Servo update, it tells them that the EFIS is updated, but then the update program does not sequence to the AP Servos. Is there a step, or trick, to have the update program move to the servos? (That is under the assumption that the servo status says "Update Req").

Thanks much!

Cheers,
Bob

dynonsupport
11-30-2008, 05:08 PM
I believe that issue is related, but I can't say 100%. I'll try and get a more informative update tomorrow when I can ask the software team.

Jamie
12-06-2008, 05:40 PM
Today I spent a couple of hours doing misc. maintenance on the airplane, then pulled the baggage wall in order to check for slop in the control system. I taped the elevators into trail and climbed into the fuselage. I am unable to move the servo pushrod or servo arm. In other words, there is absolutely no slop whatsoever between the servo and the elevators.

I am completely at a loss here, but I'm not giving up. At least I have a 'solution', which is to fly the airplane out of trim. However, I am super anal about things working the way they're supposed to so this is driving me freakin' nuts.

Anyone else have any ideas?

dedgemon
12-06-2008, 07:23 PM
I don't think the issue is slop in the elevator pushrod/servo path. Its the slop in the trim linkage that is the problem. I think that what you are seeing is a non-linearity induced stable limit cycle due to a little (or a lot) of deadband in your trim system. This slop in the trim allows the tab to flip one way or the other, this in turns puts a force on the elevator, which moves the plane in pitch, the autopilot responds and the oscillation begins when the tab flips the other way.

By trimming the elevator one way or the other you've taken the deadband out of the trim tab linkage and this has the effect of removing the non-linearity that is perturbing the auto-pilot. This allows everything to settle out since the trim tab isn't moving across the deadband.

All of the RV's have some compliance in the trim system, but whether yours is too much or not also depends on your planes exact CG, decalage of the stab etc...

Its just about got to be a mechanical linkage issue with the trim tab.
...
I hope. :rolleyes:

good luck

Jamie
12-07-2008, 01:15 PM
Thanks, David.

That's a good thing to check. I did a cursory check of the trim a while back and couldn't find any play in it, but I'll do a very thorough check of it again just to be sure.

A friend of mine that used to run an avionics shop told me that they would often have problems with altitude hold units in certain airplanes that were subject to oil canning on the elevators. I have absolutely no oil canning on my elevators but I do have some on the bottom of the fuselage (as documented in this thread (http://www.vansairforce.com/community/showthread.php?t=36763&highlight=oil+canning)).

At this point I'm curious if this oil-canning could be contributing to the problem.

dedgemon
12-07-2008, 04:44 PM
its a little hard to know what the trim "should" be like. Mine on the '9A has a fair amount (1/2" at the trailing edge) of combined "slop" (manual trim). It flies fine (admittedly with no autopilot). My 8 has almost no slop (also manual trim, go figure). How your airplane will behave is a function of its rigging, exact CG, etc... but I would tend to guess that less slop is better.:eek::D
Good Luck

Jamie
12-08-2008, 05:41 AM
I went out last night to check the trim tab and there's absolutely no play in it whatsoever. I guess I can check that off the list.

BTW: I have electric trim.

Jamie
12-10-2008, 01:15 PM
If anyone else has the Dynon AP installed, can please move your stick in the following positions and tell me the position number as displayed in the EFIS's AP status screen? Thanks!

full pitch up:
neutral:
full pitch down:

I'm trying to figure out exactly what is unique about my installation. Supposedly I'm the ONLY person having this issue so far and I just can't see how that's the case.

In fact, if you have a Dynon AP and the pitch is working fine, could you please just chime in and let us know!

As far as I know I'm one of the very few that isn't a better tester.

Here are my numbers:

full pitch down: 57
full pitch up: -147
pitch neutral: -18

Since we know that there are 800 steps in the motor, it means that my AP arm is swinging ~92 degrees stop to stop.

Alschief
12-10-2008, 07:51 PM
We just installed ours and have a couple of test flights completed.
D100 only, no AP74 installed.
The both pitch and roll seem to be working well.
I will try to get the data you requested in the next couple of days.

rvmills
12-11-2008, 12:41 AM
Jaime,

Just received my D100 back from Dynon after a 5.0 glitch (self-caused, I believe). Did the DSAB config, and servo and AP-74 updates today, and will calibrate and (hopefully) test-fly tomorrow. Will report back on pitch effectiveness, and look for those numbers.

It may become obvious when I run the cal, but just in case, where is the menu page that you're referring to (is it on the DSAB page, scolled to servo status, or in another menu?)

Thanks, and backatcha as soon as I can git 'er done!

Cheers,
Bob

Jamie
12-11-2008, 04:56 AM
It may become obvious when I run the cal, but just in case, where is the menu page that you're referring to (is it on the DSAB page, scolled to servo status, or in another menu?)

Thanks, Bob. The menu is: SETUP->AP->STATUS. I'm working from memory here, so it may say something like "SERVO STATUS" instead of STATUS, but it should be obvious at that point. :)

Thanks, Guys.

Jamie
12-11-2008, 05:29 AM
We just installed ours and have a couple of test flights completed.
D100 only, no AP74 installed.
The both pitch and roll seem to be working well.
I will try to get the data you requested in the next couple of days.

Have you tried it up at cruise yet (i.e. 155kts, 8500ft) on a long trip? Mine will seem like it's holding fine for a minute or so and then the oscillations will begin.

Are you computer savvy (this goes for anyone reading). If you could turn on the datalogging and download and e-mail me your datalog that would be a HUGE help. I would like to compare the dynamic performance of other installations to mine.

Unfortunately Dynon does not log the servo positions in the log file. It is hard to fathom why they do not do this. The only thing I can think of is they do not want to publish how they are flying the airplane. If they publish the servo positions in the log file one would know almost exactly what the AP is doing to fly the airplane level (at least within the 1 second resolution of the log file).

dynonsupport
12-11-2008, 11:44 AM
The datalog was built to record the sorts of data that would be useful to customers in their own analysis. When you get really into it, there are lots of deeply technical things that COULD be logged that we choose not to (the resistance of some random circuit, for example). There also a size constraint too - if you add too many things to the log, you end up not having a whole lot of recording time at 1Hz. Anyway, in troubleshooting your case, having that data isn't valueless, but also probably wouldn't be a panacea. We'll be looking into whether we should add that data to the log.

Also, while we're happy to see this thread out there, please make sure to send technical data or things you're trying directly to us via the email thread with the case number in it. This lets us track our progress in getting your issue resolved directly.

Alschief
12-11-2008, 12:07 PM
I checked my Pitch Servo numbers today on the ground.
Centered -00001
Forward +00070
BAck -00107.

I can try data logging Friday, weather premitting.
I have traveled about 50 miles @ 3500' with steady altitude
no hunting.

Jamie
12-11-2008, 12:45 PM
Also, while we're happy to see this thread out there, please make sure to send technical data or things you're trying directly to us via the email thread with the case number in it. This lets us track our progress in getting your issue resolved directly.

I have been doing this and of course will continue doing so. I'm just gathering data at this point. Obviously there is something funky going on...just trying to gather as many data points as possible. :cool:

jthocker
12-11-2008, 04:17 PM
Jamie
My servo's are Pitch up -108
neutral +004
down +081

Roll left +101
neutral +011
right -098

My initial reaction to my autopilot performance is disappointing.
With that being said, I have had only 3- 15 minute flights with it and have not been able to go thru the inflight adjustment program.
With the default settings 100% torque, sensitivity 10.
Altitude hold +/- 60 ft., VSI rates to recapture 100-400 fpm.
Heading hold +/- 10 deg.
Nav hold +/- 10 deg. constant heading changes.
Reset sensitivity to 5 on both axis's not much change, and then
I had to land at the paint shop.
So, now I'll have a couple of weeks to explore the Dynon manual and see if there's going to be something to adjust. I sure hope there is!!!!

Dynon has been a great company to deal with. I have faith that their autopilot will eventually perform as well as the Tru Tracks I've become accustomed to.:D

Alschief
12-11-2008, 04:48 PM
Just did a 30 min test flight.
My altitude is rock steady 2350' +/- 5'
We turned on the Data Logger but it will be Friday before I can send.
The roll does seem to hunt some.


We watched the servo data while in AP mode.

Pitch data was DISC:N POS: -47
REV:N FRC: -00023 to -00028 varies

Roll Data was DISC:N POS: -00001 to -00003 varies
Rev:N FRC: +13 to +2 varies

jthocker
12-11-2008, 07:26 PM
After spending some time at home reading the Dynon D180/AP installation manual, regarding flight tuning. It appears that my brief flight and attempt to tune the servo's was exactly the opposite of what I needed to do. Upon initial engagement of the autopilot, there was some abrupt movements of the stick. I took that to be a "twitchy" movement and decreased the sensitivity.
I should have increased the sensitivity. :o
The weather here in Cincinnati has been crappy, my 15 min. flight to the paint shop was at 500 AGL, scud running with good vis., but towers between HAO and 3I7(Phillipsburg). So my attention was not on tuning the AP.
The plane is now disassembled at the paint shop, so I am hopeful that I'll get it "dialed in" in a couple of weeks.

Jamie
12-11-2008, 07:44 PM
I may have found my problem tonight.

I engaged the pitch servo and then tried to move the stick fore and aft WITHOUT making the servo slip. The elevators were visibly moving several degrees. Going to the SETUP->AP->STATUS page I could see that the motor was staying on the same step.

Next I put the servo in TEST mode....the reason I did this is because the servo will not hunt in this mode -- it just stays on one step. Then I went back to the elevators and used my Craftsman digital level (similar to a Smart Tool). I was able to measure ~4 degrees of travel without the servo slipping. This is not good. I was able to 'wiggle' the elevators with very little force about ~3 degrees. Again, not good.

So I pulled the baggage wall and crawled (yet again) into the baggage area. Pushing and pulling on the pushrod I noticed that the servo arm was rotating slightly on the shaft.

I pulled the access cover on the right wing to inspect the behavior of the roll servo. It looks like it's doing the same thing.

I already spoke with my contact at Dynon and he's sending me two new servos. I will try them out to see how it works.

For comparison's sake I went over to my buddy's hangar where he's getting ready for his first flight (hopefully it'll fly this weekend). He has a fancy Trutrak with vertical speed select, etc. I tried the same exact test. His elevators are LOCKED into place when the servo is engaged.

In my opinion, the problem has been found. I'm not quite sure where to go from here. I will install the new Dynon servos, but I'm very curious why both of my servos have arms rotating on the shafts. They have consecutive serial numbers, so maybe it's just a fluke and the new ones will not do it, but only time and a couple more hours swapping out the servos will tell. I'm not ready to declare a design flaw....yet.

So can someone please do this test for me?
Go to SETUP->AP->SERVO TEST.

Get the AP test to move the stick to a particular location (doesn't matter where) and then put a Smart Tool or similar tool on the elevator to see how much you can move it without having the servo slip.

I'm curious to see if other folks have the same slop in the servos.

Oh yeah, I did the same test on my ailerons...checking the amount of movement I can get out of them with the servo on one step. I was able to move my ailerons 5.5 degrees without the servo slipping......and I know there's no slop in that control system -- the servo is at the bellcrank...very easy to check for slop there since there's only two pushrods involved (aileron->bellcrank and bellcrank->servo).

rvmills
12-11-2008, 08:26 PM
Jaime,

Did my first test flight today. Started out at the default torque and sensitivity settings (100%/10) on both servos.

For Roll, heading seemed to wander quite a bit, so I upped the sensitivity to 15, then backed it down to 13. Still wandered some, though a bit less. It was a bit twitchy as well (little bumps in the stick), so I need to play with it more. Then my Dynon compass started swinging, so I stopped the roll test, and need to re-cal the compass (Dynon instructions say that may be necessary, and though heading looked solid on the ground, it must need the re-cal...it may be the true cause of the heading chase).

And Jon, in reading, I think you were doing the right adjustments...wandering calls for increasing sensitivity, and overly twitchy (agressive) calls for decreased sensitivity.

For Pitch, the initial test went pretty well. Held altitude pretty smoothly for several minutes. When I engaged, I was about 70 feet higher than I intended and holding (8,570), so after a while I reset the ALT selector to 8,500, and trimmed slightly down to capture as shown on the DN annunciator. As it captured, it started to give me UP, then DN indicators, as it started some mild up and down pitch occillations. I have manual trim, and was making really small corrections, but it couldn't seem to dampen itself, so I disconnected and re-set it up. Held ALT pretty smoothly when I set it up carefully (trimmed, etc.)

It was a short test, and I'll redo, and expand the test next time. Will also turn on datalogging, and will record the position and force numbers in flight, like Al did.

My position numbers on the ground are:

Pitch: +73 to -117
Roll: +77 to -133

Forgot to check neutral...will also get that next time.

I just saw your last post Jaime...very interesting. Just to clarify, is what you're saying that you can see the servo arm(s) rotate on it's shaft back and forth a bit before the servo slips? And that translates into the wiggle or play you found in the control surfaces, right?

Will try the test you asked about, but wondering something. The test puts it near full deflection in two axes, so I'll check for play there, but seems like a good follow-on (especially if there is no play at full deflection) would be to engage ALT and HDG hold with stick neutral, and check for play there, as that is where (or near where) the surfaces will be in flight. That way we can look for dead bands or play near neutral, both in the servo arm and the control surfaces.

Will report back with what I find, and good luck with the new servos!

Hey, if it makes ya feel any better, I had to open the baggage bulkhead (again), and fiddle with the wiring connectors...seems my pitch servo went undetected, and I had to test all the connections in the "spaghetti" of my quick disconnect. All was good, and when I put the QD back together, lo and behold, there it was (I got lucky on that one...did not want to re-wire!!)

Good luck...we'll get there!

Cheers,
Bob

dynonsupport
12-12-2008, 11:37 AM
Bob,

Couple of quick setup tips:

- Try 15 to 18 on pitch sensitivity.

- HDG mode requires a good compass cal, but you can set up the AP in TRK mode if your compass isn't in cal.

- The trim up/trim down annunciations arent necessary for the autopilot to hold altitude so long as the servo isn't slipping. If you follow them however, the airplane will be in trim when you turn the AP off.

Jamie
12-12-2008, 11:57 AM
Hi Bob...excellent info...thanks!

Yes, the AP TEST mode puts it in the extreme positions, but the reason to do it that way is because if you just engage the autopilot on the ground it will continuously 'hunt' and will be changing steps occasionally so it isn't really a good test. If you use the test mode it doesn't hunt. What I did was just engage the test then using the stick put the control surfaces trail.

Yes, the servo is sliding slightly on the shaft. Of course a tiny movement at the shaft equates to a much larger movement at the end of the arm where the pushrod connects. The pushrod then connects to the elevator bellcrank which then magnifies the slop.

Also, as mentioned in a previous post I taped the elevators into trail and tried to move the servo pushrod by hand and it wouldn't budge...so that leads me to believe that the 4 degrees of travel I'm seeing at the elevators is the result of the arm slipping on the servo itself. I can also visually observe the slipping, so it seems to me like a reasonable conclusion to come to.

It's as if the sheer pin does not provide close enough tolerance and is 'wallowing' in the hole through the shaft.

jthocker
12-12-2008, 02:16 PM
Jamie
I just got back from the airport. While my plane is now at the paint shop and I'm unable to do any tests on it, my hangar mates RV8 is available.
This is the twin to my RV8 that was completed in April 08. This plane has a Tru Trak ADI II in it instead of the Dynon.
I engaged the AP and measured the "play" in both the elevators and ailerons.
1 degree at the elevator, and .5 degree at the aileron.
Good Luck
Jon

rvmills
12-12-2008, 06:54 PM
Jaime (and DS):

Did the following today:

Ran the servo test and checked for slop in the control surfaces and at the servo arm. Found the following:

With very light fingertip pressure at the outer corner of the aileron, it moved about 1/16th to 1/8th inch in each direction (eyeballs only, no protractor, so I don't have degrees, but it was small). With the same very light pressure on the corner of the elevator, it did not move. However, if I applied a little more pressure at the center of the aileron or elevator (just enough pressure to keep the servo from slipping...a little more and it ratcheted), each surface moved about 1/4th to 3/8th of an inch in each direction (more than I had hoped for, but the flight test went OK, as I describe below).

Then I looked at the roll servo arm through the viewing window I made for the floor, and with the servo in test, I could move the stick enough to make the servo arm move about 1/4th inch in each direction, and the ailerons moved about the same as the second test above (all without servo slipping). Pitch movement at the stick seemed about the same...just a bit of slop in the stick...but I didn't pull the baggage bulkhead to look at the P servo (couldn't bring myself to pull those screws again! ;)).

I did try it in HDG/ALT Hold on the ground, and the results were about the same (as in both of the first tests). I did note the hunting you described, and it made the test less conclusive, just as you described.

I then did a compass cal, and then flew a test hop (and Dynon was right, the cal did wonders for HDG hold). Things went pretty well on the test. Felt a little more twitchy in roll than in pitch, and I ended up decreasing the sesitivity to 7 for roll and 8 for pitch, and it performed pretty well. A little overshoot and hunting in roll, and an occasional pitch occilation, but overall pretty good. Turns to heading were pretty good, with a little twitchiness in the turn and a few corrections to nail the new heading. Climbs went pretty well too. One thing I noticed is that if I left the pitch trim alone if it was hunting the altitude a bit after level off, and didn't chase the UP/DN annunciators with manual trim, it did better than if I reacted to each trim annunciation and trimmed (unless the annunciation was on for a while). I also noticed that having the ball in the center and being smooth with the rudders made a big difference in HDG hold (go figure! :))

I won't call it locked in, as it still seems a bit jiggly (good technical term), but it's probably just me getting used to the difference in a light duty AP on a nimble little plane, versus the heavy iron with the high dollar AP.

Some background info for comaprison:

- SV-32 servos
- RV-6, with clipped wings and a big gas guzzler up front.
- My seller and F1 Rocket driver said it's lighter on the controls than his F1
- Test at 8,500 to 9,500 MSL (3-4K AGL), with light winds, very occasional light chop.
- Flown at about 1,700# (1900# GW Airplane)
- Speed was about 165 KIAS / 180 KTAS (a bit less in climbs)

Today's position and force readings were:

Ground:

Roll...Left -90, Neut +11, Right +110
Pitch...Fwd +116, Neut +30, Aft -71

In Flight, Straight and Level, HDG and ALT Hold engaged:

Roll...Pos +15 +/- 5 (+10 to +20); Force +18 +/- 5 (+13 to +25)
Pitch...Pos + 25 +/- 5 (+20 to +30); Force -10 +/- 5 (-5 to -15)

Those in-flight numbers are a bit of a SWAG, as they move around a lot, as you know. Looks like the inflight positions were close to neutral in S&L flight, so that's probably a good indication (and the off-neutral numbers were probably a combination of whatever deflection the controls have at that speed, as well as perhaps an indicator of a very slightly out of trim elevator, and maybe an indicator of when I did not have the ball centered or was too touchy on the rudder).

I'll keep working it, especially if I get a chance to fly on a little X-C, and see how I can dial it in. Not sure how my control surface movement results compare with yours, but I'll keep an eye on it as I work to tweak it all.

Best of luck with your new servos, very interested to hear if the servo arm and surface movement remains, or decreases/goes away!

And DS, thanks for the tips. Will try various settings and see how they each work. And my compliments on your manuals, they do a great job throughout. If the last DS poster was Ian, thanks to you and Mike for all the help along the way, and Ian, congrats on the new baby!!

Cheers,
Bob





Bob,

Couple of quick setup tips:

- Try 15 to 18 on pitch sensitivity.

- HDG mode requires a good compass cal, but you can set up the AP in TRK mode if your compass isn't in cal.

- The trim up/trim down annunciations arent necessary for the autopilot to hold altitude so long as the servo isn't slipping. If you follow them however, the airplane will be in trim when you turn the AP off.

Hi Bob...excellent info...thanks!

Yes, the AP TEST mode puts it in the extreme positions, but the reason to do it that way is because if you just engage the autopilot on the ground it will continuously 'hunt' and will be changing steps occasionally so it isn't really a good test. If you use the test mode it doesn't hunt. What I did was just engage the test then using the stick put the control surfaces trail.

Yes, the servo is sliding slightly on the shaft. Of course a tiny movement at the shaft equates to a much larger movement at the end of the arm where the pushrod connects. The pushrod then connects to the elevator bellcrank which then magnifies the slop.

Also, as mentioned in a previous post I taped the elevators into trail and tried to move the servo pushrod by hand and it wouldn't budge...so that leads me to believe that the 4 degrees of travel I'm seeing at the elevators is the result of the arm slipping on the servo itself. I can also visually observe the slipping, so it seems to me like a reasonable conclusion to come to.

It's as if the sheer pin does not provide close enough tolerance and is 'wallowing' in the hole through the shaft.

Jamie
12-12-2008, 08:45 PM
Wow, you guys are fantastic. Thanks so much for going the extra mile to help a fellow RVer.

Bob: The movements you describe are certainly far less than what I'm seeing. It's looking more and more like all of the evidence is pointing toward slop in the system (the servo in this case). Every data point I have so far points to that...including being able to fly out of trim and have the AP hold altitude.

I'm very hopeful (but not tooooo hopeful) that the new servos will solve my problem.

Thanks again, guys.

Jamie
12-13-2008, 12:21 PM
Received the new servos today! Will install them tomorrow and report back.

647jc
12-13-2008, 04:27 PM
Jamie,

I checked my Dynon AP installation on my RV-9A today and the arm of the servo definitely has a sloppy fit on the servo shaft allowing the arm to move around a bit when the shaft of the servo is locked or holding on a step. This slop allows about a +/- 1 inch movement at the trailing edge of my elevator, similar situation for my ailerons.

My plane has only flown twice and I do not know if the AP is working properly or not but there is definitely slop in the arm connection to the servo shaft. I don’t know if this is correct or not, it appears there is some kind of nylon bushing near the arm so there may be some intentional dampening or cushioning designed into the connection of the arm to the shaft but what I see appears to be a bit much. My servo serial numbers are 1095 and 1131, they were shipped 10/9/2008. Perhaps there was an undetected assembly problem at Dynon at that time.

I am anxious to hear if your new servos also appear to have loose fitting arms.

flickroll
12-13-2008, 05:16 PM
I'll double check my servo arms tomorrow, but as I remember there is NO slop in them. I do know the elevator is tight, i.e. no movement/slop.

Jim Shannon
RV-8 N52VV
Charlottesville, VA

Sam Buchanan
12-13-2008, 05:59 PM
I won't call it locked in, as it still seems a bit jiggly (good technical term), but it's probably just me getting used to the difference in a light duty AP on a nimble little plane, versus the heavy iron with the high dollar AP.

Keep dialing it in, you will be amazed at how well a "light duty AP" will fly our little planes! Once the system is debugged it should fly the RV very smoothly with no detectable oscillations or jiggles. Other AP vendors have it figured out and no doubt Dynon will crack the code, too. :)

Getting a new autopilot sorted out can be a circuitous path--you fix one issue and break another. But the digital AP technology works splendidly in our planes and we are fortunate to have several solid systems from which to choose.

rvmills
12-13-2008, 10:00 PM
Keep dialing it in, you will be amazed at how well a "light duty AP" will fly our little planes! Once the system is debugged it should fly the RV very smoothly with no detectable oscillations or jiggles. Other AP vendors have it figured out and no doubt Dynon will crack the code, too. :)

Getting a new autopilot sorted out can be a circuitous path--you fix one issue and break another. But the digital AP technology works splendidly in our planes and we are fortunate to have several solid systems from which to choose.

Thanks Sam, appreciate the words of encouragement! The comment wasn't meant as a slam on the AP or the RV at all (just noting the differences so far)...of course, I would much rather be playing in the RV, and I'm actually having a lot of fun doing the install and testing, after doing a panel upgrade. It's been enjoyable to see it all come together and start working, and when I get it tweaked in, it'll be really satisfying to hit the button(s), watch it do it's thing, and sit back and say, "I did that"! (with the added benefit of X-C flights with my boys and being able to relax and point out neat stuff along the way and watch their eyes light up). Pretty cool (not as much fun as wringing the RV out with the autopilot off...which is most of the time in the air...but another kind of fun, just the same!)

I think you're right about the circuitous path...the roll and pitch modes probably interact a bit, and dialing it in will be a fun project. Very pleased with the process and performance thus far! And learning and troubleshooting a new product as a community of flyers is pretty fun too! Good stuff!

Cheers,
Bob

Jamie
12-15-2008, 05:36 AM
I installed the new servos yesterday. I have to say that swapping them out wasn't too bad. Trutrak really did a good job when they designed those mounting brackets. ;)

The worse parts were removing the baggage wall and safety wiring the AN3 bolts on the new servos.

Here are my initial findings. The elevator travel is now reduced to about 1 degree or so. That's definately an improvement. I will occasionally perform this check to see if the throw increases over time. If it does...well there's something wearing in the servo.

I went out and flew the new servos yesterday. All of the area metars except my home field were reporting scattered 1400ft, overcast 5500, but I went out to have a peak and everything was completely overcast at 1400ft and it was quite turbulent down below.

In other words, I wasn't able to get in a proper test flight. The altitude hold seemed to be working OK, but it's impossible to measure any improvement in performance unless I can fly in smooth air. Forcast this week is looking grim -- seems that Thursday will probably be the earliest day I can test properly.

647jc
12-15-2008, 09:04 AM
Jamie,

It sounds like the new servos also have a bit of slop in the connection of the arm to the servo shaft. Could you please estimate the free travel of the elevator trailing edge now when the new servo is locked on a step, you mentioned 1 degree or so, about what would that be in +/- inches?

Perhaps DynonSupport could provide a brief description of the connection between the servo arm and shaft, apparently some slop is acceptable and possibly designed into it since multiple installations have reported it. Perhaps this is to provide a dampening effect? I would sure feel better if I knew the slop in my installation was normal rather than spend a lot of time trying to adjust a system that is out of tolerance.

dynonsupport
12-15-2008, 05:57 PM
There should be no movement between the output shaft and the output arm. (Some play in the output shaft bushing is normal.)

If you believe you have play between the output shaft and the output arm, please contact us via email at:

support@dynonavionics.com

Or call us at
(425) 402-0433.


Re:

Jamie,

It sounds like the new servos also have a bit of slop in the connection of the arm to the servo shaft. Could you please estimate the free travel of the elevator trailing edge now when the new servo is locked on a step, you mentioned 1 degree or so, about what would that be in +/- inches?

Perhaps DynonSupport could provide a brief description of the connection between the servo arm and shaft, apparently some slop is acceptable and possibly designed into it since multiple installations have reported it. Perhaps this is to provide a dampening effect? I would sure feel better if I knew the slop in my installation was normal rather than spend a lot of time trying to adjust a system that is out of tolerance.

Jamie
12-20-2008, 07:17 PM
Here's the latest update in my saga.

I installed the new servos and returned the old servos to Dynon.

Dynon replied to me that they did not find any play in the servos. I find that quite strange, since I know that my eyes weren't deceiving me. You can't see the movement with the servo off...only with it on.

Anyway, I installed the new servos but the servo I installed in the pitch position seems to have not had proper factory calibration. It is reporting servo friction on the ground with no load on it.

The result is that as soon as the AP is engage on the ground it reports that I need down trim. In the air I have to add a significant amount of down trim to get the down trim indications to show level flight.

At first I thought this was done as a one-off build of the firmware just for me since I previously reported that when flying the airplane with nose-down trim the AP worked a lot better. My contact at Dynon is telling me that my servos have the latest official build.

I measured elevator throw again. It's still about 1 degree of throw with the servo locked into place (previously it was 4+ degres), and every bit of movement I can see in the system (which is definitely smaller) is at the servo.

I trimmed the airplane and engaged the autopilot. It still oscillates around target altitude same as before. Out of trim it works perfectly, including during climbs and descents.

Maybe I'm just too anal and am expecting too much from this autopilot?

You other guys that have it working properly, do you have the VSI enabled on the EFIS and does it indicate level flight with the ALT hold engaged? Mine is back and forth, back and forth, and you can definitely feel it in your rear. Altitude is varying +/- 20 feet at about .25hz I would imagine.

Alschief
12-20-2008, 10:13 PM
Ours works great. +/- 5 to 10'. No hunting at all

rvmills
12-20-2008, 10:19 PM
Jaime,

Some interesting results, to be sure! Did you see the post by another gent in the "Dynon AP Photo" thread, in which he found the shear screw backing out? I looked on the Dynon forum and did not see any discussion on it, so I asked him a couple questions, and it's possible this is all related. I definitely do not want to jump to any conclusions on that, so I'll ask you similar questions here:

In the servo arm movement you are seeing, is the black arm moving around the silver mounting bolt, or is the entire servo arm, mounting bolt and castellated nut "system" moving together? If it's the former, maybe the shear screw is an issue...but like I said, I don't want to jump to conclusions, and I'm hesitent to start taking the servo arms apart.

How much linear travel are you seeing in the servo arm when locked (in test)? If I recall, I could move the stick a little left and right, and a little fore and aft, and saw about 1/4 inch travel of the servo arm in each direction, while in test, before the servo slipped. Not sure how that compares to yours, or to other APs, or if that is pretty typical (first AP install for me).

On the ground, is it just the trim annuciator you are seeing, or is there another indication of the friction you describe? I've not seen that on the ground at all (for feedback).

For feedback on current performance, I flew on AP a bit last week, and most of the time it was pretty smooth. Got about 15 minutes S&L with ALT and NAV engaged, and didn't have to touch the manual trim. I did see some slight VSI changes, and little altitude changes (perhaps similar to your +/- 20 feet) but ususally did not feel it, and I couldn't begin to put a frequency on it...it really wasn't bothersome. Once dialed in, I don't really know what to expect in altitude hold, but even at work I see some minor deviations (perhaps low freq fughoids) that are pretty much imperceptable unless I'm staring at the VSI and ALT readouts (FWIW). So far it seems pretty capable. ALT hold seems pretty good, HDG hold and NAV seem pretty good too, though I think it still chases those a tiny bit more, and hopefully some more Pitch and Roll "sensitivity training" with the servos will dial it in.

However, there have been a few occasions when I did get some pitch occilations that did show +/- 500 fpm or more on the VSI and were clearly felt, but I thought that they were the result of me not having the airplane stable when engaging. They would not dampen, so I would disconnect and stabilize and re-engage. The fact that it's good when you are out of trim and not so good when you are in trim seems odd. On the occasions when it is flying really well, what happens when you disengage (ie, how out of trim are you?)

I'm still just feeling it out and getting it tweaked in small bites, and feel I need to work it and test it quite a bit more. I won't get back up till next week, but I'll try to measure things a little more closely for you.

Would be interesting to hear from those that have been flying it for a while, hear what they see and feel with respect to these issues, and how tight the Pitch and Roll servos hold assigned parameters! (edit: Just saw Al's post...looks like the bar has been set! :))

Cheers,
Bob

Scott Hersha
12-30-2008, 05:13 PM
Wow, it took me about an hour to get through all these posts and I really feel for Jamie. I think if we all have patience and work together with info, then we will eventually end up with an autopilot that is satisfactory if it is possible. Dynon wants to get this right, but so far it hasn't happened. This is a new system and they are learning too. I also have the AP74, 2 servos, and FlightDek180 and so far autopilot performance is unsatisfactory. My altitude varies by up to 100 feet at vertical speed correction rates approaching 1000 fpm. Heading hold simply doesn't work within reason. Nav trak is a lot better, in that the deviations are more gradual. Heading wanders back and forth continuously in heading, but is a little better in trk or nav. One thing I tried today that helped dampen the altitude deviations was to set a max veritcal speed at 300 fpm. I had 1500 fpm set initially because I wanted to use it for climb, but setting 300 - 500 works better to control altitude deviations. Jamie said he starts out OK in altitude hold but after a minute or so it begins to deviate and the excursions just get worse (at least I think that's what you said). Well, I've found exactly the same thing. Take a look at your vertical speed setting and see if changing it makes it better. As far as heading hold goes, I don't know what to think because when I engage heading it usually starts to wander imediately, even though the heading bug doesn't move. Right now I have both servos torque setting at 100 as recommended by Dynon. My roll servo sensitivity is set at 9. 10 or higher and it gets real 'twitchy', rocking the wings back and forth rapidly. My pitch servo is set at 12. I had it at 20 when I started today as recommended by Dynon, but with 12 the deviations aren't quite as abrupt - still deviates though. I think the TruTrak autopilot - which was rock solid right out of the box without any adjustments in my RV-6 - is a totally different kind of autopilot, so comparisons probably aren't valid. This AP74 is really cool and having an autopilot integrated in an EFIS is too. Plus that female voice that barks out 'autopilot - off' is neat, although I don't really need it right now because when the autopilot is disengaged, everything gets smooth again... (ha ha - a little levity there Dynon). I just hope we can get it figured out. It must be a software detail that needs to be fine-tuned. The beta testers apparently didn't have these problems, so something is up. Dynon wants their new autopilot to work and I believe they are concerned. Mike Huff called me as I was typing this to see if I was doing any better with my upgrade. I had a real ordeal trying to get the EFIS and servos upgraded to 5.0 as many of you did. I told Mike about my trouble with autopilot performance and he wrote down the info I gave him so they could try to help. I think the biggest problem with the upgrade is using a PC that is pretending to be a computer. For us MAC users, using a PC is like trying to start a fire by rubbing two sticks together. It's amazing anything ever works with them. If they could make their software work with an Apple, they wouldn't have these upgrade problems.

Scott
RV-8 Fastback (and I mean fast)

flickroll
12-30-2008, 05:28 PM
Sure hope they get it fixed as I'm installing a system in my -8. It's funny the beta testers were happy - would one of you please chime in with your experience? It would also be nice if Dynon would chime in with their take on the issues and potential solutions.

I agree....once you go Mac you never go back....been a happy Mac user for 4 years now....just wish my company issued Macs :(

Jim Shannon
RV-8 N52VV
Charlottesville, VA

flickroll
12-30-2008, 05:45 PM
Is it possible the Dynon altimeter is not sensitive enough which makes the airplane oscillate when operating with the autopilot? Here's the reason for that question: I have a D100. It is not installed in the aircraft yet, but if I turn it on, let it stabilize, and then carry it from the basement to second floor of my house, the altimeter does not move as I climb the stairs (~20' change). It will eventually show an altitude change, but that takes a while. Maybe what I'm seeing is only because it's not installed in a moving aircraft, maybe not.

Jim Shannon
RV-8 N52VV
Charlottesville, VA

Sam Buchanan
12-30-2008, 06:06 PM
Is it possible the Dynon altimeter is not sensitive enough which makes the airplane oscillate when operating with the autopilot? Here's the reason for that question: I have a D100. It is not installed in the aircraft yet, but if I turn it on, let it stabilize, and then carry it from the basement to second floor of my house, the altimeter does not move as I climb the stairs (~20' change). It will eventually show an altitude change, but that takes a while. Maybe what I'm seeing is only because it's not installed in a moving aircraft, maybe not.

Jim Shannon
RV-8 N52VV
Charlottesville, VA

The Dynon EFIS must have pitot/static info to function properly. You will like it in your plane. :)

az_gila
12-30-2008, 06:37 PM
The Dynon EFIS must have pitot/static info to function properly. You will like it in your plane. :)

...that the Dynon will not work at zero airspeed?

When you have it as a hand held, the open port in the back should work exactly like a static port up and down the stairs....:)

I'd try it with my D-180 but I haven't bought the battery option yet...:)

SteinAir
12-30-2008, 07:00 PM
I don't have much to input other than to say if Mike Huff is on it, it has a darned good chance of getting fixed. Dynon managed to snag him when Chelton closed down their Idaho facility, and what a catch he is. For those of you who don't know, Mike is one of the good guys - really good guys and Dynon was darned smart to get him. He's one smart feller.....

Regarding airspeed and the Dynon...I don't know about their AP, but the EFIS itself won't without it - been there done that.

My 2 cents as usual.

Cheers,
Stein

Brantel
12-30-2008, 07:09 PM
Be patient and keep feeding Dynon the info, they are smart people, they will figure it out. Some report no problems and some report problems. If the no problem reporters are telling the truth, the issue will eventually turn up!

Bet that the next major release of firmware will have more parameters for tweaking! I do process control loops for a living and there is a reason why the I and D belongs in PID. Seems Dynon originally thought that P was good enough or that a fixed value of I and D set at the factory would work across the board.

Elsewere I saw where the HDG hold funtion was not working well for someone and after they did a very good compass calibration, the problems with that went away. Might be something to try.

If Dynon is using a 12 bit A-D converter, they should have a resolution of 7.6171875ft on the altimeter.

rvmills
12-31-2008, 01:33 AM
Scott,

Sorry the issues continue...keep at it! I'm the guy Brian referred to on the compass cal issue. I recalibrated mine after the first flight (in which my heading hold chased badly) and it has been much better since doing that. I think the manual suggests the re-cal after factory service as well, and it really did the trick.

On my 6, I currently have the sensistivity set to 7 for roll and 8 for pitch. I also have the max VSI set at 500, the max turn rate set to 2 deg/sec, and the max angle of bank set to 20 deg.

Turn performance is pretty good...still a little "bumping" of the ailerons in turns, but minimal overshoot. Heading and altitude hold seem pretty good (+/- a few degrees and little wandering in HDG, +/- 20 feet in ALT, only occasional occilations), but I want to play with it more to find the smoothest settings that deliver consistent performance. Altitude changes (the couple I've tried) have been poor -800 fpm to 0 fpm, nose moving up and down with noticible "g" in the butt as it searches for 500 fpm. NAV tracking was good on the couple times I tried it. Still only 4 test hops under the belt, so more work to do.

I'm planning a 2 hour X-C to LA tomorrow, and will play with all the modes, giving each a good chance to be steady or occilate around the desired targets. Will play with all the settings, and see if I can come up with a good combo...then report back here.

I think it'll dial in with practice, and will be worth the effort, based on improvements I've noted in just a few hops.

I will say that Dynon has been very proactive and helpful, and concur with Stein on Mike. Didn't know he was grabbed from Chelton, but he's been a really big help to me!

We'll get there...heck, we're sort of the "Gamma" testers as "near the front end" buyers and flyers!

It would be great to hear more from the beta testers to see what tricks have worked for them. Maybe we could even start a data base of what settings seem to work best for different RV and Rocket models!

Back atcha after the X-C!

Cheers,
Bob

Scott Hersha
12-31-2008, 02:04 PM
Here's the lastest on my autopilot performance problems. Dynon (on their forum) ask me to measure the play in my servo with the autopilot engaged. You do this by going into the test phase which freezes the servos in a position. Then you move the aileron and elevator and measure how much movement you get before the servo slips (a loud bang as the lever arm rachets). On mine, both servos allowed 5 degrees of movement before slippage. That's 5 degrees total of about 2 1/2 each way. I called it in and Lawrence from Dynon called me back with a bunch of other measurements and info to obtain. I'll do that tomorrow or the next day. However, he said 5 degrees is too much for an RV-8 and with that much would have a tough time holding altitude or heading. There's a couple possibilities for this play. An internal problem with the servos; slippage between the lever arm and output shaft (bad), or slop in the aircraft control linkage - unlikely in an RV-8 if built to plans. These are the things I'll be checking in the next couple of days. I'll also be collecting servo movement limits from the setup pages in the EFIS. The worst part of this information gathering is removing the bag bin shelf (not too difficult), and the front cockpit floor (bummer). My servo is mounted under the front seat like a TruTrak, which Lawrence says is just fine. For you other guys experiencing these problems, you might want to check yours too and let us all know what you get. You might want to post on the Dynon forum as well. Look for my post under 'Autopilot Discussion/Torque,sensitivity values to keep all the posts in one easy to find place.

Scott

rvmills
12-31-2008, 10:32 PM
Scott,

Just posted this on the Dynon forum as well...good thread you started there!

I did some more playing with the sensitivity on my AP on a X-C in my RV-6 today. Torque is at 100% (pitch and roll), max VSI is 500 fpm, turn rate is at 2 deg/sec, max AOB is 20 deg.

Started out with the sensitivity I had set after the last test hop (7 roll, 8 pitch). In ALT, I saw more deviations than on my last hop (smooth air on both flights). I saw +/- 60-80 feet, with VSI as much as 650 fpm in each direction. Just for the heck of it, I went to 25, and started working my way down. 25 was way too aggressive, though it held alt more closely (+/- 10-20', but really twitchy). Dropped to 20, then down in steps of 2 (18-16-14). Turns out 18 felt and performed the best today. Little twitching, and altitude +/- 10'...pretty smooth, though it did pitch up and down a little visually...but without any noticible g feel. At 16 and below, the altitude chase began, though less wallowing than at the 8 starting point (+/- 350 fpm, +/- 50-60').

In a commanded descent (rolled ALT window from 11.5 to 8.5, and rolled in a little nose down trim). At sens 18, it chased the VSI just a bit, but settled into 500 fpm +/- 50fpm. It also captured 8500' right on, then chased it +/- 20 feet, then settled down pretty well. 18 seems like the nicest spot on my plane for pitch so far.

In roll, at 7 then 6, heading held +/- 2 degrees, and was pretty smooth. Changing the heading bug for a turn caused a relatively quick roll in to 20 deg AOB, and a bit of pitch chasing...need to work that piece a bit, but overall, it was pretty satisfactory. NAV tracking was overall pretty smooth at those settings as well.

Just some numbers for your quest!

Scott, a question on your control surface tests: How much travel in inches (or fractions) does your 5 degrees (+/- 2.5 degrees) equal. Mine move about 1/8th inch in each direction with light pressure on the corner of an aileron or elevator, and 1/4 to 1/2 inch if I press a bit harder on the center of the surface (with the servos locked in test). Any more pressure and the servo(s) slip. How does this compare to your movement?

I'd be interested to hear what other measurments and readings Dynon is suggesting, so I can duplicate.

Thanks much!

Cheers,
Bob

jthocker
01-15-2009, 03:24 PM
I was having the same issues as Scott was with my servo's. Unfortunately my plane was stuck at the paint shop so I could only watch and assist Scott with his. Since Scott is now taking his plane to the paint shop, he was kind enough to let me have his newly modified(by Dynon) servo's.
We determined that both of our original servo's(4 total) had excessive amounts of "play" between the servo arm and the Shaft/capstan/disc.
This play was translating to about 4.5 to 5 degree's at the elevator(1/2 in. to 3/4 in. at the trailing edge. In my case with an identical RV8 with a tru trak installed that flys rock solid, a comparable test showed less than 1/2 the "play" of the Dynon servo's.
Dynon recognized that this was a problem and has been diligently working on a solution.
The problem lies in the shear screw. A minute amount of "play" in the screw threads in the capstan/disc allows the servo arm to move very slightly, independent of the capstan/disc/shaft. This is BAD!
The fix is to reinstall the shear screw with "Loctite 271 (red)", torque the screw to 1 in./lb, and let set for 24 hrs before proceeding with the re-installation of the servo. Dynon has extensive instructions on how to do all this if you should determine that you might be having a similar problem. Or you can send your servo's back to them and have them do it for you.
Scott volunteered his new servo's so we could carry on as "gamma" testers.
So, as the snow and cold swirled around us yesterday, precluding us from dropping Scott's plane at the paint shop, it was "swap the servo's day" at my hangar. Today, with 10 inches of unplowed snow on the runway at the paint shop airport preventing the delivery yet again of Scott's plane, we launched in my plane for autopilot testing.
After testing with a digital level and seeing elevator/aileron play similar to the trutrak plane sitting beside it, I was hopeful.
In our brief flight we were able to test most modes of the AP74, and I can finally say that this autopilot performs as well as the Tru Trak.
In pitch, it held altitude to +/- 10-20 in light turbulence.
Climbs and descents to a new altitude were at the selected(500 fpm) vertical speed, within 100-200 feet of target altitude the vertical speed rate decreased to about 100 fpm, then a perfect capture of the target altitude.
Heading mode showed +/- 1-2 degree deviations probably due to the yawing in the light turbulence.
Track mode, it kept the pink cdi needle centered.
Nav mode was excellent also. Picking a new "direct to" waypoint 90 degrees off heading resulted in no more than 20 degrees of intercept of the original "direct to" bearing. It then settled in nicely.

I AM EXTREMELY PLEASED WITH THIS AUTOPILOT NOW. Dynon's support has been very good.:D

N941WR
01-15-2009, 03:34 PM
Great news! It sounds like it now performs like my Beta servos.

...Nav mode was excellent also. Picking a new "direct to" waypoint 90 degrees off heading resulted in no more than 20 degrees of intercept of the original "direct to" bearing. It then settled in nicely.

I AM EXTREMELY PLEASED WITH THIS AUTOPILOT NOW. Dynon's support has been very good.:D
Also, Dynon is working on improving its intercept routines. If my head cold goes away, I hope to get out and do some more testing but will probably wait until the cold wave passes now. :(

FrankK90989
01-16-2009, 08:20 AM
.
.
The problem lies in the shear screw. A minute amount of "play" in the screw threads in the capstan/disc allows the servo arm to move very slightly, independent of the capstan/disc/shaft. This is BAD!
The fix is to reinstall the shear screw with "Loctite 271 (red)", torque the screw to 1 in./lb, and let set for 24 hrs before proceeding with the re-installation of the servo.


I did a close study of my pitch servo arm after a few test flights. I found the shear screw loose. but why? Two things #1 the castle nut was loose, not even finger tight. Allowing arm slop, loosening the shear screw. I tightened the nut 1 slot, (firm finger tight).
#2, Loctite 271 used in combo with brass & aluminum has poor locking performance. check their web site , do your own tests. I did reinstall using 271... time will tell.
After tightening every thing up my Dynon AP is performing fine. :cool:
One thing to think about- If the servo arm is sloppy? will the shear screw shear clean and rotate smooth, or will it mush over and drag?

dynonsupport
01-16-2009, 07:28 PM
While the castle nuts should not be loose they must not be torqued above 4.5 in-lb. Overtorquing the arms will increase the force needed to break the shear screw and restrict the freedom of movement of the arm in the event the screw needs to be broken.

This would defeat the safety provided by the shear screw in the event of a servo jam.

Please get in touch with us if you have questions regarding your servo arms.

Thanks,
-Dynon Support

rvator51
01-19-2009, 03:04 PM
The fix is to reinstall the shear screw with "Loctite 271 (red)", torque the screw to 1 in./lb, and let set for 24 hrs before proceeding with the re-installation of the servo.

What tool do you use to measure 1 in./lb?

jthocker
01-19-2009, 07:39 PM
Tom
The cheapest screwdriver that can "torque" that low was one from Grainger, for over 200 dollars.
It doesn't take much of an excuse for me to buy a tool, and if I could think of one other place to use it I probably would have gotten it, but I couldn't. So I sent the servo's back to Dynon and let them do it, for the 10 dollars in shipping.
Best regards

rvator51
01-20-2009, 10:59 AM
I found one at http://www.wihatools.com/200seri/285vario_s.htm for $102. Thats still expensive, but getting closer.

Rocketboy
01-23-2009, 09:42 PM
Jamie,

Enjoyed reading this thread. I think you're close to a fix. My bet is you'll find the worn hinges/rod bearing or structure deformation that is causing this.

At this point, if I was you, I'd start replacing heim bolts and keep pushing/bending on your structure until you find whats wrong. The fact it works well untrimmed screams to me play/slop/deformation in the control chain.

You will get it right.

Bob

Jamie
02-03-2009, 09:51 AM
Anyone else have any updates?

My AP performance seems to have worsened. I'm guessing it's a loose sheer screw.

I've looked for more and more slop in the system. The only slop I see is in the servo itself. The Dynon Support guys think I'm nuts when I say it, but the arm on the servo will move just a little even with the servo locked in on a step. That movement gets magnified at the elevator trailing edges.

I think this is the crux of my problem.

RV10inOz
02-03-2009, 02:29 PM
Automation is usually as perfect as it gets......if set up correct, its most likely that all inaccurate automation stems from mechanical inaccuracy.

I do this for a living and it is what we find time after time!

Cheers!

DB:cool:

rvmills
02-03-2009, 11:41 PM
Anyone else have any updates?

My AP performance seems to have worsened. I'm guessing it's a loose sheer screw.

I've looked for more and more slop in the system. The only slop I see is in the servo itself. The Dynon Support guys think I'm nuts when I say it, but the arm on the servo will move just a little even with the servo locked in on a step. That movement gets magnified at the elevator trailing edges.

I think this is the crux of my problem.

Jaime,

I've been continuing to play with and adjust the settings on my Dynon AP (RV-6 with clipped wings and lengthened fuse...for comparison).

Roll servo seems to still be happy at 6-7 on sensitivity. HDG hold is +/- 1-3 degrees, with little jerkiness or wallowing. NAV tracks pretty solid (seems even smoother than HDG IMO).

Pitch servo is less dialed in. Did a couple X-Cs at 14-15 (sensitivity), and it displayed different "moods" over time. Most of the time it was stable, maybe +/- 20 feet or less, with no noticible feel in the keester during corrections. However, it occasionally starts to oscillate, and then go +/- 50-100 feet, with trim annunciations popping up, and a light, but quite noticible feel to the pitch corrections. Those oscillations seem larger during descents.

Flew a bit yesterday and today, some on AP, and did a level stretch, followed by a descent of 2K on AP during each run. Some minor oscillations when level at 14, and during the descent, it would hover around the preset 500 FPM, but ocasionally oscillate down to -850 FPM, then up to -200 FPM. Changed to 16, then 18, and the oscillations dampened a bit, but were still present (-700 to -300 FPM at the outside). I found that if I used a little pressure on the stick to help stop the oscillation, it would dampen itself, but if left alone, it would continue. Still not as tight as I'd like it to be, and I don't want to be staring at the VSI to babysit the AP.

I too see a little movement in the roll servo arm when its locked in "test". In my test I moved the stick left and right, and saw the movement in the servo arm. Didn't have the baggage bulkhead off when I did this, to watch the pitch servo, but I was able to move the stick fore an aft a bit as well. In each case, "a bit" means maybe 1/2 inch of stick movement (at top of grip), and that translated to about 1/4" or a little more movement at the arm. Not sure if the mechanical advantage at the top of the stick is just moving the servo arm in a null between steps, or if the servo arm is actually moving around the shaft (i.e., possible slop at the shear screw).

I've been wanting to play with the settings before opening up to look more closely at the servos, but have an oil change comin' up, and need to replace a TED antenna, so the floors are comin' up and I'm going to pull the back bulkhead too, to get a good look at the servos. Will report back with what I see.

Here's a Q: IYO, what's the best way to check the arm movement for slop? I'm thinking about disconnecting the control rods from the servo arms, putting the servos in test, and then seeing if the arms wiggle around the shaft, or just move a little between the first ratchets in each direction. I've read that other servos don't budge, but just not sure what would be considered normal or acceptable. What say you (or others)?

Cheers,
Bob

Jamie
02-04-2009, 05:27 AM
Bob:

Your findings with the movement are close to what I measured with my first set of servos (yes, I'm on my second set now). I have not made the measurements on this set of servos since I noticed the worsening performance.

I found that the movement of the arm was related to both rotation of the arm on the shaft and internal gear lashing or slop in the servo itself. The measurement you're observing in the arm is very similar to what I'm seeing.

The way I test it is to engage the AP in test mode, then while engaged I crawl back and get up close and personal with the servo. I then just push and pull on the elevator pushrod and can see the movement of the arm on the servo.

I ran the numbers and I should be able to move my pushrod to the middle hole on the servo arm without getting close to an over center condition, so that's on my list of things to try.

FrankK90989
02-04-2009, 07:53 AM
Folks,
If you inspect your servo arms, check for looseness in all Axis?s relative to the shaft. If the arm is sloppy it will continue to loosen the shear screw.
Both of my servo arms were a tad too loose.

A note fron Dynon for guidance....

"A note on dynon servo castle nuts

While the castle nuts should not be loose they must not be torqued above 4.5 in-lb. Overtorquing the arms will increase the force needed to break the shear screw and restrict the freedom of movement of the arm in the event the screw needs to be broken."

allbee
02-04-2009, 09:00 AM
I think what needs to be done is this:

Tighten the castle nut to the next hole. This will take about 40inch on a torque wrench. What you say? Yup, if this arm is loose it needs to be known if it really is the problem. So I say tighten the nut and run another test, if there is no more slop. Than I say go fly it and see what it does. If it has no more oscilations than we know what needs to be done. Sheer pin won't break until 140inch pounds oh well, use two hands on the stick. At least Dynon will know what's going on and a fix can be gotten.

jthocker
02-04-2009, 10:11 AM
I really hate typing and it appears my post #85 was all for nothing.

allbee
02-04-2009, 10:41 AM
I felt that people tried your fix and it didn't work either. sorry.

RV10inOz
02-22-2009, 10:51 PM
OK folks...... As I had said previously it sounds mechanical!

Well my new servo's arrived and guess what there is movement between the arm and the attachment disc. However the shear screw seemed to be rock solid!

So with the locknut removed and just in my finger tips I played with the fit of the items and to my surprise there was a fair amount (microscopic but large in real terms) of movement of the arm around the head of the shear screw.

I have posted this on the Dynon site and the response I got was .... Do the thread service as per the instructions. Well if you do that the screw is going to be rock solid again but the arm can still move and does move around the shear screw head.

Has anyone else observed this, even after doing the shear screw loctite procedure?

I am not able to fly the plane yet, but some of you guys that are may be able to confirm this. It may not affect every servo, but we are talking about a very small tolerance here and unless you went looking for it you may not find it. If so we should encourage Dynon to look closer at it.

I know how I fixed mine but it should not be broadcast just yet as the Dynon folk do not need 30 different opinions on how to fix a problem in the field.

Cheers
DB:cool:

jthocker
02-23-2009, 06:36 AM
Dave,
I think that the servo's that came back from Dynon after the shear screw update had that "microscopic" play at the screw head. The servo's are working just fine with that "play".
Regards,

RV10inOz
02-23-2009, 03:22 PM
Thats good to hear Joe!

As you would know any accumulative backlash in a system will give rise to sloppy control.

Yes the amount of movement around the head is very small, however Dynon said .....
If there is any movement at all between these two
parts, your shear screw is loose and should be repaired per the following instructions.
However, slight movement of the ENTIRE arm/capstan/disc/shaft relative to the
internal gearing is expected.

So I take that literally!

Glad to hear its all going well for you! I can not wait to take this baby for a lap.

DB:cool:

RV10inOz
02-24-2009, 07:37 PM
News just to hand..............and makes more sense now!

We may need to revise the wording there. Its really the ability of the shear screw to move in its threaded hole that we want to eliminate. This effect is orders of magnitude worse than the normal manufacturing tolerance between the shear screw head and the hole bored in the arm to capture it.

All :):):)

Jamie
02-25-2009, 05:41 AM
For what it's worth, I now have an SV42 servo on the way to use as the pitch servo. I have not tried the sheer screw service procedure on my existing servo.

I am still having the pitch issue but after more discussions with Dynon we have a fairly aggressive agenda for figuring this thing out. Will report back with more details when I fly the SV42.

pierre smith
02-25-2009, 05:51 AM
.....that's under construction in my hangar and I just looked at the pitch servo carefully. It appears that the head of the shear screw is too small or the hole is too big...the reason for the slop.

Regards,

RV10inOz
02-25-2009, 02:42 PM
Piere

The folks at Dynon say that this is not a problem, compared to the movement you get from the shear screw being loose. If its loose the amount of rocking is quite likely to be considerably more that the clearance in the hole.

I have applied a very small amount of loctite, using the end of a paper clip, and only half of the drop the clip would hold, and run it around the outside of the head. Capilliary action takes it into the gap, and leaving it facing down so it does not go to the back and glue the arm to the disc I left it overnight. All slop gone. Of course I take the risk of it being harder to over power and break the shear screw, but using the very slight amount I used it would be unlikely to get any excess in the wrong place.

If you do this.....be very careful!

Some extra reading here for you.

http://dynonavionics.com/cgi-bin/yabb2/YaBB.pl?num=1235026530

jthocker
02-25-2009, 06:14 PM
Jamie,
I'm interested as to why you haven't tried the shear screw fix?
If for instance you get the new -42 servos, and Dynon has made sure those shear screws are tight,and you install them. Then flight test, and everything is wonderful, and then you report that here, what will everyone then know?
If on the other hand, you did the shear screw service, found the AP still oscillates, then replaced the servos and found it rock solid, that would be extremely helpful to everyone. But if you're totally fed up with your Autopilot and just want to get it fixed I certainly would understand.:D
In any case good luck and best regards,

Jamie
02-25-2009, 06:42 PM
The reason why I haven't done the sheer screw fix was simply because there was another problem with my servo. The calibration of the 'servo force' reading was incorrect, meaning that even with the airplane trimmed in pitch, engaging the servo would indicate a need a nose down trim. So basically I was going to have to return the servo anyway, so why even try? If I install the SV42 servo and the AP performance is good and time permitting I will perform the service instruction on the old SV32 servo and re-install it to give you guys another datapoint.

The reason I asked for an SV42 servo is because I'm suspicious about the SV32 servos having enough torque. The reason I say this is because with the servos engaged it takes very little force on the elevators (pressing on the elevators, not using the stick) to cause the servo to slip, even with the servo torque at 100%. I'm guessing it takes just a pound or two of force, but I'm going to try to quantify it for the Dynon folks just to give them more data.

Here's my question: The only reason for limiting available servo torque is to allow the user to override the servos in flight, right? Well, with the SV32 servos even at 100% torque it takes almost no force whatsoever on the stick to cause the servos to slip. So why not just use the more powerful servos to give us more range in available torque? In other words, the servo torque setting on my RV-7A with the SV32 servos is absolutely useless.

jthocker
02-25-2009, 08:04 PM
Jamie,
I noticed the same slipping as you, so I'll be very interested to see how these servos do. Keep us updated.
Thanks,

Slagergren
02-25-2009, 08:58 PM
Wow, would you go with Dynon again on the AP or simply step up to a Trutrak unit? I read all the threads on this and am a little concerned about my current planned decision to go w/Dynon's AP. Given all your troubles and effort I think Dynon needs to send a rep/tech out to inspect your plane, verify install then help you through this effort. I agree Dynon could always use more data collected (ie have you do more flying and possibly record some data) but come on lets verfy that the thing is at least installed correctly first. Given that there are so few of units out there in the first place I think they could user your positive reference. Based on what I read it sounds more like a software/ control algorithum issue. Nothing against Dynon but I think given all that you have been through they owe you a better answer/ support then to try and blame it on installation at this point. True product support and there by product improvement demands good root cause analysis no matter the situation. Dynon, yourself and us potnetial customer's will all benefit from this. As a potenital Dynon customer I would like to read a constructive/ happy resolution to this. Dynon's price point on their AP has me for now but I will continue to do some additional home work before making the final decision.

Hang in there and thanks for sharing,
Steve

Slagergren
02-25-2009, 09:09 PM
Looking for additional information Good and Bad about other RV pilots experiences w/Dynon's auto pilot units.

Thanks for any feedback

Brantel
02-25-2009, 09:11 PM
What is the normal size TT servo for an RV6,7,8,9? Is it a "B"?

If so TT rates their "B" at 30in/lbs but do not give at what radius, assuming 1" radius????

Dynon rates their "SV32" at 24in/lbs @ recommended outer hole.

Trio states most install in the outermost hole and that equals around 22.5in/lbs

Should be enough if the rating is real since the rest of the install is the same????

RV10inOz
02-25-2009, 10:54 PM
Slagergren

I have not flown the Dynon A/P yet however there are plenty of very happy users so that in itself says something at a very early stage.

There will always be some who have complaints, and usually its from their own errors not the product. In this case there are some problems that Dynon are addressing and pretty smartly I would say. many manufacturers of all sorts of goods bury their heads for months and never admit anything. These guys are different!

This is why we hinged our whole RV10 project on the Dynon system long ago. Time will tell for us in a couple of months, but I do expect a good result.

Having set up a Trio and a new S-TEC........ the Dynon looks like a good thing!

Cheers

DB:cool:

rvmills
02-25-2009, 10:59 PM
Jaime,

IMH(and non-expert)O, your decision to try the SV-42 sounds like a good course of action, based on the slipping you're seeing. Though you can move the servo rod to an inner hole (I know you know that), it sounds like the outer hole provides the best over-center protection, so stepping up to the -42 will give you the chance to up the torque and maintain that outer-hole oc margin...mo betta!

That being said, I was wondering if you saw the same slipping and DN trim annunciations in both the SV-32 servos you tried? (I think you said you were getting another one a while back...not sure if that ever happened.) Also, were you seeing a lot of, or any slipping in flight?

(Same question to Jon...your descriptions along the way have sounded similar to mine...did you see any slipping in flight, before and/or after the shear screw service was done?)

For comparison, in ground testing, done as you have described, I can make the servo slip with somewhat light force on the elevator. However, it sounds like it's not as easy to do as on yours Jaime. Breakout, or slip-inducing force with the stick sounds different as well...it's not hard to make it slip, but it's not "almost no force at all". Seemed to me to be about right...however, I don't have experience with other APs in my -6, so my "sample size" is very small! I'll talk to a 9A bud with a Dynon AP that we are working to dial in, and another 9A bro with a TT, and see if I can do a three way side-by-side comparison on those forces.

In flight, I don't think the servo has shown any slipping at all, even in somewhat bumpy air. Still working and testing it all, and will report the results of the shear screw service when that is done and fully tested. Feels like I'm getting closer to Jon's solid performance...will report back.

Wish we were closer so we could do a comparison, and it will be interesting to hear your observations with the -42 installed. It will also be interesting to see if, with the SV-42 at 100% Tq, the problem goes away, and then to see if you can step-down the torque setting and re-create the problem. That would be another good data point for all. Not trying to add to your test-card stack though! ;) Hmmm, thinking about it, perhaps that's something I can try as well...see if I can duplicate what you describe by lowering my Tq setting...once I get it dialed in...almost there! :)

Hope this does it for ya, and good luck!!

Cheers,
Bob

Jamie
02-26-2009, 06:27 AM
The first set of servos I had indicated trim perfectly. The second set has the invalid trim calibration indicating a need for nose down trim when the airplane is perfectly in trim.

In other words, even when I engage the servo on the ground, the EFIS immediately tells me to add nose down trim. The first servo did not do that. That is simply an instrumentation thing though and doesn't affect the logic (per Dynon) so it shouldn't be problem with flying the airplane, but it's certainly something that needs to be remedied.

Dynon has gone above and beyond to try to make me happy with this thing and I seriously don't have any problems with them. Heck, my day job is writing software that runs in unusual places as well, so I can sympathize with them completely.

If I am still struggling with this issue at Sun-n-fun they have promised to have one of their guys hook up with me and we'll go fly my airplane and I'll let them see first hand the performance of the AP.

My sticks are also very long in my airplane. I shortened them just enough to pass beneath the stock instrument panel. A longer stick certainly yields more leverage against the servo. Bob, how long are your sticks? I know that the -6 aileron bellcranks are different, but I believe the elevator bellcranks are almost identical, right?

rvmills
02-26-2009, 11:38 PM
Jaime,

Went out to the hangar today, and pulled the floor to check/adjust my aileron trim springs. While in there, I measured the control stick and did some AP breakout/slip force measurements at the stick and at the control surfaces. I used a borrowed spring guage (the kind with a rod that you depress or push with, and the tension is measured on a scale in pounds...not super-exacting, but pretty good ball-park). Did this first on my airplane, and then on Greg Arehart's -9A with a Dynon AP. Here's what I found:

Stick length (to top ot grip) on mine is 14" to the elevator pivot point, and 17" to the aileron push tube connections. Makes it about 10"-11" or so from the spar top (SWAG, forgot to measure this...just mentioned if you don't have the floors pulled up and you compare). The stick-top to panel-bottom gap is about 3.5" at the full fwd stick.

I did the breakout tests where my hand fits the grip, which is about 12" from the elevator pivot point. I first did the tests with the controls neutral, and the servos in ALT/HDG hold. Three tests in each direction (fwd, aft, left, right). Then I did the same tests in servo "test". My SV-32 servo torque is set to 100% (both pitch and roll).

I saw very consistent results at the stick. In all four directions, the servo slipped at about 6 pounds of pressure. Range was 5-7, but on 15 of 18 tries, it was 6.

At the control surfaces, I applied the pressure at the mid-span point of the aileron or elevator, just forward of the trailing edge. Breakout force on the elevators was 6 pounds, and it was 9 pounds on the ailerons. Probably more on the ailerons due to the shorter chord length versus the elevator.

On Greg's airplane, though his sticks are longer (story of my life...had to beat you guys to that punchline! :)), I measured them close to where I did the tests on mine. His breakout force at the stick was also consistently 6, with a 5-7 range. At the elevators it was 4 (maybe due to a bigger elevator on a 9?) and at the ailerons it was 9-10.

Pretty consistent results, albeit somewhat unscientifc. Possibly completely useless info, but it may give you something quantitative to compare to as you eliminate bogeys in this quest!

As far as the elevator bellcrank goes, I think they are similar/the same in the 6 and 7, though can't say for sure. The Dynon install guide has only one diagram for install of the 6,7,9 pitch servo, so it is likely that it is. I'll post the diagram, and then some early pix of mine, so you can compare. Also have a couple thoughts about the mechanical installation that might be trouble-shooting ideas. I'm sure you already have that aspect well in hand, but just have some thoughts...plz take them as a wingman covering your six! :)

Here's the diagram for the 6,7,9 pitch servo:

http://img218.imageshack.us/img218/9564/pitchservodiagram.jpg

Straight-on view of my pitch servo:
http://img218.imageshack.us/img218/1735/pitchservofrontstraight.jpg

Side view:
http://img11.imageshack.us/img11/848/pitchservoside.jpg

Please forgive the sloppy "poor-man's torque-seal" (fingie-polish)...since been cleaned up!

For those trouble-shooting thoughts:

On the side view, you can see where on first install, the nut on the rod-end bearing was very lightly rubbing on the bellcrank. Didn't damage metal, just rubbed primer (lightly re-coated since the pic was taken). I had to use some spacer washers to move the rod further from the bellcrank, and those can be seen in the front pic. Thought is to make sure that the rod, bolt head, or nut is not contacting or dragging on your bellcrank or the vertical fuselage/baggage wall support. If it is, would likely cause fits with the servo and the elevator. (Dan H and Mike S...this is the bolt I couldn't turn around per your recommendation, due to clearance...did the others, and thanks!)

On the front view, the space between the bellcrank halves gets a washer installed as you pass the bolt through the bellcrank. Was a pain to install, but a little fuel-lube "sticky" on the washer made it more workable, and I got lucky on the first try. If that is not there, I think it could cause crushing/closing of the gap, and perhaps some drag on the elevator system...maybe, maybe not.

You've probably already checked this too, but the securuty of the mounting bracket to the airplane is pretty key, and I used 6 rivets in the side and 3 through the bottom, and it turned out pretty stiff and taut. Movement there would mess up the servo's performance, for sure.

Just some thoughts. I hope the new servo drops in and alleviates all the issues! Best of luck, and looking forward to success for you!!

Cheers,
Bob

Jamie
02-27-2009, 05:32 AM
Hi Bob:

Those are some good numbers. I appreciate it.

I'm going to simply put a fish scale on my stick to see how many pounds of force are required to cause the servo to slip. I will hopefully get out tonight or tomorrow to do this. It's supposed to be crummy around here all weekend so I'm not sure if I'll get to fly it.

I did the same as you can spaced the pushrod bearing off the elevator bellcrank with washers. My washer is in place inside the bellcrank and the mount is very, very rigid.

Jamie

Jamie
03-01-2009, 05:51 AM
Here's the e-mail I sent to Dynon this morning:

I have some *very* interesting follow-up from my day yesterday at the hangar. Here's what happened.

As mentioned, the new servo was allowing 4 degrees of movement (+- 2 degrees) in the elevators. I got in the airplane with the servo in test mode started pushing and pulling on the elevator pushrod to see what I could see. Looking very closely I could see the servo arm slightly twisting. In other words, looking closely I could see the arm lifting off of the attachment disk.

I decided to go ahead and pull the arm to check the sheer screw. The first thing I noticed was that when I pulled the cotter pin, the castle nut was quite loose. Yes, I understand the need for this to be loose to allow the sheer screw to break more easily. However, the castle nut was not even finger tight. The sheer screw was definitely locked in place and was not loose at all.

So, I put the arm back on, this time following the service instructions of making the castle nut finger tight, then turning until the shaft hold lined up with the next slot. I inserted a new pin temporarily, and reconnected the servo->bellcrank pushrod and checked the elevator travel. Voila. Now the travel is down to just about 1.2 degrees. This is very good and is the best I have seen. So in short there was one and only one change, and that was tightening the nut on the shaft. Now when I engage the alt hold on the ground I can very clearly see every little move on the stick that is made. I have not been able to do this yet.

As a temporary test I replaced with nylon washer with some steel ones. Elevator travel was subsequently reduced to 0.8 degrees.

I am of course a software guy and not a mechanical engineer, but I believe what is happening is the nylon washer is compressing and allowing the arm to twist. The rod-end bearings will place a twisting load on the arm and this twisting load is increased when a longer bolt and spacer washers are used on the arm, which many folks are doing with the pitch servos. The path from the servo arm to the elevator bellcrank is angled, increasing the twisting load even more.

I believe my findings are consistent with other people performing the sheer screw service instruction and then seeing a marked improvmenent in performance. I believe the performance improvement can in large part be attributed to the tightness of the cast nut.

I will also perform this procedure on my aileron servo. Now when I engage the AP in test mode on the ground, I can *barely* move the stick forward and backward without slipping the servo, maybe 0.5 inches or so. The side-to-side movement of the stick is about 4 inches!

So my plan is to fly the airplane as-is for now (with the nylon washer and nut finger tight + one slot). I'm very hopeful with the alt hold. I will then perform the same procedure (tightening the caste nut finger tight + one slot) on the aileron servo to see how it performs.

Now if wx would just cooperate we could get somewhere. :-)

Hope that helps,
Jamie

rvmills
03-01-2009, 10:07 AM
Jaime,

I just found the same thing on my pitch servo (we must have the same maintenance schedule!). I just pulled my pitch servo arm to look at and service the shear screw, and I found a very similar situation. When I pulled the cotter pin from the castle-nut, the nut turned pretty freely in my fingers. No resistance at all to start it turning. I wasn't sure if the act of wiggling out the cotter pin loosened the castle-nut, but it just seemed a bit too loose to me.

When I discussed the torque requirements (max 4.5 in-lb) for the castle-nut with an A&P buddy, he remarked "heck, finger tight is about 5 in-lb" (caveat: that's an unscientific analysis, not gospel or a recommendation).

When I put it back together, I used the original parts (new cotter pin), and like you, went to finger tight, then to where the next slot lined up (took almost no torque), and it felt more secure than when I took it off.

Really windy here, so haven't tested it yet. Didn't see a marked difference in movement at the stick after doing the service, but I wasn't seeing quite the movement in the control surfaces or at the stick that you were...certainly not 4 inches in the side to side movement. More like the .5" (all directions) before slipping that you describe seeing now with your fore-aft movement. But it does feel better at the servo arm.

So like you, I'm very hopeful that the last of the small pitch oscillations I've seen will go away, and we'll have performance like Bill, Jon and others are seeing!

One thing (lesson learned) I'll pass along about roll servo performance. During initial tests, my heading hold would wander quite a bit. Looked to me like heading itself was wandering as well. So I did a compass cal, and it worked better, but not quite as well as NAV hold. Later, after one round of tweaking the mechanical set-up, I did another servo cal and compass cal, and noted that I had different MAG INT (Intensity) settings on the D100 and D10A, though MAG INC (Inclination) matched. I matched them up, but used the wrong value (50-50 chance, as I didn't bring my notes to the compass rose that day, and I chose poorly!), and HDG hold went back to wandering. Rechecked (via the link on Dynon's site) for the proper value, set both EFISs to the correct value, and HDG hold now works like a champ, as does NAV hold. So, a difference in compass settings between the units may have been responsible for minor HDG wandering, but it looks like an incorrect setting (my MAG INT was pretty far off) will really cause issues with HDG hold! Just thought I'd mention it as you dial in both of your servos.

Good luck with the flight testing!!

Cheers,
Bob

breister
03-01-2009, 12:15 PM
Since it was asked earlier, I'll mention that 1 inch pound equals a force of 1 lb acting on a lever 1" long.

If you're only seeing 8 lbs or so (at the servo 1" out from the center) before slippage, then the servo isn't providing the advertised torque. If the distance from the center is 2", then 8 lbs = 16 inch-pounds, which is closer.

And, just to steer off any bad jokes, yes, length matters...

rvmills
03-01-2009, 12:46 PM
Since it was asked earlier, I'll mention that 1 inch pound equals a force of 1 lb acting on a lever 1" long.

If you're only seeing 8 lbs or so (at the servo 1" out from the center) before slippage, then the servo isn't providing the advertised torque. If the distance from the center is 2", then 8 lbs = 16 inch-pounds, which is closer.

And, just to steer off any bad jokes, yes, length matters...

Bill,

Not sure if you're referring to the breakout/force-to-slip measurements I took, but if so, just to clarify, those measurements were taken at the stick grip and at the center of the trailing edges of the control surfaces. So they weren't really designed to measure the actual servo torque at the slip point, but rather to give Jaime (or others) a point for comparison in how easily his servos slipped with pressure on the stick (or surfaces).

Your calculations on torque values are of course correct. I applied pressure at 12" up the stick, so the torque applied to the elevator pivot point to slip the servos was in the 'hood of 6 foot-pounds. With all the mechanical advantage of the control system, I'm sure that's far more than was being exerted at the servo arm. Might be a way to sleuth that all out, but it's been a long time since I took physics! ;)

I didn't have the tail open when I did the tests, but it would have been interesting to see what the force required at the outer hole would have been (though my servos don't slip at all in flight, so the outer hole at 100% torque works well!)

Hopefully our next test flights will show it's not a torque issue at all! :)

Cheers,
Bob

rvmills
03-06-2009, 12:03 AM
With Greg Arehart in the right seat, we launched to wring out the Dynon AP in my 6 today. We were both impressed by the performance after servicing the pitch servo per Dynon's instructions (aided by the posts here...thanks much!).

Wx was good (and cold...38F at the airport and 15F at 12.5K). Air was mostly smooth, with very intermittant light chop up high, and some very light turbulence down low. Tests run at WOT, 2300 RPM, 165 KIAS/197 KTAS (eased the throttle a bit to maintain the same speed in descents for testing).

At 12.5K altitude hold was very solid...+/- 10', an occasional excursion to +/- 20', with small 50-100 fpm corrections shown on the VSI (almost insignificant, and we had to be watching it to see the excursions). Turns, both during heading bug commanded turns and NAV tracking turns, also showed very solid altitude hold, same parameters. Pitch corrections were for the most part unfelt, with occasional slight "bumps" felt in the seat of the pants (and we attributed most of those to times when the air wasn't quite smooth).

Descents, both straight ahead and in turns, showed the same, mostly smooth corrections. With the Dynon internal climb/descent preset at 500 fpm, each 500 feet of descent took 1 minute +/- 1-2 seconds. VSI showed 500 fpm, +/- 150 fpm (most of the time), with greater VSI excursions being attributable to bumpier air as we descended. Both level-offs were smooth and right on the selected altitude.

Started out with pitch sensitivity at 15, and adjusted down to 14 for the lite chop, and it handled quite well throughout (except for that one big bump that caught us by surprise and had us laughing!)

Roll performance was equally good, with heading hold solid (+/- 1-2 deg), turns being smooth (with the occasional aileron bump...moved the roll sensitivity from 8-7, and it did well), and roll-outs being on target with no hunting noted. 180 deg turn feature and NAV tracking also checked out quite well.

It was a really pleasing test flight, and thanks Greg for riding shotgun! Your 9A Dynon AP test hop is next!

Good stuff! :)

Cheers,
Bob

breister
03-06-2009, 08:22 PM
One other thought for pitch-sensitive problems.

Be aware that the autopilot doesn't care what your actual altitude is, so if you were to disconnect it from the static system and simply use cabin air it would still work.

That may actually be advantageous in our airplanes, as some static systems are "accurate" but have small lag or other changes they sense with pitch which can be "magnified" at the autopilot. In my prior plane with a competitor's autopilot, switching from the static ports as static source to cabin air resulted in markedly smoother pitch changes and leveler altitude hold.

Sam Buchanan
03-07-2009, 06:52 PM
One other thought for pitch-sensitive problems.

Be aware that the autopilot doesn't care what your actual altitude is, so if you were to disconnect it from the static system and simply use cabin air it would still work.

That may actually be advantageous in our airplanes, as some static systems are "accurate" but have small lag or other changes they sense with pitch which can be "magnified" at the autopilot. In my prior plane with a competitor's autopilot, switching from the static ports as static source to cabin air resulted in markedly smoother pitch changes and leveler altitude hold.

Just be ready for some altitude excursions when you open an air vent! :)

(Found this out when I unknowingly had a loose static connection on a test flight)

RV10inOz
03-07-2009, 09:30 PM
My thoughts too :eek:

Better to fix your static problems!

breister
03-08-2009, 01:34 PM
Just be ready for some altitude excursions when you open an air vent! :)

lol - yeah, I forgot about that!

It's been a few years since that airplane. Just disengage autopilot when changing the vents!

(Found this out when I unknowingly had a loose static connection on a test flight)

Exactly - I had a problem when my static line developed a leak and ingested a bunch of water, which is why I switched to cabin static. That was when I noticed how much smoother the AP was on cabin air. It was months later (and warmer) when I first opened a vent in flight.

YEE-hah!!!!

User beware! :)

flickroll
03-16-2009, 06:02 PM
Here's the e-mail I sent to Dynon this morning:

Jamie, what was Dynon's response to you email? I'm about to permanently attach my wings and it's a lot easier tweaking the servo before the wings go on. Did they agree with your nut tightening method?

Brantel
04-07-2009, 07:14 AM
Hey Jamie,

Any updates on your pitch servo issues? Did you try the larger servo????

Jamie
04-07-2009, 07:24 AM
Hey Jamie,

Any updates on your pitch servo issues? Did you try the larger servo????

Hi Brian:

Yes, I tried the larger servo. No luck. It was about the same as before...it would (sort of) hold altitude but it wasn't smooth at all. I have some more verbose updates and I will post as soon as I have a few minutes (hopefully later today).

rvmills
04-07-2009, 08:37 PM
Hi Brian:

Yes, I tried the larger servo. No luck. It was about the same as before...it would (sort of) hold altitude but it wasn't smooth at all. I have some more verbose updates and I will post as soon as I have a few minutes (hopefully later today).

Sorry to hear that Jaime. Was hoping that "no news was good news", and you were just busy doing cool stuff like flying special kids around (that was a great story)! Interested to hear your results, scratching my head for a vicarious solution, and sure hoping for the best!

Cheers,
Bob

Jamie
04-11-2009, 08:29 PM
See here (http://www.vansairforce.com/community/showthread.php?p=317243#post317243) for my update.

647jc
04-12-2009, 08:32 AM
Jamie,

When on the ground with the AP engaged do you see any of the slop in the control surfaces that you saw with the Dynon AP Servos?

Jamie
04-12-2009, 03:11 PM
Jamie,

When on the ground with the AP engaged do you see any of the slop in the control surfaces that you saw with the Dynon AP Servos?

I see less movement with the Trutrak than the Dynon -- less than 1/2", although it's a little more difficult to quantify with the Trutrak because there's no way to engage the pitch servo without it moving.

breister
04-12-2009, 10:12 PM
I see less movement with the Trutrak than the Dynon -- less than 1/2", although it's a little more difficult to quantify with the Trutrak because there's no way to engage the pitch servo without it moving.

Try this: Engage the AP on the ground and observe whether the steering is commanding nose up (climb) or nose down. If nose up, set a descent rate of 100fpm. Play with it a few times between alt hold and +/- 100fpm, and it usually settles down.

The one I can never get to be solid is heading mode - it's always "click-click-clicking" one way or the other.

Jamie
04-13-2009, 07:34 AM
Try this: Engage the AP on the ground and observe whether the steering is commanding nose up (climb) or nose down. If nose up, set a descent rate of 100fpm. Play with it a few times between alt hold and +/- 100fpm, and it usually settles down.

The one I can never get to be solid is heading mode - it's always "click-click-clicking" one way or the other.

I have the "straight" Digiflight II, which only does altitude hold, so I can't command a decent or climb.

breister
04-13-2009, 09:41 AM
I have the "straight" Digiflight II, which only does altitude hold, so I can't command a decent or climb.

Ah - well, in that case save your pennies! Last I heard they will upgrade for only the cost difference, and as I posted elsewhere you can simulate a REALLY smooth precision approach by "dialing in" the right descent rate. The swap-out is painless as it does not require any re-wiring.

Note: In your case you would only upgrade to the VS because your GPS does not provide ARINC GPS steering.

It would be nicer if they had a comparison grid on their website for product/feature. They used to, but I can't find it anymore.

Cheers,

Bill

TrutrakTech
04-13-2009, 09:52 AM
Ah - well, in that case save your pennies! Last I heard they will upgrade for only the cost difference, and as I posted elsewhere you can simulate a REALLY smooth precision approach by "dialing in" the right descent rate. The swap-out is painless as it does not require any re-wiring.

Note: In your case you would only upgrade to the VS because your GPS does not provide ARINC GPS steering.

It would be nicer if they had a comparison grid on their website for product/feature. They used to, but I can't find it anymore.

Cheers,

Bill

http://www.trutrakap.com/autopilot2_2.htm

Not completely up to date, but I think it's what you were looking for.

breister
04-13-2009, 11:39 AM
http://www.trutrakap.com/autopilot2_2.htm

Not completely up to date, but I think it's what you were looking for.

Yep, that was it! Navigation is a bit less obvious than it used to be (probably several years back, I'm dating myself).

I had a difficult time locating it at the bottom of the home page. You may wish to consider adding "feature cross-reference" as an entry in the FAQ's page and / or add a line entry on your "Products" page similar to the line entry for "EFIS Pricing/Features" near the top.

Cheers,

Bill

TrutrakTech
04-13-2009, 11:44 AM
Yep, that was it! Navigation is a bit less obvious than it used to be (probably several years back, I'm dating myself).

I had a difficult time locating it at the bottom of the home page. You may wish to consider adding "feature cross-reference" as an entry in the FAQ's page and / or add a line entry on your "Products" page similar to the line entry for "EFIS Pricing/Features" near the top.

Cheers,

Bill

We are working on getting client editor software here so we can make changes to our own website. As it is right now, it's pretty difficult because we don't host our own site we have to send all changes to the webmaster. It will get better, I promise!