What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Dynon AP "Asks" For Nose Up Trim

Toobuilder

Toobuilder

Well Known Member
Just started flying this AP, so forgive if this is a common issue. I can trim the airplane for nice hands off level flight in smooth air, but when I engage the autopilot, the display indicates it's out of trim and needs nose up. I can trim it up until the indicator light goes out, but when I turn off the AP, the airplane is way out of trim nose high. It seems the AP doesn't know the airplane is in trim.

Is there an adjustment to tune this behavior out?
 
I have this happen too. Sometimes the amount of unneeded up trim is surprising when I disconnect the AP.
I look forward to Dynon's or others answer.
Thanks for asking the question.
 
I assume you have the limiting bracket installed on the servo the prevents the possibility of the arm going over center. If that is correct, then it is likely the bracket has become magnetized. If the bracket or the two screws used to install it are magnetized it will cause that behavior. Most RVs don't really need the bracket as our control system limits the arm movement well within a safe range, but that is something each builder should determine. If you feel you need the bracket, see if you can get it demagnetized and that should fix the issue.
 
MelJordan said:
I assume you have the limiting bracket installed on the servo the prevents the possibility of the arm going over center. If that is correct, then it is likely the bracket has become magnetized. If the bracket or the two screws used to install it are magnetized it will cause that behavior. Most RVs don't really need the bracket as our control system limits the arm movement well within a safe range, but that is something each builder should determine. If you feel you need the bracket, see if you can get it demagnetized and that should fix the issue.
Click to expand...

I did leave out the limiting bracket...
 
Well, they are on the forum, so I would have expected an answer from them if nobody else had direct answers.

Also, I know of one other airplane exhibiting the same behavior - but no limiting bracket installed. Evidence suggests that the presence of the limiting bracket is not the root cause.
 
I experienced the same issue. Both of my SV32 servos eventually failed, but I can't say for certain if it was related. If I remember correctly, the pitch servo eventually started reporting that it was slipping constantly, and it was exerting very little force on the control system. Torque was set to 100. Dynon replaced both of my servos with SV42 units and I experienced no further issues.

Aside from the failures, If I were to build another 9 I would go with SV42 servos from the start. The SV32 units were always slipping when it was bumpy. You can always dial down the torque on the 42s.... I think they're about 1lb heavier.
 
Considering how heavy the Rocket is in pitch when solo, I do have the 42 installed there. This servo will keep the nose up, even in a hard turn. And yes, torque is set to 100%

However, this condition exists when the airplane is trimmed for hands off flight and calm air. The servo is hardly working at all, so should not be slipping.
 
Toobuilder said:
Considering how heavy the Rocket is in pitch when solo, I do have the 42 installed there. This servo will keep the nose up, even in a hard turn. And yes, torque is set to 100%

However, this condition exists when the airplane is trimmed for hands off flight and calm air. The servo is hardly working at all, so should not be slipping.
Click to expand...

I changed the geometry of my elevator bellcrank to balance the pitch forces in my rocket. Worked extremely well, but it does require more stick throw.

I use an SV32 and get the trim alerts as well. It may be due to the control sensitivity of our rides at high speeds. I will try turning the gain down.
 
Last edited:
I also changed the bellcrank geometry since I had it out and on the bench. I took 1/2 inch off the output arm to help the leverage a little.
 
Sorry this took a few days for us to notice. We don't stick our noses in the autopilot section as often as we should.

We do have some reports of trim indications not being as accurate as they should. Unfortunately, this isn't user adjustable. However, the good news is that we have been testing an updated trim detection algorithm, which seems to work very well, and should fix this issue with a simple software update. We expect to have this update in the next software version.

So for now, if you are having the issue, all we can tell you is to ignore the alerts for now. It's not indicative of any broken hardware.
 
Mike,

Thanks for bring this issue up, as you know I am having the same issues. I look forward to Dynon's software update!!
 
The release we are working on currently is for SkyView only, in order to see if it is an effective improvement. If it works, we will discuss upgrading D10/D100 products.
 
I flew a two hour round trip yesterday using the new AP program. Testing the results I found the pitch in perfect trim each time I disengaged the AP.

But it seems now that the altitude struggles to hold steady. I was cruising high in smooth air but several times a small bump would cause the pitch to hunt, up and down about 5 cycles 50 feet or so before settling. Also when I dialed in an altitude change either up or down it would overshoot the 500FPM then overshoot the new altitude starting the hunt again. Before this new program the pitch was rock steady.

Do you recommend any setting changes, or other thoughts?
 
Bruce,
The code was only supposed to change the trim detection, so I don't have an obvious reason that it would change the actual performance of the autopilot at all. I have our AP expert looking into it.

Thanks for the feedback on trim performance. We're getting good feedback on that so it looks like positive change.
 
Bruce, that would be an undocumented design feature.

I am getting the trim indications that are annoying, but until the code is stable I will put up with the flags not the ride. ;) Thanks for Beta testing! Having done some before it can be fun!
 
BruceEicher said:
I flew a two hour round trip yesterday using the new AP program. Testing the results I found the pitch in perfect trim each time I disengaged the AP.

But it seems now that the altitude struggles to hold steady. I was cruising high in smooth air but several times a small bump would cause the pitch to hunt, up and down about 5 cycles 50 feet or so before settling. Also when I dialed in an altitude change either up or down it would overshoot the 500FPM then overshoot the new altitude starting the hunt again. Before this new program the pitch was rock steady.

Do you recommend any setting changes, or other thoughts?
Click to expand...

Hi Bruce,

Thanks for trying the trim fix out. Were you getting any pitch SLIP indications when it was misbehaving?

Other things being equal, my recommendation would be to run the airspeed hold portions of the autopilot tuning guide (here: http://www.dynonavionics.com/downlo...ew_Autopilot_In-Flight_Tuning_Guide-Rev_B.pdf) I'd also double check for any slop between the elevator and the servo.

We'd like to get a copy of the dynon diagnostic log for that flight, if that's possible. You can get in touch with us at [email protected]; please put it to my attention.

Thanks,
Lawrence Doan
Autopilot Guy
 
dynonsupport said:
Hi Bruce,

Thanks for trying the trim fix out. Were you getting any pitch SLIP indications when it was misbehaving?

Other things being equal, my recommendation would be to run the airspeed hold portions of the autopilot tuning guide (here: http://www.dynonavionics.com/downlo...ew_Autopilot_In-Flight_Tuning_Guide-Rev_B.pdf) I'd also double check for any slop between the elevator and the servo.

We'd like to get a copy of the dynon diagnostic log for that flight, if that's possible. You can get in touch with us at [email protected]; please put it to my attention.

Thanks,
Lawrence Doan
Autopilot Guy
Click to expand...

Hi Lawrence,

No servo slip.
I will download the log tonight, check for linkage slop and take a peek at the tuning guide PDF.
We fly to Montana this holiday weekend so I will gather more data I'm sure.
Thank you.
 
Problem solved

Dynon as always stepped up and took care of the issue. Lawrence read my flight data and saw servo or linkage slop. The servo was the problem, mailed it in and repaired, back in a week, No charge. Now the altitude is rock steady, and the trim is accurate.

Thanks Dynon!

FYI, before the new public beta trim program, we believe the out of trim condition kept a load on the servo, thus taking out the lash/slop. The new program lets the system relax in-trim. So it might uncover further linkage or servo slop in other's...YMMV....

So far I would recommend the new trim program...
 
Last edited:
Apologies - AP newbie question

My AP has been working perfectly in Simplified Mode since new. It held altitude, climbed and descended to target altitudes perfectly and controlled, it did everything I hoped for.

I updated to 10.2 and now it won?t do any of the above, won?t hold altitude it fly?s like a porpoise, and descends erratically ie it wont descend at a constant rate. In Roll the AP is ok, Pitch is next to useless.

To fix this new problem, Dynon has suggested I refer to the Autopilot In-Flight Tuning Guide, see extract below.

In particular, if the autopilot cannot keep up with the flight director pitch command bar, PITCH SENSITIVITY should be increased. At some point the AP will track the command bars, but follow behind them.

My question is where or what are the "Command Bars" ?
 
You need to change the main efis display to "flight director" presentation. Then you will see two inverted 'V' s replacing the dot and bars of the conventional display. The Vs represent the wings, the vertex is the nose. One of the Vs will move with the airplane, just like the AI; the other V is the "command bar", and shows where the box thinks the plane should be. When hand flying you nest the Vs together. The autopilot should do the same.
 
Thanks Bob.

Here is a photo of what I'm seeing. Im guessing Ive got the V's nested ?

 
Last edited:
Derek,

Yes, those are the 'airplane' and command bars nested together.

As you turn up PITCH SENSITIVITY (and later PITCH GAIN if you need it) be sure to turn it the minimum necessary to achieve the performance you're after. As you get close to the right setting, the improvement becomes softer as you increase gains, and it's possible to over do it.

Feel free to get in touch with us at [email protected].

Lawrence Doan
Autopilot Guy
 
Dynon Support,

I was about to buy a couple of SV32 servos and use my D100 as an Autopilot. I was concerned that you are not committed to porting these fixes to the D100 series. Can you confirm Dynon's plan here?

Also, based upon this thread, will the SV32's be adequate for pitch and roll on the RV-6?

Thanks,

Larry
 
Are SV32 servos adequate?

Thread revival:

I was hoping to see a conclusion to the question Larry posed because this is the final step in my decision making before palcing an order for some Dynon gear.

In the various threads on the subject it appears opinions are divided on the adequacy of the SV32 servos in an RV, in my case a 6 with manual trim. Given the SV42 servos are the same size and price would it not be worth the small weight penalty to select the stronger servos to eliminate the question of adequacy?

Thanks
Mal
 
I have found in my -8 the 32 servos to be just fine. When they do slip it is because I have either done something wrong, like turned the trim knob the wrong way, or I am in heavy turbulence and should not be on auto pilot anyway. I have factory default settings...ymmv....
 
I have about 180 hours on my 6 now and have never seen a slip indication with my -32 servos. That said, I haven't flown a lot in significant chop with the AP engaged.

Larry
 
My original -32s...

...could not complete the pre-fliight calibration test...the one where it's supposed to move the controls UP/LEFT, then DOWN/RIGHT. The pitch servo just chattered and chattered. My elevator is perfectly balanced.
I had to send in my SV screen for error codes, so asked for a -42 servo at the same time.
Now, my new SV-Touch is GREAT!!!...and my AP works pretty darn good. There's just a small twitch or "pulse" in the pitch, but I can only feel it in the stick...not the plane, so I think it must be "slop". I'm almost done with Phase I...about 35 hours.
The -32 to -42 upgrade was done 'gratis' by Dynon. :D
 
My Trutrak pitch servo was doing something similar. Trutrak had me send it in. They fixed the problem for me. John
 
You must log in or register to reply here.
Back
Top