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03-25-2016, 08:57 AM
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Join Date: Jun 2014
Location: Ottawa, ON, Canada
Posts: 353
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Quote:
Originally Posted by jdeas
Not so, I have benn flying with a distributed power,trim and flap system for the last few years based on CAN. AIRINC 825 and CANaerospace specs are out there.
Here is the paper I presented at Osh a few years back.
http://jadsystems.com/CANaerospace_OSH_2009_Paper.pdf
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I know CAN is used, I meant the scheduling model ... most applications I've seen so far do NOT use the fully deterministic, real-time, scheduling model, but instead just put data on the bus at a slow enough amount that no major contention is expected (The main model I've seen is described in ARINC 825).
I was playing around with a way to schedule and program things to have each node putting things on the bus with fully deterministic timing ... turns out the chipset I used didn't support it ... it's been a while since I played with that though ...
EDIT: There's also the MGL published specs on their CANBus config ...
__________________
J.F.
Sling 4 empennage kit on order!
Future EAA 245 Member (Hopefully)
Current Piper Warrior PA-28-151 Owner/Pilot
Ottawa, Ontario, Canada
http://www.sling4.ninja
Last edited by kamikaze : 03-25-2016 at 09:02 AM.
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03-25-2016, 09:08 AM
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Join Date: Mar 2006
Location: SoCal
Posts: 626
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real time can
RT automation on CAN is not difficult. I use markers and timeslots in some other designs but it wasn't really needed given the low data rates for the average GA aircraft
__________________
JD
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RV-7 N314SY (KWHP)
IO-360-B1B
CANbus based trim/flaps and electrical
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03-25-2016, 09:49 AM
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Join Date: Jan 2005
Location: Victoria, Canada
Posts: 2,251
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Quote:
Originally Posted by Ebbe
Rob,
there are considerable savings to make here. But the driving force for me has always been to have full control over what's going on. Features, looks, ergonomics. Not to mention the shear fun of it.
I'm still debating whether to take it to a commercial level, or just let it all out in the public domain. I wonder what the vote would be here on the forum....
- Ebbe
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Hi Ebbe. Awesome work. There is, in fact, a clearing house for open source avionics. MakerPlane provides open source avionics, kits and assembled. products. I licensed my avionics products to them under open-source hardware licensing and I receive a modest royalty on kitset and product revenue.
There is an ongoing open-source EFIS project that is applicable to what you are doing.
__________________
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V e r n. ====
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RV-9A complete
Harmon Rocket complete
S-21 wings complete
Victoria, BC (Summer)
Chandler, Az (Winter)
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03-25-2016, 10:33 AM
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Join Date: Feb 2016
Location: Knoxville, TN
Posts: 26
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Quote:
Originally Posted by jdeas
Not so, I have benn flying with a distributed power,trim and flap system for the last few years based on CAN. AIRINC 825 and CANaerospace specs are out there.
Here is the paper I presented at Osh a few years back.
http://jadsystems.com/CANaerospace_OSH_2009_Paper.pdf
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Jim, that's an interesting application you did. Yes, the CAN bus utilization in my case is very low, a few percent at most. And of that, only a fraction is "unsolicited", meaning not initiated by pilot action such as interacting with the user interface. Latency is certainly not a concern here.
- Ebbe
__________________
RV-7A, purchased from builder
IO-360, ~450 hrs
Avionics: own design
KMMI - Athens, TN
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03-25-2016, 11:21 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by Brantel
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+1!!!!!!!!!
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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03-25-2016, 11:36 AM
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Join Date: Feb 2016
Location: Knoxville, TN
Posts: 26
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Quote:
Originally Posted by Kevin Horton
Wow! You've certainly raised the bar on designing your own panel
How well does the AHRS work? Do you use pitot/static or GPS inputs to stabilize the attitude algorithm, or does it manage to maintain stability without any assistance? How well does it realign in flight, if needed?
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Hi Kevin,
oh, boy, could I use a seasoned test pilot of your caliber when testing the autopilot... Having a newly put-together piece of electronics take over the control stick is unnerving.
Yes, the AHRS uses aiding for long-term correction. This particular IMU is not in any way aviation grade, I first got it for experimental purpose. But it had remarkable low noise and good stability, even over large temperature range. Much better than I expected. Introduce the vibration during flight, things deteriorate quite a bit. With turn rate from GPS, and TAS from the airdata, bank is held very accurate. I believe it's the accelerometers more than the gyros that suffer from vibrations. My future, second, AHRS will use a higher end IMU that would need much less "trickery", and maybe even provide acceptable position data for an extended time of GPS outage.
- Ebbe
__________________
RV-7A, purchased from builder
IO-360, ~450 hrs
Avionics: own design
KMMI - Athens, TN
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03-25-2016, 01:45 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Quote:
Originally Posted by Ebbe
Hi Kevin,
oh, boy, could I use a seasoned test pilot of your caliber when testing the autopilot... Having a newly put-together piece of electronics take over the control stick is unnerving.
- Ebbe
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At least the software engineer of your autopilot is exceptionally motivated to design a safe system
I assume that the autopilot servos are sized so you can overpower them if required. If not, you should chose different servos, or add some sort of slip clutch between the servos and the controls.
Another thing to think about is the means to disconnect the autopilot. If your normal disconnect switch is working via software, it is wise to have a means to easily kill the electrical power to the servos, in case the software disconnect doesn't work.
Do you have any envelope protection in the autopilot? I.e. maximum and minimum airspeeds that it will stay within, g limits, AOA limits, bank angle limits, etc? If so, it is useful to do the initial testing of the envelope protection with the limits set to values well within the aircraft envelope - e.g., if the max airspeed envelope protection is intended to be at 200 kt TAS, do the initial testing with it set to 180 kt TAS. Once you have validated it works correctly at 180 kt, then reset the threshold to 200 kt for the real test.
Good luck with the testing. If I ever end up in the Saint Paul area, I'll try to track you down (my wife grew up in Green Bay - maybe we'll come up for the Vikings/Packers game).
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03-25-2016, 04:08 PM
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Join Date: Feb 2016
Location: Knoxville, TN
Posts: 26
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Quote:
Originally Posted by Kevin Horton
At least the software engineer of your autopilot is exceptionally motivated to design a safe system
I assume that the autopilot servos are sized so you can overpower them if required. If not, you should chose different servos, or add some sort of slip clutch between the servos and the controls.
Another thing to think about is the means to disconnect the autopilot. If your normal disconnect switch is working via software, it is wise to have a means to easily kill the electrical power to the servos, in case the software disconnect doesn't work.
Do you have any envelope protection in the autopilot? I.e. maximum and minimum airspeeds that it will stay within, g limits, AOA limits, bank angle limits, etc? If so, it is useful to do the initial testing of the envelope protection with the limits set to values well within the aircraft envelope - e.g., if the max airspeed envelope protection is intended to be at 200 kt TAS, do the initial testing with it set to 180 kt TAS. Once you have validated it works correctly at 180 kt, then reset the threshold to 200 kt for the real test.
Good luck with the testing. If I ever end up in the Saint Paul area, I'll try to track you down (my wife grew up in Green Bay - maybe we'll come up for the Vikings/Packers game).
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I wonder how common it is for the control engineer to be strapped on to the system he is tuning...
The servos can fairly easy be overridden, even with the torque setting at the highest value. As soon as I had the servos installed a few years back, I actually tested them with a very rudimentary controller hooked up to a commercially available AHRS -- of not so good quality. In fact it had a bug giving momentary erroneous roll data, which caused my controller software to command close to 100% aileron deflection. At cruise in the RV, it rolled fairly quickly to 90 degrees before I overpowered the servo. Right about that point, I realized that envelope protection would be a great idea.
I have limits to bank, pitch, min and max airspeed that are very conservative since it will be used for instrument flight, which means very gentle flying. Also excessive sink rate will disconnect, but I guess that would be because of an "upstream" software error. No AOA sensor (yet). Also, at the very output I limit the allowable servo deflection to maybe half of the available span -- past those limits would only be used in aerobatic flight, or at very low airspeeds.
There are several ways to disconnect. Disengage switch on stick, and front panel controls, which are software. Power switch to the servos, with a cap color that stands out in the row of switches. Then there is the CB to the servos. Lastly a soft iron shear bolt on the servo arm, which I really hope will never come into play.
- Ebbe
__________________
RV-7A, purchased from builder
IO-360, ~450 hrs
Avionics: own design
KMMI - Athens, TN
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03-25-2016, 06:43 PM
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Join Date: Sep 2012
Location: Omaha, NE (KMLE)
Posts: 2,247
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Quote:
Originally Posted by Ebbe
I wonder how common it is for the control engineer to be strapped on to the system he is tuning...
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I don't know, but I have always thought it should be a requirement.
__________________
Dale
Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
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03-26-2016, 10:07 AM
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Join Date: Nov 2009
Location: Boston
Posts: 154
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Ebbe, I love what you've done and it seems to be leagues above amateur level. Arguably, the engine monitoring system is the single most important avionics to promote safety and reliability of a flying experimental aircraft. Yet, even the non certified EMS units out there are far more expensive than I think they need to be. So, my question is that given your experience with your DIY EMS, how inexpensively could such a system be built? If you were going to open source any of your components, my priority interest would be for an EMS (that can also record the channels).
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