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Rascal R/C Ground Yawing

Designing a stable autopilot is one of the hardest things. Need help?

Rascal R/C Ground Yawing

Postby aleksey » Tue Jan 17, 2017 1:39 am

Hey everyone,

I hope this is the right place for the post as I believe the problem I'm seeing is tied with the autopilot / route manager.

I downloaded the Rascal R/C model from the official FlightGear hangar a couple of days ago - I'm using the JSBSim model in that folder. When I launch the Rascal 110 JSBSim aircraft, it starts turning on the ground as it appears to be seeking some kind of marker. It then oscillates as if it is trying to converge on it. So as an example, if you launch the simulation, Rascal starts out on a runway, bu then yaws left 270 deg. If I give it power, I can push it through to a take-off, but it will be off the runway.

Everything seems to be OK (and as expected) as soon as I get it in the air, so it appears that something is going on right away during start-up. I looked through all the directory files and tried playing deleting the fcs just to see what it does, but nothing looks to be making a difference.

Appreciate any help on where I should be looking in the files - I'm sure this is something obvious :)

Aleksey
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Re: Rascal R/C Ground Yawing

Postby aleksey » Tue Jan 17, 2017 1:58 am

Here is a quick video screen capture of what I'm seeing.

https://youtu.be/AQS9fXR2vh0

Appreciate any thoughts.
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Re: Rascal R/C Ground Yawing

Postby curt » Tue Jan 17, 2017 2:23 am

I'm pretty sure it's weather-vaning into the wind. Never could figure out how to make the jsbsim gear more 'sticky' for itty bitty aircraft like this. I usually wait for the wind and aircraft to settle before launching. Depending on what I'm doing and how patient I am I might pick the best runway ... FlightGear used to do that automatically, but I'm not sure the startup ordering gets that right all the time these days. My external autopilot (https://github.com/AuraUAS) will do auto-take off but needs to be mostly into the wind. I don't have a flying rascal right now, but I have a senior telemaster that's kind of similar, just a bit smaller wing span, but almost the same weight. The real telemaster actually handles cross wind takeoffs much better than the simulated rascal ...
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Re: Rascal R/C Ground Yawing

Postby aleksey » Tue Jan 17, 2017 3:09 am

Thanks for the thoughts curt - awesome video footage by the way!

I tried turning off the wind in the simulator as well as changing airports (and having FG put me on a favorable runway), but it looks like the problem is still there.

Below is the video of what this last attempt looked like.



I'm going to try some of the basics: calibrating joystick, turning joystick off, and switching OS systems to see if the problem persists. Let me know if there are any other thoughts.
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Re: Rascal R/C Ground Yawing

Postby curt » Tue Jan 17, 2017 12:27 pm

I"m still saying it's the wind causing the heading change on the ground. Also, the try maybe taking off with just a few notches of throttle rather than full throttle and see if that helps. Engine torque relative to gear stickiness is probably way out of whack on this model. The original I was modeling was so overpowered it would be airborne before the engine could run up to full throttle, but it's gear didn't slide laterally like in JSBSim. It was also fast ... we clocked it at 100 mph on once pass. I was trying to match that kind of performance.
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