Trex450 loiter testing using Arducopter 2.0.50Beta

This video is of some loiter testing I did this morning of my Trex450 running the latest arducopter code, 2.0.50.


If it were a quad I might not be super happy with the results but for a traditional heli, I think this is a pretty good performance.  The altitude hold is very solid using Jason Short's latest code paired with a  maxbotix MB1260 XL-EZL0 sonar which is mounted on the tail using a custom 3d printed mount.


There's some more work to do to resolve the circling (which is always in the clockwise direction by the way).  I guess what's happening is that the heli is always missing it's target - so for example if the loiter point is straight north, it's actually heading slightly north-west.  I suspect the problem is either:

  1. the compass declination is incorrect
  2. it's caused by the natural interaction of the roll and pitch on the heli.  So for example if the autopilot wants the heli to go forward it pitches forward, but pitching forward also causes a slight roll left which we current don't account for in the code. 

Also the P and I values need some more tuning to stop any overshoot.


This code is the latest and greatest and can be downloaded from the APMissionPlanner.  By the way, if you're not familiar with the arducopter code for the heli, it's 95% the same as the quad code, just some changes here and there to deal with moving servos around instead of motors.

If anyone has any other ideas, comments or advice on the circling or anything else, I'd love to hear them.

Views: 730

Comment by Jason Short on October 30, 2011 at 10:14am

I think the orbiting is a combination of the Compass declination being slightly off and the latency of the GPS amplifying the issue. 


Comment by Rob_Lefebvre on October 30, 2011 at 3:09pm

Could be that, but I'm sure the control interaction is playing a role.  Fact is, when you give forward cyclic, the heli also moves to the left (or is it right...?)


Anyway, looking pretty decent, though I won't be standing that close with my 600. ;)

Comment by Pbreed on October 31, 2011 at 10:30am

To get my Trex 600 to loiter well I needed to add a term that uses GPS velocity.

(Basically D term on position)

This was not arducopter code it was my own code  It hovered better than I could and rapidly responded to wind gusts etc... With the good 20Hz GPS it looked like It was sitting on an invisble step ladder.




Comment by Randy on October 31, 2011 at 4:30pm

We have a rate controller nested in a position controller so I would have thought that if the speed got too high it would slow it down.  Perhaps we (i) should add some logging of the PID values to try and make it easier to diagnose the problem.

In a separate discusion Olivier suggeted either dynamic PID values or a feedforward setup so that might be worth a try as well.

Comment by Jason Short on October 31, 2011 at 4:36pm

I'm testing a new alt hold patch that's better than the current one. I'll fly tonight and push it to GIT. Let me know if you see an improvement.  


Comment by Jason Short on October 31, 2011 at 5:57pm

OMG, just got back from testing alt hold with a new approach to the barometer sensor. WoW, i've never seen such a good hold and no oscillations at all. The baro drift of a meter or so is still there but it's not bad. Will post a vid soon.


Comment by Randy on October 31, 2011 at 7:00pm

fantastic, can't wait to give it a try when i'm back in tokyo this weekend!

I guess i'll have a look through the code to see what you a high level, is it more filtering?



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