I have tried to use the APM 2.5 on the FPV Raptor without great success.

First of all, it does not keep altitude during turns in Auto and secondly, it only uses throttle to try to keep altitude. Have a look at this:

https://www.youtube.com/watch?v=_ygBPhJt6Wk

Anyone has any idea how to teach the APM 2.5 to use the elevator instead of just throttle to get altitude?

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Can you post your dataflash log. I would guess that you roll rate and pitch rate are too low, or you haven't configured level correctly? what version of AP are you using?

Dear Bill,

I am using APM 2.5 and FW 2.74b. Manual, Stab and FBWA are fine. Haven't tested other modes yet.

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Hi Anthony! It looks that your pitch PID is not very tuned, as you I've seen most default parameters on your log(that are an excellent starting point by the way). 

I recomend you to follow the tutorials here: http://plane.ardupilot.com/wiki/flying/tuning/ and specifically this one here: http://plane.ardupilot.com/wiki/roll-pitch-controller-tuning/ if you haven't done it yet.

Hope it helps!

I still have a lot to learn about the APM and every information is welcome. Thanks for the inputs. I have looked at the graphs, showing the output to the elevator servo in relation with the flightmode, speed and throttle and there is hardly any movement. It seems the APM only want to correct the altitude by throttle, not using elevator.

Is it enough to do the simple level in MP where it only asks you to place your plane on a level surface or should one really do the more complete level test ( i presume it tries all 3 axis) ?

It will when you get the tuning set right.

Giving up is not in my dictionary:

http://www.youtube.com/watch?v=qyXQVW6FXh0

My first clue was that I should maybe give some uptrim to begin with. The downforce of the motor may be just too much and the plane should have a slight tendency to go up instead of level. So I started with 50% throttle in stabilized mode and gave it uptrim to a very, very slow climb.

Secondly, I changed these parameters to the following values:

PTCH2SRV_D--------0.02
PTCH2SRV_P--------0.6
KFF_THR2PTCH-----0.5

 Which gives the PID settings as in the picture. Seems all these changes solved the problem. But there remains still 1 question: why does the APM steer the plane in a dive where all that needs to be done is up elevator. The logic of the FW should be to prevent it from flying below the programmed altitude. Just a bit of elevator up should do...... ?????

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