Just to keep all my questions in one thread ...
I've had a productive session of PID tuning in my garden
My values are now:
Tilt Rate D: 10000
Tilt Angle P: 65
Tilt Angle I: 0.0025
Tilt Angle D: 5500
All the rest are at their default values.
Here is a quick video of my last test flight where everything seemed pretty smooth:
However as you'll notice around the 27 second mark, you can hear the motors starting to make a *zingzingzingzingzing* sound, and this seems to correspond to the sudden increase in accelerometer vibration in the attached log file. It also corresponded with the X8 starting to feel soggy on the controls and starting to drift around more.
My question is ... which came first, the chicken or the ....
... the sudden high vibration which upset the attitude estimation and caused the motors to start oscillating, OR something causing the motors to start oscillating which was then picked up by the accelerometers?
I noticed this several times during my test flights – at first it would be very smooth, but then after a short period of hovering it would start this zinging routine. It was dead calm this evening, apart from the turbulence in the garden I guess. But even hovering in ground effect couldn't stimulate this zinging, at least not in the first parts of any flight.
The zinging is evidently the motors spinning up too much, the power being cut too much, then spinning up too much etc. Would that be caused by P being too high? Or does the frequency of the oscillation (several Hz) point to D being too high?
I still don't know what is a 'good' value for Tilt Rate D ... might that be adversely affecting things?
I've also noticed that my MOT_YAW still has an offset, despite the 80 top /100 bottom mixing table I'm using which seemed to eliminate the offset on the bench. Maybe this is contributing my problems, so I will try and fix that next before fiddling with anything else.
Many thanks for your help guys, I feel like I'm really making progress now. If I can just sort out this zinging, my hopes and expectations of a rock steady aerial photography platform using the AQ will start to come to fruition
Cheers, David