PID tuning --> parameter mapping (tuning difficulty for alt-hold)

ArduCopter
1

I’ve been wading through the discussions on tuning, and I still can’t find an answer to my question. First, my problem: having trouble tuning a 7" quad. I’ve got oscillations on the thrust in altitude hold mode (couple Hz maybe, easily visible to the naked eye). Stabilize mode flies well.

I’m looking for the parameters that control PID values for the altitude feedback loop. I can’t tell which values I need to change in the extended tuning screen and/or I’m not allowed to change them to what I want, and I can’t figure out where some of the numbers show up in the parameter list. The “Altitude Hold (Alt to climbrate)” is my best guess at the PID that I should change. On the Extended Tuning screen I have P value for that, but I can’t change it below 1 (it’s trying to protect me from myself). And I can’t find where that number exists in the parameter list. I don’t have any parameter in the ATC_ group that has a value of 1 or looks like it matches that setting. Also, do we not have any I or D on that feedback loop for altitude hold?

I have messed with the motor expo and the motor thrust min, that’s what finally got stabilize mode flying reasonably well. Now I’m onto alt-hold. My admittedly rudimentary grasp of these things tells me that my P gain for altitude hold is too high, and/or I need a bit of D to damp the response. Is that right? If so, where are the parameter names for those values? It’s my impression (from looking at what happens), that the autotuning does not check the altitude feedback parameters, is that correct?

Also, my version of MP (1.3.74) has, on the extended tuning screen, differs somewhat from the screen captures present in the documentation. I have a “P” for Throttle Rate, but no “D”. The documentation at
https://ardupilot.org/copter/docs/tuning.html
has a D as well. much thanks, Matt

2

Please do tell us if you are using ArduCopter 4.0.6 and if you have read https://ardupilot.org/copter/docs/tuning-process-instructions.html

3

Arducopter 4.1.0-dev and I have read those instructions MANY times. However, apparently I’ve been chasing my tail so much I missed something—I just re-read it again and I see the PSC_ parameter settings referenced in there, and I see now that those are the parameters that govern the PID values I was asking about, notably PSC_POSZ_P. So now I have some more settings to play with, thank you for re-pointing me towards that reference.

4

Also I have confirmed that “AltHold kP” in the real-time tuning knob list controls that PSC_POSZ_P parameter, so I’m going to go out and see if varying that improves things. I will report back.