Loiter mode - Oscillation in Pitch axis

I have non standard copter frame. It is 280 sized X8 with DYS 1806 and 5x3 props. I call it Beast X8 :slight_smile:

After autotune it is flying very well in Stabilize and reasonable well in Loiter/Poshold. Only what I had to do is lowering “D” to remove fast oscilations during start procedure (before lift off, guess that it is based on ground effect)

But in loiter I am getting kind of strange behavior. During fast stop or in reaction on wind gust copter starts oscillate on pitch axis. Copter is siting almost on one place and moving nose up and down.

Video - It is visible here (about in middle). edit : during last session I seen even bigger amplitudes as during this video I always hit stick soon when it started to get rid of it.

Log from last tuning session is here - Log .

It was long session with this progress >

  • decreased D to remove ground oscillations
  • decreased various parameters including pos hold break angle and loiter PI

result is questionable - now I getting less problems during flight because copter is breaking more lazy. So there is less fast stops and so also less oscillations. But it is still there - for example as reaction on wind gust.

Also what maybe can help - if I fly in loiter, copter don’t set angle and fly but increase angle, then decreasing it and increasing again and so… again I think that it is only in pitch axis. Similar oscilations but with lower amplitude and stretched into line.

Rest is ok (by my opinion)

  • vibrations are low , pix is mounted on omnimac mount
  • compasses should be ok
  • enough sats (BN-880)
  • board is Pixhawk Lite (no space to normal size)
  • Taranis E transmitter
  • 5800 3S lipol
  • brand new Carbon filled nylon props used during last test
  • CG was close to copter center (but probably not 100%)
  • slightly decreased Throttle params (recommended by someone as way from extremely low PID’s on those small configs)
  • alt hold is on 50% of throttle

Can somebody look on log and tell me what to set or what to fix ?

So I fixed it. I noticed that there is fast oscillations in roll axis and slow in pitch. Resolution was easy - set independent PID’s and decrease D for roll and increase D and decrease P for pitch. And done, it flies much much better (although some fine tuning will be needed)

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