Bounce oscillations in PosHold/RTL modes


I experienced a weird bug today, a non-windy day. I took-off normally in Stabilize mode, then as I often do I tested the GPS-dependant flight modes (RTL by Radio FS, then PosHold, then RTL). But in PosHold/RTL modes (all GPS modes I have), once the copter was nearly stable (near the desired position), it started to bounce (oscillate) mainly on the pitch axis. Each time I changed the position with the stick, the bounce stopped until the copter was again in a nearly stable position, then the bounce oscillation occurred again. This behaviour did strictly not happen in AltHold nor Stabilize modes. Then I landed and started the on-board video recording, the beginning can be found there. I take off in Stabilize, then toggles PosHold. When I replace the copter, it stops oscillating and it oscillates again once the copter is nearly stable. At the end I switched again to stabilize mode. In RTL mode, it oscillates like this all the time, but the flight path to home is okay.
First I thought it could be linked to a tuning parameter, but I rebooted my quad just after that and all GPS modes were working perfectly again ! :open_mouth:
I don’t want my logfile to be public, but I can link it in a private message. From what it have seen all seems OK : GPS HDOP, BARO ALT, RCIN, no ERR msg … Here is the roll/pitch graph of the bouncing behaviour :

Does someone have an idea ?


My config :

  • dji F450 frame
  • 3DR Pixhawk with AC V3.2.1, fixed on the frame with foam tab (vibration levels are slow)
  • 3DR uBlox Lea-6H GPS + Compass
  • 3DR Power module (the one that comes with the Pixhawk card)
  • T-Motor MS2216 kv1100
  • 4S LiPo 3.7 AH
  • Graupner 9"x5" propellers
  • HobbyKing F-30A ESC flashed SimonK
  • as my quad is slightly overpowered, autotune fail or give very low values so I did all PID settings manually. It is a bit aggressive, without oscillations.