Takeoff mode has a bug? Copter oscillates up and down or stays on the ground

[mm1]

Hi, I’m having trouble with takeoff mode. While PX4 is in takeoff mode, the aircraft either

• lifts off then oscillates up and down never reaching its takeoff altitude.
• stays on the ground with the throttle at an intermediate level. The thrust is just barely enough to not lift off the ground. It’s actually pretty concerning.

I have three log files showing problems while in takeoff mode:

1. this shows oscillation: Flight Review
2. this shows the aircraft stuck on the ground with intermediate throttle: Flight Review
3. this shows more oscillation: Flight Review

This problem seems inconsistent. It happened today. But we’ve also seen takeoff mode work as expected on other days.

[Jane]

This is really curious behavior. It seems like the drone just doesn’t get enough thrust to takeoff or to maintain its preliminary takeoff. However, the same drone consistently took off perfectly in QGroundControl’s mission mode. Compare the above logs to these two:

• The same drone shown above by mm1 (we are on the same project) took off perfectly in this case (same code): https://logs.px4.io/plot_app?log=21ecd86d-4b86-4266-8e3e-66d3029f4be5

• and also took off perfectly in QGroundControl (consistently)
  e.g., https://logs.px4.io/plot_app?log=6342cc34-1771-4cc0-92bc-e3bb1905a130

That is why we are wondering if anyone has any insights into why px4 takeoff mode seems unreliable?

[sibujacob]

Are you using a Hexacopter ?

[Christian-Born]

Hey there, I encountered the exact same problem with a recent flash from master in combination with QGC daily.
Try using both in stable that fixed it for me.
Cheers.

[bresch]

@mm1 Please reduce the gains on the yaw rate controller, this is likely to produce severe issues