Throttle suddenly drops to zero on 3.4-rc1 (altitude estimation issue?)

ArduCopter Copter 3.4
1

After installing 3.4-rc1 I sometimes see sudden drop in altitude, I see this at least in AltHold or Autotune modes. Today I’ve been running autotune in almost wind-free environment and on several occasions copter would quickly descend almost falling and I had to increase throttle significantly to compensate for this.

This is how it looks like in log:

Pasted image1255×597 11.4 KB

Looks like there is a problem with altitude estimation:

Pasted image1162×603 11.6 KB

Full log is here: https://1drv.ms/u/s!AklcJXM-UpFVh8UdyAdwaLywPmRpTA (can’t attach it to the post).

2

Looks very similar to my issue:

http://discuss.ardupilot.org/t/sudden-ctun-alt-altitude-change-during-takeoff-in-althold/10077

3

There is a bug in the inertial nav library that means the height output from the estimator does not have the required conversion from m to cm performed when the estimator is reporting that it doesn’t have a position estimate (ie before GPS checks pass).

https://github.com/ArduPilot/ardupilot/blob/master/libraries/AP_InertialNav/AP_InertialNav_NavEKF.cpp#L20-L23

This has been fixed along with some other updates in a PR that is pending here:

https://github.com/ArduPilot/ardupilot/pull/4455

In the meantime i would advise not flying in any modes that control throttle automatically before the GPS pre-arm check passes.

4

So if I only arm in e.g. poshold, then I’m safe, right?

5

Safe from this particular bug unless you lose GPS for longer than 5 to 10 seconds (I don’t remember the exact value) and it falls back to non-GPS mode.

6

This fix has been released with Cotper-3.4-rc2 that should appear in the mission planner’s beta firmwares link in about an hour. I’m going to close this issue, hope that’s ok!

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