Unstable Alt Hold

I have been have a problem with Alt Hold / Loiter height being unstable. When switched to ALT Hold and Loiter The copter will bounce up and down very sharply. This dosn’t happen in every flight (Probably one in five). If I land and cycle power the issue is gone.

I have noticed this issue with all versions of 4.0

Cube Black
Here GPS

Enclosed are two log files
2020-01-26 16-25-15.bin is the flight where the copter bounces in Alt Hold
2020-01-26 16-27-41.bin has no issue

David Ardis

What’s the reason behind the extraordinary motor arrangement ?

I assume you mean you mean why there is no motor 1 and a motor 5.

I have an early cube which had a problem with motor 1 pin.

Its a standard quad

You may want to run through the tuning process Wiki to get all the various filters configured correctly, and specifically ones that affect altitude https://ardupilot.org/copter/docs/tuning-process-instructions.html#test-althold

This doesn’t look like an AltHold problem but a roll and pitch problem based on the two logs you sent. I would need to see the problem with fast attitude logging and PID logging turned on to help you further.

It looks like you have done a proper tune but you may benefit from implementing the harmonic notch if this is noise related.


This is the machine you and I where testing filtering on back in Sept - October last year.

Filtering is turned on but I an considering doing a complete re-tune with the filtering turned off and then setting up the filter again

David Ardis

I would suggest setting up the harmonic notch and then doing a tune with the filtering on.

Can you send me a log showing the problem with high speed logging turned on.

I can’t see any sign of alt hold oscillation you talk about but I can see signs of roll, pitch noise or oscillation but I can’t tell with the slower logging.

If you can give me a video that would help too.

Don’t worry, we will get to the bottom of this with the right data.

His CTUN.ThO is a curve, until he invokes any height-dependent flight-mode, when it becomes a see-saw.

@ardisd can you please fly a bit longer, with 3-4 switches between Stab and AltHold ?

@Leonardthall @ThePara I will do a flight with full logging and the changes in flight mode in a few days when the weather improves