Ahrs and compass instability

I am using Pixhawk and GPS in a 4 channel foamy.
Firmware 3.8.4 and MP 1.3.56 with 433. mhz 3DR link
Installation and all calibrations done with good results.
All looking perfect and I get the green LED on Pixhawk

Looks ready to fly but after a while (15-30 minutes) the ahrs and external compass start drifting all over the place and MP reports bad ahrs and compass.
GPS remains stable and everything else seems to work in manual mode.

Not fit for flying at all.
New charged battery no difference.

Disconnect/re-connect the battery returns everthing back to normal for a while.

Any ideas ?
I would guess hardware.


Disable the compass, for plane the GPS heading is enough

The bad Ahrs message compare in MissionPlanner HUD at boot while the gps satellites are missing .

Hi lucamax, do you recommend to always disable compass on arduplane? It won’t affect flying with crosswind, for example? Have you tested this? If this is not mandatory to use it, why it’s not on arduplane documentation?

Thanks in advance!

Generally for plane I would say that if your compass works well and do not give you problems, keep it .
If you have an external compass use that one and disable the internal one.

If your compass shows errors frequently and your gps works fine you can calibrate your compass but disable it with COMPASS_USEx parameter set to “0” .