Compass Calibration Issues

I have a Pixhawk purchased from a diydrones member on a 3DR 2014 Quad frame. So far I have not been able to get rid of the prearm compass checks. I have calibrated multiple times with subpar results on compass 1 which I believe to be the external compass attached to the M8N GPS unit from eBay. After calibration and restart I get Pre-Arm Compass Offsets too high.

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These are the results from APM Planner, I’ve done it in Mission Planner and it was no better. Should I just disable compass 1 or if it is indeed the external compass try another unit?

Thanks for the help.

When there are two compasses the external compass is the first compass and the internal becomes the second compass. It looks like your external compass has an issue.

This can be verified by disconnecting the external compass/unit and doing the calibration again and seeing what the offsets are and id.

Large offsets are an indication of magnetic interference.


Yup, I totally agree with iseries’s comments.
Those external compass offsets are very bad. Maybe there’s some metal very near the compass (metal screws used to attach the compass to the frame?) I wouldn’t fly with that.

Ok thanks for the suggestion, disabling the compass on the GPS resulted in me getting a decent reading.

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I’ll have to investigate the screws and if the mast is causing problems.

I was looking at a compass app on the iPhone and it does not match up with nose direction of the pixhawk. Is that cause for alarm?

How far off is it? If it’s off by less than 20degrees then I wouldn’t worry to much. If it’s off by 90 degrees then I’d worry. As for the grey area between 20 degrees and 90 degrees… I’d probably bring them both outside away from any possible source of interference and check again.

I wonder if the iPhone’s compass can really be trusted all that much… I googled it a bit and it’s not clear whether it’s accurate or not.

I wouldn’t trust an Iphone to make a phone call let alone point me north lol.

I’ve used a regular compass and an android app and they both agree with the direction the quad is pointing within one or two degrees.

Blakfuzhun: Those compass offsets you posted for the external compass are extreme. I get numbers like that when the internal mag is mounted about 1cm from a large Helicopter motor, as often happens on helicopters. I can’t imagine you’re getting numbers like that just from metal screws. Have a look around, but I suspect that mag is just simply defective.