I narrowly avoided a flyaway with my newly finished Flame Wheel 550 with an APM2.5. From what I've determined so far, the issue seems to be related to mounting the APM between the top and bottom plate on the FW550 I had it mounted directly on the bottom plate that is also a PCB with the power distribution traces in it. I think this confused the compass chip in flight.
I had left the APM in the "learn mag offsets" mode and evidently it got very confused. After my close call flying waypoints, using MP, I looked at the mag offset settings and found the Z mag offset setting to be way outside of what was acceptable. It was about -560.
I also tried to set the mag offsets with the manual calibration by flipping the copter every which way, etc.... This seemed to work, but I got a message in MP saying that the calibration failed after I did it.
It seems clear that the APM needs to be mounted up high away from any metal and magnetic fields caused by current flow through the power distribution board. Either that, or adding an external mag.
For those with more experience with the APM 2.5 and mag issues, does this sound like a good diagnosis?
Thanks in advance.