Greetings... a bit long, but please read on :
Hexa, APM 2.5, 2.8.1 A few weeks of trouble free flying. Then while in stab/simple mode, bearing suddenly starts to drift about 60 degrees, but only when I yaw left or right. When the nose is in the GPS locked take off direction (pardon my terminology) it holds true. As soon as the nose is turned left or right, it gradually starts to shift bearing in that direction, (as if it is shifting to just stable mode). It was suggested that I check for wiring interference. Everything good as far as I can see, but problem persisted.
Then it was suggested I upgrade to 2.9.1, so I did. With all the required things done for 2.9.1, including foam under the APM, checked PIDs, everything calibrated... I also insured again that all the wires inside were neat & tidy, and took it for a test flight. Again, stable until I turned the nose left about 90 degrees - the bearing drifted in that direction. So when I tried to move forward, it would pitch to the left about 60 degrees. When I tried to bring it back to me, it pitched right about 60 degrees. It was flyable, but I had to adjust. I landed, back on the bench.
The next day, the last 2 flights: Made sure switches all good on the Tx. I take off, hover about 15ft in the air. Suddenly it starts to move to my left without me touching anything. As I try to counter it, the roll stick does less and less, 'till the stick is as far to the right as it will go! The copter just keeps pitching way off to the left... no control. It crashed, but no apparent damage. I take it in, check it all through, recalibrate everything, & try again. This time, I hover it right in front of me at about 6 feet off the ground. Stable for 30 seconds, then it starts to move off to the right. I took my hand off the controls for a second, and it takes off towards 3 o'clock, pitched right over. Controls maxed out to counter it, I had no control. Crashed again.
It's on the bench. Logs attached, 3 more to follow. (no wireless telem, USB to APM).
Any thoughts? Thanks...