I was having some problems with my quadcopter (running the APM 2.5) shooting off in random directions when I put it in Loiter or RTL modes.
After doing some reading I came to the conclusion that this was probably due to interference having an effect on the built-in compass on the APM. I bought myself a nice new 3DR GPS module with the built in compass thinking everything would b resolved, but when i've tried to do the compass calibration to give me the magnetic declination offset numbers, the numbers are so crazy that that the AMP won't allow me to arm.
I've tried it several times, even went out into the middle of a field to do it, but the numbers that are returned are up in the thousands.
If disconnect the Mag lead from the APM, and select 'onboard magnometer' in the MP, and do the dance again, i can get much more sensible numbers (inside the recommended -150 to 150).
The problem with this is that my quad still shoots off at top speed in a random direction when i put it in Loiter.
Any suggestions???? I assume he new GPS with compass module is compatible with the APM 2.5?