Got a new HMC5883L external magnetometer (non-3DR) and installed it with the chip at exactly the same orientation as the onboard one (on APM2.5) about 15cm above the copter frame, redid my compass calibration and compassmot (got 1% interference!), went for a test flight and my quad still “toiletbowls” badly, I’m hugely disappointed, HOW can that be, I thought an external mag removes the cause of “toiletbowling”!
Then I had a look and tried to find out if the rotation orientation needed to be changed but there’s not much information that I can find for using non-3DR magnetometers.
My compass does point north when the frame points north so why the toiletbowling?
Since your compass is pointing North when the MP is indicating 0 (360) degrees, then the only thing that might be wrong is that your compass is upside down in relation to the APM compass is all that I can think of and is probably not the case.
It is odd but I double checked, the numbers on the mag chips are both facing up and the ‘dot’ on the chip is pointing the same way on both the ext and onboard mag. I have just done a complete reset of the board back to defaults and will try again tomorrow when it’s light. Very frustrating, have been waiting for 5 weeks for this mag to arrive and the copter Loitered better (not great) with the onboard mag.