Compass Heading Perfect N/S, but off 20deg E/W

We’ve got a 3DR external compass/GPS for the Pixhawk mounted about 3/4 down the boom on the heli. After maybe 10 Live Compass Cals using every technique we can think of, we are getting correct headings when we point north or south, but facing east or west, we have about a 20 degree error. We are using auto declination and our offsets seem very good.

Any ideas why only E/W headings are off?

We get a slight toilet bowl in loiter because of it.


What do the offsets look like?

This is maybe a bit outside of my knowledge. I do often check the North alignment, but it’s been a long time since I checked East/West rigorously. So I’m not sure if what you are seeing is normal.

How exactly is the mag mounted to the boom? Is there any steel anywhere near it? I always mount the mag using aluminum, carbon-fiber, G10 or plastic mounts, and non-magnetic stainless steel, aluminum or nylon screws. You also need to consider if the tail rudder pushrod is causing the problem. If it is, the only thing you could do is a carbon fiber pushrod.

How bad is the toilet bowling? It is normal on a heli to TBE a little bit if you just yawed it quickly. This is because of the way the tail rotor shoves it when you yaw.