Can Mission Planner detect if this compass is being used? Maybe MP’s Service Bulletin feature would be appropriate.
The compass calibration succeeds with relaxed using all 3 compasses with 3.5.4, and “inconsistent compass” only shows if you move the frame. I attempted a flight with 3.5.4. I had no warnings until liftoff and still it flew well in stabilize. When I switched to position hold, then it got fun and bounced it off the ground before a very rough landing. I also wasted 2 days disassembling and repositioning components trying to get rid of the error before I gave up and came here.
The clarify a bit, the “inconsistent compass” message shows up when two (or more) compasses are pointing in different directions (90 degrees off in 3 dimensions or 60 degrees off in the horizontal plane) or of different lengths (200 milligause which is about 30% different) so it doesn’t necessarily require moving the vehicle. Metal on the ground or perhaps in the frame could affect the field which might push it over the limit which might explain why sometimes moving it makes a difference.
https://github.com/ArduPilot/ardupilot/blob/master/libraries/AP_Compass/AP_Compass.h#L32
A service bulletin is a good idea.
I think the inconsistent compass error will appear if the internal compasses are enabled. If they’re not enabled you should see the vehicle is pointing in the wrong direction although people often may not check this.
I tested it quickly by doing an upgrade from 3.5.4 to 3.5.5 without the internal compasses enabled. No inconsistent compass message, but the heading was off. So that answers that question. If a person was flying without the ground station, he/she wouldn’t know it.
You’re right, it did show momentarily without moving. It popped up for about 3 seconds and disappeared for a descent amount of time with a white EKF. So most of the time you look at the hud, everything appears normal.