MikeDKelly's report on DCM Active and Bad AHRS

ArduPlane Plane 4.6
1

This discussion was originally started on the 4.6 issues list but it is better that we do support here in the forums.

@mikedkelly reports

When I arm my plane the status changes to DCM Active and it throws continual Bad AHRS errors. As soon as I disarm it changes back to EKF3 Active.

@rfriedman suggests

Can you set LOG_DISARMED to 1 and get logs of it? Have you tried to reproduce on 4.5?

@mikedkelly replies

Here is the log and my params. I confirmed this happens on 4.5 and 4.6 beta 4. I guess I didn’t notice it before.
Logs can be found here

2

It looks like this is a result of disabling the compass on my GPS. Does EKF3 require a compass?

3

Hi @mikedkelly,

We’ve got a wiki page here re flying without a compass.

EKF3 on copters normally requires a compass but I’m unsure about Plane. Plane is a “fly forward” vehicle which means that the direction of movement is generally the same as its heading so the requirement for a compass is less. I’m afraid that I don’t know the details though.

4

Thank you for that. Here is the note on that page:

On Plane, without compass, after arming the vehicle will fall back to DCM (“DCM Active” message over MAVLinK) from EKF3 since it has no yaw sensor yet. This will be flagged in MP HUD as “Unhealthy AHRS” or on RC telemetry systems (like CRSF) with a “AHRS Bad” message. Ignore this, once the plane starts moving EKF3 will obtain yaw information and align, and operation will switch back to it (“EKF3 active”).

2 Likes