Recently I obtained an apm 2.5 and I have an error on my mission planner that I can't figured out yet.  The error is Bad compass health and the error won't let me arm. I did all the procedures for the compass and it didn't work out.  Can someone help me?

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So you were able to run the compass live calibration without errors? If you view the HUD in mission planner does the compass respond when you turn the APM?

You could try an external compass if you have one and if not, and you aren't performing any flight modes that require knowing the direction the device is facing, then you can turn it off the arming check in the parameters.

Yes I did the live calibration inside mi home and it come successful but I tray it outside and come out with not enough data.

And yes the HUD in mission planner respond but every time that I connect the APM to the mission planner the front is pointing on different direction. No I don't have a external compass where I can found one?

and Thank for you respond.


I have tried 2 new external compasses, located my ublox unit 5" above the 3DR hex, and performed multiple calibrations including compassmot, and still BAD COMPASS HEALTH. I have gotten 1 half way decent auto flight out of the last 10 attempts. The good news is I am getting way faster and better at stabilized flight. Any ideas appreciated.

William, the ublox external compass is available on the 3DR website.

Set your ARMING_CHECK to -9 to bypass the GPS check when arming.


Hi William,

from my experience, bad compass health disappeared once I removed all magnets and unnecessary metals off my plane. Beware of this if you have something aboard that has impact on magnetometers.. It seems they are very sensitive.. And yes I use external GPS with mag on the same board from 3DR..


I was able to solve this problem by moving the GPS/Compass.  There were no magnets, but I think the compass might have been swayed by the motors or power distribution.  I also moved the 3DR APM power supply.  I haven't had this problem with Pixhawk yet, and I have 3 of them. 

Also, if you're using APM 2.5 you have an onboard compass.  APM uses the compass built into the 2.5 board by default.  

To use an external compass you have to cut the trace on the APM board.  Otherwise I think it uses the internal compass even if you have an external connected.

Remember, on APM 2.5 the compass is built into the board.  You have to cut the trace on the board to use the external compass.  I don't think the I2C uses the external compass unless you cut the trace on the APM 2.5.  On APM 2.6, it's already cut.

I am sending the ublox back to 3dr for evaluation or replacement. It seems odd to me that 2 new APM's and 2 new GPS/ mag units would be defective. If 5" above the hex on a plastic pedestal doesn't isolate it, I am out of ideas.

Check your compassmot values. If they are NULL, change the to 0. You could be running an old firmware or mission planner which had an issue with compassmot not setting the values properly..

compassmot values set to zero, calibration done, all -150 to 150, installed third external compass, verified internal compass disabled, still, bad compass health.  i want to reso;ve this and document here to help others. 

thank to all I all ready solve this issue.

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