External Compass direction

Hi pilots,

If you look at the picture you see how I have mounted the external compass and GPS. The arrow the the direction it should be mounted. However I have not followed the direction because the wires come out of the left side of the module.

Ofcourse the compass direction is wrong now. If I point the nose north the direction it gives is not north.

How can I change this? By the way the APM itself is upside down so I have set AHRS_ORIENTATION to 8. The APM itself is pointing the correct way. The artificial horizon is correct.

So, I should correct the magnetometer readings. But how?


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  • For some reason I can't get it to work. I may have found an explanation. When I turn the APM 2.6 itself the compass turns from south to north or whatever I point it to. So it seems the APM has an on board compass.

    I assume it would cause problems when there is an on board compass AND an external compass in the GPS module. Am I correct on this? If so I have to do this: http://copter.ardupilot.com/wiki/common-external-magnetometer-for-i...

    OR does the north, south, west indicator on the OSD also move according to the gyro sensors in the APM board and not only based on the compass?

    Last thing, can I fly auto missions with a crooked compass?

    Thanks and kind regards

  • It is very strange. No matter what yaw I set it to it still keeps pointing in the wrong direction. I give the APM a power cycle after I set the yaw of the compass.

    • Admin


      You also have to remember that the compass is on the bottom of the GPS/Compass module so it is upside down. So not only do you have to change the yaw direction, as you have done, you must indicate that the compass is upside down.


      TCIII AVD 

  • Developer


    There are some instructions here on the copter wiki which show how to figure out what the orientation should be.

    • Thanks Randy for the link. Honestly I had already seen that. For some reason none of the orientations works good enough.

      The direction is correct i.e. move the plane left, the compass goes left and vice versa. But when I point the nose of the plane north it does not point north. It looks as though I cannot be compensated enough. It looks as if 270 degrees is not enough compensation.

      I hope this post make any sense.

      Kind regards

      • Moderator

        Reboot and redo compass calibration after changing compass orientation. Also check your declination is correct for your location.

        A small variation in direction is OK, ie 5-10°.

        • For some reason I thought this was a live adjustment. I was wrong.

          When I am able to work on my plane again I will check this. This should fix it I think.

          By the way, +90 degrees yaw should do the trick? I will check this out.

          Thanks for your kind help.

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