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Magnetometer has me scratching my head...

Posted by Steve Smetters on November 4, 2011 at 3:56pm

I have been trying to figure out why my loiter mode is circling and just plain bad compared to earlier versions of the software (I am running 2.0.49). I have been looking at the magnetometer and am seeing the following behavior (I live in Columbus, OH so have been setting the declination to -6.77).

When the quad points North the APM shows the direction as North.

When pointing South.. APM shows South.

    BUT...

When pointing East, the APM is reporting -15deg less than it should be. It should show about 90 deg and is showing 75deg.

 

When pointing West, APM is showing +15deg more than it should be. It should show 270 and is showing 285deg.

 

The following output is shown from the "compass" output in CLI:

 

Compass

-------------------------------------------------------------

enabled

Mag Dec: -6.7700

Mag offsets: -77.8462, -15.9017, 89.9628

 

Can someone offer some insight as to why I am getting these weird readings and if this is normal?

 

Thanks...

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Replies

  • Tomas Soedergren November 5, 2011 at 1:58pm

    I agree those compass readings seems troublesome. But it does not explain why the loiter mode worked better in previous FW versions.

    I too am struggling with tuning the loiter out of circling tendencies, but since I am fresh on Arducopter I cannot compare to previous FW versions.

    I will follow this thread with interest.

  • AVS November 5, 2011 at 6:24am

    Yep I found the same. Even the xbee wires need to be as far away from compass and oil pan as possible. Otherwise I found that many sensor readings become unstable. This probably seems obvious to many with more experience than myself but when I saw it for my own eyes it really hit home.

  • Developer
    Olivier ADLER November 5, 2011 at 2:55am

     

    This is certainly because you have magnetic influences on the frame. Can be caused by near wires, ferromagnetic parts.

     

    Near wires can cause dynamic changes, according to the current flowing in them. Lock your frame on the ground and try to push throttle and roll/pitch/yaw sticks. You shouldn't see compass deviation inside Mission Planner. If you see deviations, then your wiring must be redesigned or the compass moved far from power wiring.

     

  • Developer
    Randy November 4, 2011 at 9:51pm

    I wonder if it could be the enviroment where you're testing it.  For example if there were something pulling the compass "needle" north you'd see the behaviour you've described.

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