Magnetometer and magnetic interference

Posted by Jon-Paul on January 23, 2014 at 8:35am

Hi,

I have had my rover implementation and it's 3DR Ublox LEA-6H GPS/compass working great for the last few months.

Recently I installed two AEG airsoft guns (I know, I know, boys and their toys!), and now the magnetomer is wildly affected by the AEG motors.  Swinging the guns around on their pan/tilt mount clearly indicates an adverse effect.  Even when the AEG guns are disconnected from power the magnets in the motors affect the compass, as tested by swinging the unpowered gun/pan/tilt mechanism around by hand and monitoring the compass reading.

Originally the GPS/compass was mounted in the middle of the rover top plate, and was working perfectly (i.e. not affected by the dual H bridge motor driver mounted bottom plate at front).  In order to try combatting the AEG motor magentic field I moved the GPS/compass to the back of the rover top plate (see pic).  I still have issues despite an 18cm separation between GPS/compass and guns.

I really don't know if there is much I can do, I have no space left to play with.  I tested with a second standalone compass and this too is affected by the (unpowered) gun motors.  I know this must be a relatively common problem, I wonder how you guys perhaps with brushless motors in your rovers deal with this.

Any advice appreciated.

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Replies

  • joermyer February 21, 2014 at 3:44am

    Did you check out for some online solutions for this problem? Check out some of the airborne applications of magnetometer gradiometer. Problem might be due to some magnetic interface, thanks.

  • Admin
    Thomas J Coyle III February 11, 2014 at 4:46pm

    @Jon-Paul,

    I found that mounting the 3DR GPS/Compass on the Thumper chassis over the front motors lead to wild compass offsets when the chassis was driven at full throttle. I found the compass to be off by 40 - 50 degrees from the actual magnetic heading.

    I found that raising the GPS/Compass module up on a 2.5" high pedestal cut the offset to an acceptable 2 - 3 degrees at full throttle.

    Regards,

    TCIII ArduRover2 Developer

    • Jon-Paul > Thomas J Coyle III February 11, 2014 at 10:54pm

      Hi Thomas,

      Good to know, thanks for the update.

      My Compass was working perfectly mounted centre chassis on top plate.  That is, until I installed the AEG airsoft guns!

      Those guns have extremely dirty motors with a ton of magentic interference (powered on or off).  I even moved guns as far forward as possible and compass as far back as possible, still with shocking interference.

      For my current needs I will do without compass.

      Very interested in folks who are running APM on rovers with large brushless motors - I imagine those motors are cleaner and better shielded?

    • Admin
      Thomas J Coyle III > Jon-Paul February 21, 2014 at 5:44am

      @Jon-Paul,

      I have a 4WD Traxxas E-Maxx with a large brushless NEU motor mounted mid-chassis. I mounted the GPS/Compass as far forward as I can mount it in relation to the chassis front bumper. The compass offset values are reasonable, but it will be interesting to run the motor to see how much the compass deviates during vehicle operation.

      This is why I have always chosen 2WD chassis which allow me to get the compass as far from the motor as possible:-)

      Regards,

      TCIII ArduRover2 Developer

  • Admin
    Thomas J Coyle III January 23, 2014 at 9:42am

    @Jon-Paul,

    You might want to consider the new Honeywell HMC5983 compass which can be bought off of eBay. I have one interfaced to my PX4 and it works well.

    Regards,

    TCIII ArduRover2 Developer

This reply was deleted.