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ArduPilot 2.6 External Compass

Posted by Clive Moverley on February 14, 2014 at 6:22am

Hi there

I've just got my ArduPilotMega 2.6. I am hoping to build a RC plane that will always be in line of sight so I thought I didn't need a compass. However, I do want to record my flights so I have bought an external GPS (MediaTek MT3329 GPS 10Hz v2 (without compass)). I have just connected the GPS and APM to the computer and it acquired my location. On the artifical horizon it did have a compass that moved when I moved the APM, how does this happen when it doesn't have an onboard compass?

I also read on the paper instructions that came with the APM that the 2.6 version requires an external compass. Is this true? I didn't think it was a mandatory component. The APM should still work without one shouldn't it?

Any help and explanation would be much appreciated.

Many thanks

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Replies

  • Tommy Larsen February 17, 2014 at 11:05am

    I also have some strange behavior. I use external compass at my gps module from 3DR. and after calibration it doesn't move the copter at the map when i turn the gps/compass module alone. But if i turn the APM, then it turns around at the map! When i callibrated the compass, i had it in my hand while the apm and copter stood still at my desk. The calibration went very well.

  • Lucas February 14, 2014 at 11:52am

    If you don't plug any compass to the APM this one will set the north where you card is pointing at the initialisation (when you plug it to your computer) then you have to enable the compass in the parameters and it will use the GPS for the heading...

    • Clive Moverley > Lucas February 17, 2014 at 8:28am

      Many thanks! I'll just get the plane to point north when I power it up and it should work reasonably well without one. In Mission Planner how do I enable the compass if I'm not using and then set the GPS as the heading? Or does it do this automatically?

      Thanks for the help!

      • Lucas > Clive Moverley February 17, 2014 at 8:50am
        You have to go on the parameters list and check around compass properties there is one that allow you that, you should do that before flying. Check on ebay but you can get an external compass for only few $ and it's highly recommended if your using the APM in fail safe or auto mode...
  • iskess February 14, 2014 at 10:25am
    Are you planning on auto missions? I have found auto missions to be very inaccurate and unpredictable without a compass. Auto takeoff and auto landing require a compass. If you just want to use FBW and be able to RTL in an emergency, then you don't really need one. You can find stand alone compasses so cheap ~$15, why not have one.

    I don't know how the 2.6 knows your heading on the bench without forward motion and no magnometer. I'm guessing it is using accelerometers to detect lateral movement and converting that into a heading change while using GPS track data. If it stats accurate on the bench, then I'm at a loss.
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