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CompassMot of 123%, but I have good separation... Help

Posted by Pedals2Paddles on April 1, 2014 at 3:44pm

I just ran the compass mot test for the first time.  I was expecting a low percentage, but instead I got 103% to 123%.

I have the external GPS/Compass mounted well above all the primary power.  In the attached photo, the power distribution board and ESCs are located between the quad frame top plate and the bottom cd "deck".  The APM is on the bottom deck with zeal gel pads.  And the GPS/Compass is on the top deck.  The GPS/compass module has a vertical separation from the power distribution board and ESCs of about 2 inches.  If the answer is that it needs to be higher, that is problematic.  Right now I can put the HAL dome on it and that keeps all components inside and protected.  I could land upside down and nothing would get touched.  Not that I try to land upside down.

2014-04-01 18.25.43.jpg

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Replies

  • Pedals2Paddles May 26, 2014 at 8:44am

    The ESCs were moved lower and I raised the compass/GPS module.  Both of those things got it to 19%.  Flew great.  It is in a heap of rubble now due to a prop failure at 160ft...

    • Dave > Pedals2Paddles May 26, 2014 at 1:25pm
      At least you got it working

      LOL
  • James Overington May 25, 2014 at 11:11pm
    The heavy wires visible on top of the main frame - can you re-route these underneath? If there is any spare length, twist these wires together as this will help cause the mag field from the +ve/-ve wires cancel out. Is your mag as far as possible from any metal (ie screws). I had a vast improvement when I replaced the metal screws in my gps/mag standoff with plastic screws.
    • Simon Gibson-Poole > James Overington May 25, 2014 at 11:45pm

      As James said, remove the metal screws that hold the GPS unit together (stick it together with superglue instead).

      I had big problems with my compass calibration as I magnetised the screws by mistake when I took the GPS unit apart to have a look inside it.  Once the screws were removed, the calibration and MOT were fine (well below 30%).

  • Pedals2Paddles April 2, 2014 at 2:47pm

    Update: You're both right. The CD was definitely amplifying the effect.  At the same height without the CD, it was much less, but still too high.  So I removed the CD and placed the GPS/Compass on top of the dome.  I don't like having it outside, but I have no choice for now.

    On the CD at that height: 123%

    On a piece of cardboard at that same height: 67%

    On top of the dome, up about 1.5" higher, 23%

    • Pedals2Paddles > Pedals2Paddles April 28, 2014 at 10:03am

      I relocated the ESCs a bit lower in the frame and cleaned up the wiring in general.  CompassMot is now down to 19% at full throttle, about 90 amps.

      • Donald Wallace > Pedals2Paddles May 25, 2014 at 9:49pm

        And at 19% how well did it work?

  • Pedals2Paddles April 2, 2014 at 6:16am

    I will try both later this evening. I'm hoping the height is fine and the CD is the problem. I'll use something else instead of the CD, and that will let me keep all the avionics inside the dome.  If height is a problem, I will have to put the GPS/Compass on top of the dome, which sucks for a number of reasons.

  • Dave April 1, 2014 at 4:48pm
    Take the gps off the cd and try the test again. Maybe the cd is working like an antenna. It has a foil layer in it.
  • Developer
    Michael Oborne April 1, 2014 at 4:09pm

    if you can raise your gps and mag higher from the frame.

This reply was deleted.

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