How I got from 148% to 43% on compassmot

Ok, so I've not been that impressed with the whole compassmot thing, given it ruined a perfectly good quad. I did the whole compassmot thing, and eventually got 148%. It flew and loiters ok (eventually) but one pack to the next the toilet bowl kept coming back, and I had yaw issues and loiter took ages to stabilise.

So, I admitted defeat, and vowed to resort back to 2.9.1.

Or I did, if I wasn't so stubborn. Never one to admit defeat gracefully, I decided to give the compassmot one last chance, after a few mods.

Here are my mods to my quad (QUAD heavy from

My setup:


1. Mumetal on the underside of the APM board, in a single 8x8cm sheet. This overhangs the board slightly, but that's intentional - I wanted some screw tops covered by it.3689534433?profile=original

2. Ferrite rings on the 4 servo leads from the ESC's, wrapped twice each.


3. Errr....that's it. And I refuse to do more! I want to fly, not be constantly tweaking!

Result? With no other mods, Compassmot has dropped from 148% to 43%, and I did the compassmot to 100%, not the 50% suggested in the instructions. Once I've got the kids down later tonight, I'll re-run live compass calibration then have a test flight. Hopefully it will be the last damned time I have to do this, and I can actually get back to flying...

If this still fails...well, I'm going back to 2.9.1

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  • i want to do this compass motor calibration test but i have a question...which is,
    can i power my apm 2.6 with the usb cable as well as the battery at the same time?
    i am not using a power module, and the jp1 jumper is plugged in the board.

  • I hope pixhawk will allow this - much more capacity one hopes. Ie run 3.0.1 until a failure criteria, then switch to 2.9.1 code automagically.

    As an update to this - I bit the bullet and bought a DJI GPS stand, raises the external GPS/compass (and some rewiring), and my compassmot is now 4%.
  • External compass just arrived im going back to 2.9.1 for now also...

    I get what the change were but it seems so lame my tri flys so much worse with the "update"

    I know it should be better if my compass had less interference but it WORKED BEFORE!!!!

    it could really use a few new lines of code:

    IF: compassmot>40%



  • Sorry to hear about your crah Euan, I know what it's like (unfortunately)
    I was considering upgrading to 3.xx as well, but reading about your experiences, I've decided to hold back untill it's matured a bit more. Then again, maybe I shouldn't bother upgrading at all, as -like you- my hexa flies just fine with 2.9.1, as long as I stay faithful to a few checks before flying (check compass declination (manual), do the compass calibration dance just to be sure, and do a close to home RTL test to ensure it works properly). It flies beautifully this way, so maybe i'll stick to what I got, knowing it works. Loiter and Alt Hold (using inertial nav) as well are pretty darn good as it is now even though I have no other anti vibration material applied other than a little bubble-plastic. It may also help that my airframe is not stacked but built rather side-by-side so that I could place the PDB on one center plate and put the APM on the second center plate. ( my hex is a modified quad, with two center plates so the frame is extended)
  • I wiped them in my haste to "upgrade" to 2.9.1. Facepalms all round.

  • i don't have any ferrite and everything works fine!

  • It is just my curiosity on magnetic interference.

    Actually, compass interference is not my problem with AC3.0, no TB effect now.

    I thought that magnetic interference is the reason to uncommanded yaw issue.

    But it might not be the reason.

  • It's possible Jiro. But I can't be sure (wiping the logs when "upgrading" down to 2.9.1 doesn't help).

    However, I need to remain open to suggestion, that it might not be mag related. Afterall, I had a bizzare situation where the quad refused to arm (unless it was via MP) once. I had just completed a loiter / flight test (that "failed", naturally), landed ok on Stabilise without incident. But when I went to take off again...nothing. When I armed manually via MP, it flew as if nothing had happened (loiter and auto flights excluded of course). A full power on/off fixed it later, but again, this sort of thing didn't happen in 2.9.1 on an unchanged airframe.

    Just annother 3.0.x "feature" - failsafes that kick in for no reason, and without any notice or alert which one has just been activated. Would be good to which failsafe was running via mavlink maybe?

    So my problems with 3.0.x aren't just due to compassmot (though this is the main problem). So yes, I'll be waiting until we're a good few releases into 3.x.x until I try again. But I may try the new 2.6 external compass from 3DR, which is supposedly due out tomorrow.

  • Euan, sorry about your crash.
    You said that switching from alt hold to stabilize involved fall out the sky with no power.
    What do you think about magnetic field difference?

    Anyway, recent stability patch for AC3 is not good for stability other than loiter.
    So, I agree with your thought that wait for the next release.

  • The props are on upside down.
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