What exactly causes the "Alt Disparity" error?

Hi guys

Unfortunately I have a few problems with my Pixhawk. I use the Pixhawk with the 3DR uBlox GPS + Compass module. Sometimes I get the message, that a compass calibration is needed. But I did the calibration during the first setup. It seems that Pixhawk looses the compass values.... This is very strange... Another problem is the "Alt Disparity" error that shows up sometimes. Can somebody explain what  this error causes? I have never got those errors on APM 2.6...

Many thanks in advance


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  • I see several people reporting they have this error, and that it relates to ekf (which as a newbie I don't yet understand), but have not seem anyone report a fix.  I am experiencing the same error also on my just out-of-box 3DR X8+.  I have it connected to a MacBook Pro, and running APM Planner 2.0, which I was able to get working after applying the 8-18-18 day build of the installer.  The release version available to download for Mac from the Ardupilot,org website crashes during install while attempting to install old version of library but requires newer version.


    (says it is expecting version 5.9)

    That's where I found the day build

    Is there a version of the installer that addresses this issue on Mac?

    The one suggestion I have seen that I dont know how to implement but could explain it is:

    increase Alt Disparity pre-arm check threshold to 2m (was 1m)

  • I still have this alt disparity error on 3.2rc10, with ekf enabled.

    What does it mean exactly? If I disable prearm check it flies well.

  • I was actually wondering the same thing?  I was getting it as well.  let me know when you find out :)

  • Ok now I am getting this Alt Disparity error also and hoping someone has a good way of fixing this error.

  • In the same boat with VR microbrain. Afcours we are running release candidate versions. Have you tried gooing back to the relaese version in mission planner?

  • doing a quick google after replying, it seems to be ekf related, which would explain why these two flight controllers suffer and not apm, i believe apm doesn't have enough power for ekf.

  • I've just seen this too setting my new VR microbrain too,

    so would also like to know.


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