Pixhawk BAD ACCEL HEALTH APM 3.2 - collecting data

A few users, myself included, appear to be having issues calibrating accels and/or arming when using APM 3.2 on a Pixhawk.  I see posts here and there, but thought it may be best if those having the issue could all 'check in' to one post so that the developers can see how widespread the issue is and gather data.

My Pixhawk will arm occasionally, and will even fly successfully.  Occasionally however it will not arm and I will receive the pre-arm error "Accels not healthy".  A few days ago I was able to arm and fly thorugh one lipo, then after landing and swapping batteries I could not arm due to this reason.  I have attached the logs from the successful flight, as well as the failed pre-arm logs, to this post.

As you can see from these images there is something amiss with IMU2.  This is a snippit from the good flight, showing values for AccX on IMU1 and IMU2:


and here are the same values on the second attempt, pre-arm.


In the 3.2 release thread a few users had mentioned the issue and Randy advised to set the log_bitmask to "131070" so that it will log everything including the pre-arm checks.  I encourage others having the issue to do the same and share the logs and experiences here so that we can find out what is going on here - is there a bad batch of Pixhawks in the wild that only now show the hardware errors due to something new in 3.2, or is there an issue in the APM software?



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                  • Developer

                    The logged temperately is from the ms5611 which is heated by surrounding electronics - it quite often shows a temperature 40C above the local air temperature.

                    For altitude calculations we use the temperature from the digital airspeed sensor if one is fitted (on fixed-wing).

                    Note that incorrect temperature only makes a small difference to altitude calculations. It is worth using a better sensor when available (like the airspeed sensor), but it won't cause a significant issue for copters that don't have an airspeed sensor.

                    Cheers, Tridge

  • Hello,

    Just to say that I have this issue too. Twice, after normal flights and landing, I can't rearm : message like "bad_health_accel".

    First I think it was an hardware pb : calibration failed on the field , but after recalibrating OK at home : flight 20 mn OK the week after.

    One more week after : flight OK of 10 mn (just start to drift a little in loiter mode), landing OK ant then accel check pre-arm message.

    I will try to set the logs for next time the problem occurs.


  • I've returned my pixhawk to the person I bought it from - turns out it was a clone.  Even had the 3dr logo on it and everything!  Turns out if the price is too good to be true, it probably is.  Fighting to get a refund now, good thing I used paypal.

    Not sure if it was 100% faulty board, or maybe in some clones since IMU2 was never really used before 3.2 is just find preexisting issues doe to stricter hardware checks.

  • ive seen bad accels on 3.2 bench testing a Virtual Robotix ubrain, it went away. Not sure why, but I wonder if its 3.2 specific rather than pixhawk.

  • I've seen that today. Can't calibrate it, tried outdoors 3 times. A little chilly.

    Also same issue, some flights are perfect, and some I can't get off the ground. I need to manually disable all pre-arm to get it in the air. During flight, it's fine.

  • I had one occurrence of not being able to arm on the filed. MissionPlanner reported "Access not healthy".
    The logs shows normal values for IMU1 and constant values for IMU2 of AccX=60.39, AccY=56,18, AccZ=56,80.

    This stayed the same upon disconnecting and reconnecting the battery.

    Trying to do accel calibration on the field failed, as reported by MssionPlanner ("calibration failed") and APMPlanner (values all "NaN")

    I don´t know if it is related, but I noticed that in the cold temperatures here in Germany the Accels drift apart quite a lot on temperature changes. Auto log-analysis gave me an IMU mismatch warning (0.71) and a fail (2.1) ...

    In the attached Better.BIN you can see the drift quite clearly if you compare des AccX,Y,Z-values before the start and after landing.


    • I had assumed it would be in "Bad.BIN" but when I view the graphs for that log I see decent accel values3702535852?profile=original

      • You are totally right.
        Too many logs on my desk. Sorry, I obviously confused them.

        34.BIN is a faulty one...


        • WOW that looks very similar to my issue. I'm wondering if temperature change really is the issue.  I'm in the US on the east coast (WV to be exact) and it's rather chilly outside this time of year.

          Still, I've seen similar behavior in my office, but not as often... Really wish I knew for sure before I send this unit back for replacement tomorrow - I'd hate to waste time shipping if the other unit will experience the same behavior.

          • @thatJoshGuy, I'm still having the same problem as you (can not calibrate Accel using AC3.2).  Logs say I have mismatched IMU, but I do not have any Idea as how to fix it.  As a result I have gone back to AC3.1.5 where I have no problem......Copter flies fine!

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