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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    • I'll try tomorow.
      Today we are so sad in France

      We are Charlie
      • Hi Guys,

        I have struggled a lot with the same issue using V3.2

        S900 using PIXHAWK, Castle Creation CC BEC PRO, etc.

        I have reinstalled V3.1.5, and it seems to work now.

        Still need to do the maiden flight, but so far so good.

        Is there anything I can do for you to help you to understand?



    • That screenshot looks very familiar.  When mine failed on the AC3.3 version, I got a very similar result. (I'm not sure if it also does this on AC3.2 during a startup failure)

      I found that I can get it to boot up correctly if blow warm air (my breath) on the FC for a minute before powering it.

      • I am curious,  are you using ESC with a BEC? And are you using external LED (i2c one)? 

        • The dropix have redundant power supply: +5V from power module and +5V from Castel creation Ubec

          I don't use the external led for the moment, try it but doesn't work, i don't care, it's make 8 years that i flight multi without.

          • 8 years of flight with Multi you say....you must be very experienced pilot.

            • Yes,8 years about 800h of flight.

              Started with X-ufo silverlit with mechanical gyro ;-) (end 2006), that i'd changed for ASCTEC piezo gyro, after UAVP (first gen based on PIC) then Mikrokopter.

              In 2009, i joint French company that try to make some uav, as program manager for multi-rotor, they use Paparazzi.

              i'd designed for them about 12 different frame from nano quad to big hexa.

              I' was the pilot too, for test, demo, services.

              I'm the first "télé-pilote" according to the French aeronautical administration (DGAC)

              And now I've my own business for instruction, advice, and i develop my own omni-role multi rotor according to the French regulation, based on one of the best UAV system that I've to flown: Ardupilot ;-) that i used for about 2 years and that make me stop (among other) my collaboration with the company ;-)

              Voila! you now everything, but we are now fare aways from our issue ;-)

              i'm going to fly this afternoon, unplugged the 5V Ubec and see... there's about 30 to 60km/h of wind, i love;-)

          • can you try unplugging your backup castle ubec and see if this affects acc issue at all? In my case it did. haven't had a single acc hysteria for several days now. 

            also onboard LED heats up the board a lot an the external LED helped a bit with baro stability. 

  • Hi guys

    I seem to be having same problem. My board is Fixhawk clone. Currently "Accels not healthy" is occurring about 50% of a time. When issue is not present machine seems to be flying OK but I did only very quick test flights. From my knowledge machine was flying ok on older firmware before 3.2. Following advice in this thread I changed log_bitmask to 131070 and my findings are as follows (logs attached):

     - when it does arm both IMU show reasonable values (see good graph)

     - when it does not arm IMU1 is ok, but IMU2 accel X/Y/Z are flat lines with completely silly values (see bad graph)

    Test setup:

     - Fixhawk clone hardware

     - Arducopter 3.2 firmware

     - temp ~10deg Celsius (~50 Fahrenheit)

     - powered via power module

    Current conclusion:

    As this is professional AP machine I'm think I will be replacing faulty board. Unless advised otherwise (?).

    Further investigation:

    If developers could point what data or tests are necessary I should be able to help further. I don't have toolchain setup at the moment but I'm ex embedded software guy with access to electronics lab so I can potentially try to help with more advanced diagnostics if pointed in right direction. Just say what you need.

    Hope this helps


    Good graph:

    3701906123?profile=originalBad graph:



  • So, the mystery deepens.   My Pixhawk is suffering with this issue and I have a log uploaded on this thread showing the IMU discrepancies on XYZ axes...

    It has now got to the point where it will fail prearm checks the majority of the time with bad accel health. 

    However, whilst fiddling yesterday I worked out that when powered via USB (not lipo) it will pass pre-arm checks.  As soon as I unplug the USB plug and plug the lipo in it fails pre-arm checks.  I did this 5 times in a row with the same results?

    Any ideas? 

This reply was deleted.


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