Developer

MPU6000 scaling issue

3690933314?profile=original

 

     Thanks to help from Sami Finnila and Wesley Chuen we've found an issue with the default MPU6000 accelerometer scaling in some of the recent APM2 boards shipped in the last month or so.  You can find the original discussion from Sami here.

     Internally we use "DCM" to merge the gyro and accelerometer values together to calculate attitude.  With the recent boards we are finding the accelerometer values are 2x as big as they should be which leads to an inaccurate attitude estimate.  It's apparently possible to fly with this misconfiguration but it at least makes "the leans" more common (you can recognise "the leans" by your copter requiring more and more manual roll or pitch to keep it level as you fly).

 

UPDATE (11-May-2012):

     Craig and Tridge have completed a patch to automatically detect the scaling of the accelerometer so we can compensate.

     This patched version is being called 2.5.5-Beta and is in the downloads area.  After a short testing period (maybe 24h ~ 48h), if all goes well it will be available in the mission planner.

     We're still working on the next official release 2.6 so we haven't included any improvements to flight dynamics in this patch except Adam's "Retro" loiter.  This uses the ground speed directly from the GPS instead of calculating it using lat/lon position.  You can enable this by setting the "RETRO_LOITER" parameter to "1".  BTW, it's "retro" because this is the method used in the popular 2.0.49 version of Arducopter.

 

     Feel free to post comments / issues regarding this patch release in the discussion below.

     If you have recieved an APM2 in the last month, please try the test shown above:

  • hold your APM2 flat and check the "az" value in the mission planner's Flight Data, Status screen is approximately 1000 (it should be for everyone, regardless of whether you have a new or old board)
  • hold your APM2 up-side-down (but still level) and check the "az" value again.  If it's not close to 1000 then we want your tlog!  :-)

 

     Next just roll and pitch your board a bit and attach your tlogs below.  These logs can be found in your AP Mission Planner's log directory.  On a windows machine you will likely find a recently updated file here: C:\Program Files (x86)\APM Planner\logs\YYYY-MM-DD HH-MM-SS.tlog

 

     Thanks for your help.

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Replies

  • Regarding my compass problem:

    I've got another APM2 - replaced the GPS/SD/magnetometer board,  - and it works as expected.

    So the failure is somewhere on my GPS/SD/mag board - but I verified all power & interface connections, without finding the error - the fact that SD *and* magnetometer fails on it - hints that it should be something they have in common.

    Thanks to all who tried to help.

  • When will be DMP available!!!!

    I still remember

    • When using the internal sensor fusion processor of the MPU-6000, more than half of the Atmega2560 processing capacity is free for new advanced features.

    Or I bougth something that promised what can not be delivered??

    I think  with DMP all scaling and no sense problems should be gone.

    For a board that flight absolutelly not better than a 50USD MWC I would like to have some extra features...

    Pablo

  • I found this information to update the gps and second that put more efficient. someonecan help me with this information or if I leave it as it buys?.

    http://www.multiwii.com/forum/viewtopic.php?f=6&t=1682

    MultiWii
    MultiWii project related stuffs
  • ok, thank you for the fix.

    The compass still expected to be inverted ?  - right ? - no fix there ?

  • Regards arducopter the version 2.5.5 you can install the apm 1 withoutproblems. or is it just for the amp 2. I appreciate your prompt response.

  • Developer

    I've just released ArduPlane 2.34 with the fix for this scaling problem

    Cheers, Tridge

  • I just checked and I have this same scaling issue.  Is the patched version out yet for ArduPlane?  If not can you describe specifically what the issue is and point me to the line(s) of code that deal with this?

    My rudder is thrashing around when the plane is inverted.  Is this related to the scaling issue?

  • Developer

     

         Thanks everyone for testing.

     

         I've just pushed ArduCopter-2.5.5 to the mission planner and source code is available in the downloads area (look for ArduCopter-2.5.5.zip).  It's just like the Beta with the exception that I also added the fix to the Tri tail servo reverse issue as reported during testing.

     

         All frame types were updated in the planner including the TradHeli and Y6.  I figured for the Y6, even though the TB_Ratio has temporarily gone missing (but will be back in 2.6), it's more important to get this scaling issue out there.

     

  • Thank you! Since I've gotten my Hexa I thought that I was brain damaged and unable to tune PIDs.  I loaded 2.5.5 and the thing now works perfect and is so stable.

    Thanks again.

  • Hi

    2.5.5-Beta is looking really good for me! Thanks for the good work!

    M

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