Developer

MPU6000 scaling issue

 

     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.

Tags: ArduCopter, ArduPlane, MPU6000, Scaling

Views: 5148

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Replies to This Discussion


DeveloperPermalink Reply by Randy on May 8, 2012 at 7:07am

I forgot to mention that it would be good if you could do the regular APM set-up using the mission planner before your test..in particular doing an the Level would be good so we can get an idea as to how big your accel offsets are.  thanks again!

Permalink Reply by Tsahi Mizrahi on May 8, 2012 at 8:18am

 

 

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Permalink Reply by entropia666 on May 8, 2012 at 10:04am

At first: Pitch +- 180°

Then Roll +- 90° (right wing down first)

Then pitch +-90° (I don't remember the order lol)

Thank you for helping us!

Attachments:
Permalink Reply by andycross1 on May 9, 2012 at 4:12pm

Same problem goes from -1000 to +3000 hope this help, also includes the level offset.

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Permalink Reply by Mark Murray on May 8, 2012 at 10:59am

Here's mine!

M

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Permalink Reply by nicolas on May 8, 2012 at 2:53pm

Hello,

.tlog attached

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DeveloperPermalink Reply by R_Lefebvre on May 8, 2012 at 4:35pm

Ok, I have the issue as well.

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Permalink Reply by Bob Roach on May 8, 2012 at 7:47pm

I held my APM2 up-side-down (but still level) and confirm "az" is 3000. Tlog attached

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Permalink Reply by omgmayday on May 9, 2012 at 3:54am

Same issue here.

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DeveloperPermalink Reply by Randy on May 9, 2012 at 4:50am

Great, thank you very much!

Permalink Reply by Jiro Hattori on May 9, 2012 at 5:02am

Me too, Randy

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Permalink Reply by Andke on May 9, 2012 at 8:56am

Log attached.

Also; do you think the crazy gyro behaviour in this video can be related: http://youtu.be/PqriyQ-eOU8

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