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

Permalink Reply by Greg on May 14, 2012 at 5:06am

Jake,  I am no expert here but in answer to your question I noticed invensense, in their developer forum, talk about MPU-6000/6050 engineering samples which can operate in the +/-8g range i.e half the datasheet specification for the stated accelerometer full scale range. Invensene say the later production version of the device can operate in the +/-16g range.  Which I believe is moot given the APM2 code register selection uses the lower accelerometer readout scale in the 4g sensitivity range.  Of course one could speculate as to what is the real story regarding the release versions.  

At least the APM developers have the situation well under control.  Thanks all round to the dev team for picking this up and finding a way to automatically detect and apply the scaling patch accordingly.  

As an interesting side note the engineering samples would have a small ES marking on the chip according to the manufacturer.


DeveloperPermalink Reply by Randy on May 14, 2012 at 5:41am

And here is one of those chips!  This is off the very first APM2 that I got which was an early prototype (still has the older style baro too).  I wanted to put it side-by-side with the Revision D chips that are shipping now but the chip is covered by the daughterboard.  Anyway..something to look at..

Permalink Reply by Greg on May 14, 2012 at 5:55am
Randy thanks for the confirmation on the chips marked with an ES. Nice closeup.
Permalink Reply by Tomandy on May 12, 2012 at 2:39am

Randy wrote:

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.

But I am a newbie and is it possible to download the beta versions in the APm planner ?

Because I have the D version too.

 

Tomandy


DeveloperPermalink Reply by Randy on May 12, 2012 at 6:34am

Tomandy,

     I'm afraid it's not possible.  It'll be released shortly (in a day or so) through the mission planner in any case though.

-Randy

Permalink Reply by Tomandy on May 12, 2012 at 9:27am

Thanks for all your good work. I live in The Netherlands and I really like Arducopter.

 

Permalink Reply by Chapelat Daniel on May 12, 2012 at 9:17am

goodnight tomandy
You can download here:http://code.google.com/p/arducopter/downloads/list
then unzip and compile with Arduino
Attention: beta, personally I'll wait until Randy and the team are the official version
Daniel

Permalink Reply by Tomandy on May 12, 2012 at 9:25am

Thanks for your answer, but I think for a newbie, compiling is a step too far.


ModeratorPermalink Reply by Dean Wynton on May 12, 2012 at 3:09am

Cant get Tricopter yaw servo to reverse using 2.5.5 beta


DeveloperPermalink Reply by Randy on May 12, 2012 at 6:33am

Dean,

     Ah, right of course.  Let me take care of that tomorrow.  I'll probably add a new parameter to allow this.

-Randy


DeveloperPermalink Reply by Randy on May 12, 2012 at 8:54pm

Dean,

     I've checked in a change to hopefully properly fix the tri tail servo issue.  To be honest, we probably should use a new parameter instead of borrowing Channel 7's REV parameter but this was the least disruptive way to get it done now before the release.  I haven't uploaded the fix to the downloads area but if someone has a chance to check trunk before the release that would be greatly appreciated.

Permalink Reply by Jiro Hattori on May 13, 2012 at 12:08am

Randy

I becomes lazy to wait until upload to planner:)

I have just use Arduino relax to upload 2.5.5 beta on the new purple APM2. However, it is hard to setup radio from planner GUI or CLI.(no way to setup radio) This behavior has been seen in some occasion.

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