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
Replies to This Discussion
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Permalink Reply by wilson javier madrid sossa on -
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.
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DeveloperPermalink Reply by Randy on -
Wilson,
Yes, it should be fine on the APM1 as well. The scaling bug fix won't have any effect nor most of the other bug fixes but it shouldn't hurt.
-Randy
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DeveloperPermalink Reply by R_Lefebvre on -
Yes, the developers would never knowingly do something to fix APM2, that breaks APM1. That's not to say that it never happens, but we try not to. When you upload new firmware from Mission Planner, it should auto-detect which board you have, and then upload the correct code.
In this case, the problem and fix does not affect the APM1 at all.
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Permalink Reply by Andke on -
ok, thank you for the fix.
The compass still expected to be inverted ? - right ? - no fix there ?
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3D RoboticsPermalink Reply by Chris Anderson on -
Andke: That should be fixed. See my post here.
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Permalink Reply by Andke on
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Thank you, - I commented on the post, as ,unfortunately, my compass is still reversed while "working fine" in terms of linear/relative movement, and tolerance to pitch & yaw. - you may say the sensor is performing as expected but it is reversed. (not a sign of hardware fault.)
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ModeratorPermalink Reply by Dean Wynton on -
I patched my firmware and had an issue that indicated reverse compass? when I switched to loiter it pictched forward and continued to increase pitch in steps until I switched back to stabilize, this only happened the one time on four flights. I have since updated via mission planner ( yesterday ) but due to the weather haven`t tested it. But I cannot reproduce the problem at home, I have tried starting in all positions but the compass remains pointing the right direction, I have not armed motors and tested?. The only thing I can see is when pointed dead north (360`) and then rotated 180` it does not then face dead south (180`) but around 130`? which could be a problem?
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ModeratorPermalink Reply by Dean Wynton on -
Just been out and tested with the firmware from mission planner and it seems to be much better than when I used the patch? I checked the az in status and it had gone down to around 1000, so I assume it was done correctly? Anyhow there is a definate improvement, 20mph winds today and I could hold it steady, even the loiter worked pretty good in the wind... And no sign of the compass bug yet? Well done to everyone that worked on it.. Cant wait for 2.6 :)
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DeveloperPermalink Reply by Randy on -
Dean,
There's only one additional fix that's in the mission planner version vs the 2.5.5-Beta patch that I posted ahead of the release. That fix is related to the TRI servo so it shouldn't improve the compass reversing issue (if it still exists).
Tridge and I are having a hard time finding any data on the compass reversing. We'd very much like to see a log (dataflash or tlog) if anybody experiences the problem.
-Randy
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ModeratorPermalink Reply by Dean Wynton on -
Maybe I missed out some of the patch somewhere? as it is much better now..
I haven`t been able to reproduce the compass bug or has it happened again so far? If it does I will be sure to send you a dataflash..
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ModeratorPermalink Reply by Dean Wynton on -
O.K been flying today and there was a strange incident when switching to loiter again, where it shot off in the wrong direction, so tell me exactly what file you need and how do I know which it is? I dont have wireless telemetry?
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Permalink Reply by wilson javier madrid sossa on
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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?.
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