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 Jiro Hattori on -
I found myself, the reason of this behavior is that I left following line is commented ;
# define CONFIG_APM_HARDWARE APM_HARDWARE_APM2
Oh!
The scaling issue has been solved and found no other issues on 2.5.5 beta.
However, I do not know other changes and result.
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DeveloperPermalink Reply by Randy on -
Hattori-san,
Excellent, thanks for the feedback. I'm going to push it out to the MP on Monday morning tokyo time (Sun if you're on the west coast of the US) unless I hear some negative report.
-Randy
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ModeratorPermalink Reply by Dean Wynton on -
Thanks Randy will check it out
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ModeratorPermalink Reply by Dean Wynton on -
Seems to be working o.k on test bench, will take it out later today for a flight..
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ModeratorPermalink Reply by Dean Wynton on -
O.k the retro loiter on my current settings was not at all as good as the normal loiter, perhaps changing PIDs will help? and seems more twitchy when descending than it did before and the yaw on Tricopter seems less responsive? or a larger deadband?
Also I believe the reverse compass bug is still there, as I switched into loiter and it pitched forward and I left it to go to see what would happen? and it kept increasing the forward pitch until maximum so I switched it back to stabilize and bought her back.
Not doing any moaning, just trying to help with some faults I can see with a Tricopter, it may be different on something more inherently stable?
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Permalink Reply by Mark Murray on -
Hi
2.5.5-Beta is looking really good for me! Thanks for the good work!
M
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Permalink Reply by Dave C on -
Yup, my tri looks just as good upside down as it does the right way up. That's got to be an improvement :)
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Permalink Reply by Nicholas J Anderson on -
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.
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DeveloperPermalink Reply by Randy on -
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.
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Permalink Reply by Jake Stew on -
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?
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DeveloperPermalink Reply by Andrew Tridgell on -
I've just released ArduPlane 2.34 with the fix for this scaling problem
Cheers, Tridge
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