A few users, myself included, appear to be having issues calibrating accels and/or arming when using APM 3.2 on a Pixhawk. I see posts here and there, but thought it may be best if those having the issue could all 'check in' to one post so that the developers can see how widespread the issue is and gather data.
My Pixhawk will arm occasionally, and will even fly successfully. Occasionally however it will not arm and I will receive the pre-arm error "Accels not healthy". A few days ago I was able to arm and fly thorugh one lipo, then after landing and swapping batteries I could not arm due to this reason. I have attached the logs from the successful flight, as well as the failed pre-arm logs, to this post.
As you can see from these images there is something amiss with IMU2. This is a snippit from the good flight, showing values for AccX on IMU1 and IMU2:
and here are the same values on the second attempt, pre-arm.
In the 3.2 release thread a few users had mentioned the issue and Randy advised to set the log_bitmask to "131070" so that it will log everything including the pre-arm checks. I encourage others having the issue to do the same and share the logs and experiences here so that we can find out what is going on here - is there a bad batch of Pixhawks in the wild that only now show the hardware errors due to something new in 3.2, or is there an issue in the APM software?
Replies
I've noticed the IMU mismatch seems to be getting worse over time. Recalibrating the accels doesn't help. Today it was 1.3. It appears the Z axis is the culprit, and IMU2 has considerably more noise compared to IMU. I have not had a failure in the air, but while connected to MP via USB today it gave a bad health warning.
Is my Pixhawk dying? Is it time to think about replacing it? I've never had a problem arming if that means anything.
Try to connect full power also. For me it looks that USB power source is not strong enough to drive all connected stuff and thus generate this errors.
The error doesn't bother me. It's the IMU Mismatch. There's obviously a divergence between IMU and IMU2.
I had a similar experience with increasing IMU mismatch numbers. Then I build a standoff vibration board , with ear plugs, and my log readings are excellent (.25-.35).
Which axis had the mismatch? The vibration levels on all 3 axes are good, so I don't understand why there is a mismatch only on the z, but obviously must be missing something. Why wouldn't both IMU's be reading the same vibration level? Are they at different locations on the Pixhawk board, and possible one location is sensing more vibration than the other?
The copter is a Sky Hero Spy 750, quite a robust frame. The motors and props are balanced.
It wasn't easy (for me anyway) to come up with a simple mounting platform for the FC as there is large access hole where the ESC wires come through. On the top plate I attached 4 rhino glass standoffs secured with 10lb double sided tape, then Zeal gel ~1/2" squares under each corner of the Pixhawk. I've read mixed opinions about the zeal gel, but it seemed to work ok, however the IMU mismatch has become inconsistent from flight to flight. In fact I the Zeal gel did come loose on two corners so used Goop adhesive to better secure them.
Looks like I need to do some homework on trying better anti-vibration solution, although I'm still puzzled why both IMU's don't measure the same whether the mounting is good or bad.
I'm not a log reading guru. However, my experience was similar; The individual readings looked pretty good, but I still received the IMU mismatch.The auto result always came with a recommendation to check vibrations...
My present readings, with new V-board, are much tighter and smaller than your screen shot.
I believe we are getting better info with the 3.2.1.
Ok, you've convinced me to redo my setup.
Here's my DIY V-Board. I use 3M 25pound tape to hold the plugs to the top plate. You maybe able to cut your board large enough to span the opening in your top plate.
Oops: Getting OT. Admin, please feel free to delete as needed.
Hi,
Please check my log file.
Videos of the moment you can see here: https://www.youtube.com/watch?v=2eA_v7bC2kg&feature=youtu.be
I have Pixhawk 3.2.1 from 3dr.
174.BIN
Can someone please solve my dilemma...I need another Pixhawk,original only...my first one I bought at Kopterworx(very near me) and now I would buy one from official supplier in Germany http://www.uav-store.de/autopilot-1/pixhawk/ Is there any way I can determine if boards they got months ago does not have problems(serial number maybe)?Can I ask for some kind of testing before purchase?
...or is my only choice to order from direct from 3DR what will cost me much more in $ and time..thank you
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