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?
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I´ve got n RTFHawk ordered in April with lsm303D issues.
Obviously there is an issue. I'm not suggesting there isn't but I wonder how many are caused by moving the copter while it's booting up?
Hello everyone,
I have had similar pre-arm issues with my Pixhawk, but I have also experienced two mid-air accelerometer failures leading to my quadcopter crashing. I thought I'd share the details and logs with the community, hoping that they will be useful in diagnosing the problem.
I'm using an original Pixhawk from 3DR, with 3.2 firmware. The unit is powered by a combined BEC and power distribution board (HK Pilot Power VI Module - http://www.hobbyking.com/hobbyking/store/__68694__HK_Pilot_Power_VI...), with functionality corresponding to the 3DR power module. During testing I have used 4S LiPo batteries.
During setup I have experienced problems calibrating the accelerometer, as well as prearm checks failing, just like other people have reported. In addition to the "bad accel health" warning, I have also seen "bad gyro health", "alt disparity", and "compasses not consistent". Originally I had the Pixhawk powered with both the power module mentioned above and an additional backup 5V BEC. After disconnecting the backup BEC the problems seem to be at least partly solved, and I'm able to arm the copter. Having both USB and battery connected also seems to result in prearm checks failing. Does anyone have any idea why using two 5V power sources should pose a problem? After all, the Pixhawk has been designed with this option in mind.
After setup, I have been able to fly the quadcopter successfully a couple of times without any failures, using both Stabilize, AltHold and Loiter modes.
Now, to the crashes: Both of these happened in cold weather (approx -5 to -10 C), which seems to be one of the main candidates for why the problem arises.
Crash 1: I flew the copter for just a couple of minutes, mostly in stabilize mode, when it suddenly accelerated away from me. I cut the throttle and it crashed in the woods out of my sight. After analyzing the log I have found the reason for this behavior: The IMU1 (MPU6000) accelerometer values suddenly jump all over the place, causing the stabilize mode algorithm to tilt the copter and fly away. This is seen in the screenshot below. I have checked the IMU2 values as well (not included in screenshot), and these appear normal.
Crash 2: I attempted to run the AutoTune PID tuning while in AltHold mode. After a couple of minutes, the copter suddenly drops like a rock out of the sky. After analyzing the log I found that the z axis on the IMU1 accelerometer had very large negative values. This in turn resulted in very high values for the altitude rate of ascent, and the AltHold algorithm cut almost all throttle to counteract this. The screenshot below shows both the IMU1 accelerometer values, the barometric altitude and the altitude estimate. Again, the IMU2 values appear to be fine for this case.
I have attached the logs for both the crashes.
Basically, I think that the copter would fly fine using only the IMU2, and the fix included in the 3.2.1 firmware ("improved MPU6k health monitoring and re-configuration in case of in-flight failure") may very well help me. I will cross my fingers and try that, and report here if I find anything useful.
If this is indeed a hardware failure, it seems odd that so many are experiencing the same problems. Was there a bad batch of accelerometers out there when these Pixhawks (and clones) were produced? Could I expect the problems to disappear if 3DR is willing to replace the unit?
Please let me know if there is anything else I can do to help diagnose or solve these problems.
2015-01-23 23-13-30 Crash1 - AccFailure - lost control.log
2015-01-28 13-54-27 - Crash2 - AccFailure - FaultyAltitudeEstimate.log
A quick follow-up, although the discussion has now moved on:
I contacted 3DR regarding the crashes described above, and they confirmed that the Pixhawk has an MPU6000 failure. They will be sending me a replacement.
After reading this thread I realized I am not the only one experiencing this issue. I have a new Iris+ that is about a month old. 3DR Pixhawk with 3.2 firmware. I was able to fly it successfully for a dozen or so flights with 3.2iris firmware that it came with. The prearm problems started after updating to 3.2. Currently I get a prearm failed accels inconsistant or prearm failed accels not healthy in MP. I have tried to calibrate accel at least 6 time and the calibration always fails. The last flight was acting strange and then it just flew away and crashed into my neighbors house. I don't know how to read the log files so I attached the last flight which ended in the crash for to add to your database.
2015-01-22 16-51-14.tlog
Hi Steve,
Thanks for posting that log. That is indeed a MPU6000 hardware failure, and the serial number shows the board was manufactured on 9th of October.
I think you should contact 3DR and see if you can get the Pixhawk replaced.
Cheers, Tridge
Thanks Andrew,
I have contacted 3DR and they are supposed to be sending me a FedEx shipping label.
Regards,
Steve
Tridge,
How are you able to extract the SN from a tlog?
Regards,
Nathaniel ~KD2DEY
Good idea, Staq. My original Pixhawk was purchased in September 2014. This one had a faulty accelerometer and was never flown. I received a replacement in January 2015, this is the board which I'm struggling with now. I'm able to arm, but there seem to be in-flight accelerometer errors.
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