Climb/drop when moving forwards/backwards in alt hold

I have a weird issue on only one of my APM2.5 boards where in alt hold, the copter will climb when I move forwards, and drop when I move backwards. This climb/drop happens as soon as input is given.

Is it possible that I have a bad board? I am having trouble interpreting the logs to tell what exactly is going on. I have a dataflash log with IMU logs enabled which shows the issue on a short flight today.

Running 3.1 RC5, but this has happened with the last few versions I have run.

2013-10-27 10-12 224.log

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Replies

  • Developer

    So this is caused by having the accelerometer calibration incorrect.  So the parameters involved would be:

     INS_ACCOFFS_X    0.135
     INS_ACCOFFS_Y    0.26
     INS_ACCOFFS_Z    0.53
     INS_ACCSCAL_X    1.007
     INS_ACCSCAL_Y    0.993
     INS_ACCSCAL_Z    0.979

    In particular it's probably the INS_ACCOFFS_Y value and it may be changing over time.  I suspect if you re-do just the accelerometer calibration it'll be fine for a while.  I have no idea why it would be changing over time though but doesn't sound good!

  • Ok, yeah I have tried giving this copter a complete erase/reset and setting up from scratch, and it starts off flying OK, but then eventually this problem returns intermittently after a few flights, and eventually happens all the time. If I swap this particular APM out with another I have, it works perfectly.

  • Developer

    You appear to have the APM tilted slightly nose down during flight. I would have to spend an hour or so to go through the code ot fully understand the implications of the way we do our leveling so I can't give you a precise answer about how to fix this.

    I would suggest redoing your accelerometer calibration and making sure your APM is mounted horizontal and your propellers are all horizontal.

  • It looks like there's a bad Y/Z accel reading in the logs at line 1998 which I needed to trim out before the graphs would display correctly, but I don't know how this is related. I also had to trim out the last IMU line which had very high values.

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