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.

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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.

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.

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.

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!

Thanks Randy, I'll do the ac calibration again, and see how quickly the problem returns. I think this board may just be suspect though (it's an rctimer one), so if it keeps coming back it'll have to go in the junk pile.

After the ACC calibration it's working for now. I'll just keep a close eye on it.

New values are:


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