[Paparazzi-devel] IMU Failure/Freezing

[paparazzi_guy]

Hello everybody,

Thanks for all the previous help with my other forum posts. However, our
competition is closing in and we've noticed a significant problem with the
IMU. 

When I was outside with the plane on the ground, I noticed that the PFD in
the GCS had suddenly pointed in a random direction in the ground. The plane
was perfectly level and when I moved the IMU the PFD wouldn't react. I tried
turning the plane on and off multiple times and re-flashing the code, but
the PFD would keep pointing at the ground or at some other random point. In
the Messages section I could see that the values in the IMU_GYRO and
IMU_ACCEL tabs were not changing when I moved the IMU and were displaying
small values. After further testing we found out that IMU_ACCEL_RAW and
IMU_GYRO_RAW were still changing when the IMU was moving. Since we were
getting raw data, we think this is a software problem rather than a
hardware. But it might be too early to tell.

It's worth noting that when this was happening all other sensors were
working fine. This included the GPS, telemetry, airspeed sensor, RC, and
servos. Also, this error seems to occur only when I'm outside, but not every
time I'm outside. The longer I'm outside the greater chance of the error
occurring. The only way I know how to fix this problem is to bring the plane
inside, since the error never occurs inside. The walls to the building are
thermally insulated and basically create a faraday cage, meaning there is no
cell or GPS signal inside. I don't know if that is relevant or not. We will
keep researching but we haven't had any luck so far due to the
unpredictability of the problem. 

This problem was first noticed when we took our plane (equipped with the
autopilot) to our test field. It was the first time we had flown with the
autopilot and the error occurred the second time we flew with it that day.
When we flew the autopilot the second time the plane would start spiralling
to the ground and the PFD showed that the plane was facing straight up, even
though it wasn't.

Any input will be appreciated as we are trying to tie together many aspects
of the UAV before we leave for the competition in a couple of weeks. Thanks.

Matthew



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