Hi
I had a frightening occurrence today where my 250-sized pixhawk / 3.2 quad suddenly started behaving very erratically in loiter mode -- rapidly gaining altitude.
After spending some time graphing dataflash logs, It seems that the issue began with an as-yet-unexplained sudden increase in vibration. The graph snippet below shows AHRS altitude in orange, and Z axis IMU in blue. The issue started right when the orange line shoots up for the first time, shortly before I switched to stabilize mode to try to recover.
I'm trying to understand how I can find backup in the logs for correlating these two events... If the vibrations were making the IMU think the altitude was incorrectly low, I could understand this, but I can't see that happening. Not included in the graph below is the Barometer altitude reading, but it correlates with the AHRS altitude.
Log also attached.
Thanks
Replies
Accel z if bad will affect altitude like you are seeing. The brain tries to estimate altitude based on the acceleration as well as using baro and gps altitudes.
You need to figure out what the vibration is and fix it.
Understood; I'll deal with the vibrations (on a side note, it's still a mystery to me because it started 8 minutes into the flight, and nothing was loose when it came home).
Although I understand conceptually the cause and effect implied, I'm trying to find evidence in the log that links the vibrations to the rapid increase in altitude. I would have expected the AHRS altitude output to drop quickly then attempt to compensate, but I don't see that.
http://copter.ardupilot.com/wiki/common-diagnosing-problems-using-l...