The quadcopter uses ArduPilot 4.6.3 with 24” propellers. I was testing the mode transitions between stabilize and Loiter, and while in Loiter mode I lost control of the yaw and crashed. The event is near the end of the .bin file. Here’s the plot of the yaw vs time and Desired Yaw vs time curves, with the events annotated. Looks like the yaw is just drifting off…
The DataFlash logs (.bin) files are attached. I understand that Loiter mode relies on GPS and magnetometer. I am only using the external compass (Here 4 CAN GPS/Magnetometer), with the compass internal to the Pixhawk Cube Orange FC being disabled since I was having compass issues (“compasses inconsistent”) prior to this incident when both compasses were enabled. I had done a fresh compass calibration outside prior to this loss of yaw control issue.
Link to DataFlash (.bin) log file:
This loss of yaw control has happened twice to me now… I am getting a little desperate, any help is appreciated.
The first major problem I’ve seen when looking through the logs is that one particular output is saturated quite often, while others staying roughly at the same level.
This is quite easily a cause for yaw drifts, because out of the four axes of control (pitch, yaw, roll, thrust) yaw gives first (intentionally).
This does not seem to be a general overweight problem as outputs are generally centered at 1500. This is also not Loiter-related because it also happens in Stabilize.
It’s not only yaw, of course, that is affected during these excursions, other axes suffer too.
Tuning is generally not great (all PIDs are at defaults, no tuning ever has been apparently tried), but in yaw it is especially poor, see the general sloppiness below in a calm region.
To sum up, everything is bad, but the uncompensated rise and saturation of one of the outputs (and one particular output most of the time: the forward left motor) suggests to me a hardware failure of sort on that particular motor, propeller or ESC. This might include propeller slipping (maybe impossible on a 24") or overheating protection on an ESC, but lot of other options are also possible.
