I’ve been developing a big hexacopter in Y6 configuration for a project. We’ve flown about 9 hours in total and covered almost 100 km with the hardware. While doing some operational testing we encountered weird behavior where the drone would reach a setpoint and kind of lose itself, do a turn and then start descending. It did this twice prior to this hard landing on two earlier flights (same day) but recovered quite quickly. For this reason I did not intervene with the drone during the descent, giving it the benefit of the doubt that it would correct itself. Sadly it did not and I had to intervene, I brought the throttle up to 100% but did not manage to safely land it, the drone just kept descending.
The log is here https://review.px4.io/plot_app?log=b362d811-b4a5-408b-a9db-3a329525d01c. It seems to be an IMU error and my hypothesis is that we’ve used up or flight controller.