We were flight testing last Friday and had a fatal crash. The setup is as follows.
Flight Controller: Pixhawk 2.1
Firmware version: 1.7.3
TX: RadioLink AT9
RX: Radiolink R9DS
We have a companion computer where we change to offboard mode to send position setpoints, but not during the mission. I suppose that something triggered
OFFBOARD mode, and since the
COM_OBL_RC_ACT was set to 0 which is
POSCTL, the copter switches to
POSCTL for a split second and then drops to
STAB. Since the throttle was set to 0 from the TX, copter crashed with 0 thrust in about 1 seconds since it was about 10 meters above ground. While it was dropping, it switches to
POSCTL and back to
1) Might this offboard attempt be related to some noise on TX or RX side? The
RC_MAP_OFFB_SW was set to 9 so we also have an offboard switch on the transmitter. But never touched it really.
2) The TX flap was in the default position which is
STAB when the offboard reject happens, but since the
COM_OBL_RC_ACT is set to
POSCTL, shouldn't it stay that way? It seems that the RC tx somehow overrides all the commands(twice). This could be a critical bug which might need handling.