Two bad crashes in VTOL automission

Hello friends.
I have tuned and flown many VTOL drones. The main way I fly the drones is to take off vertically in QLOITER mode and transition to fixedwing flight by changing the flight mode to FBWA. I did this more than 100 times on 3 different types (40 kg gasoline engine VTOL drone, 10 kg electric power VTOL drone and 20 kg gasoline engine VTOL drone). It’s Important to say that I did all of this with Radiolink Pixhawk and there wasn’t any big problems.
Recently I switched to Cube and started to tune and fly a SwiftVTOL composite material drone. I did the tunings and QLOITER and Auto modes were working nice. After performing many flights, I started to do some automissions.

I plan my automissions like this:
VTOL_TAKEOFF -----> alt 20 m
DO_CHANGE_SPEED -----> speed 18 m/s
I did this about 5 times in 2 different days.
but the last one was a very bad crash. The drone took off and go to 20 m alt. Then changed the throttle to 95% and started the transition. after reaching transition speed, it flipped and crashed into the ground. I had “BAD AHRS” on HUD and EKF YAW RESET message in last flight.
Also I forgot to Calibrate Airspeed on last flight and the Airspeed was reading about 5 m/s on the ground. but I don’t think the Airspeed was the main problem. because I was calibrated the Airspeed on the first flight and haven’t changed the main battery in 3 flights. It means that the Cube wasn’t reset since the first flight. So the 5 m/s of Airspeed was maybe bacause of the wind that it was sensing.
I think the problem comes from the Cube :face_with_symbols_over_mouth: :face_with_symbols_over_mouth: :face_with_symbols_over_mouth: :face_with_symbols_over_mouth: but I’m not sure.

My config. is this:
4 x T-Motor U7 kv420 with 18"x6.1" CF Props for vertical flight.
1 x T-Motor MN4120 with 13"x9" Aeronaut fixed propeller for cruise.
1 x 8s7p 18650 Li-Ion battery for cruise.
1 x 6s1p 4500 mAh 75c Li-Po battery.

this is the telemetry log and flight control log download link:

It will be very helpful, if you share your experience and guesses about this issue.

It ever reached transition airspeed. During transition, motor connected to CH6 stopped and that caused the flip and crash.

1 Like

Thanks for your feedback.
Why that motor stopped?

Well, because it failed ? :smiley:
Could be ESC, wiring, motor winding… anything.

You say this because its output been saturated?

Yes, it is a normal response of the flight controller to trying counteract missing thrust.

I didn’t see that output saturation when checking the log.
If you see, I changed the flight mode to recover the drone, but the motors didn’t started working. There was no response.

Compare motor output with plane attitude.

It shows something. :joy:
But I didn’t see in real.

Thank you very much for helping.

motor on Ch6 are often in full throttle,
maybe ESC is being hot then desync, and it is causing the motor 6 stopped.
Just my thought.