Sudden uncontrollable yaw rotation while hovering


I am writing to seek assistance with a perplexing issue that occurred while flying my multirotor using PX4.

Please accept my apologies if my writing appears awkward, as I am not a native English speaker.

First, let me provide information about the hardware being used:

Frame: X4 Quad

Motor: Hobbywing X8

Propeller: 3090

FC: Pix32v6

Battery: 12cell

After assembling the aircraft, it flew normally in Manual, Altitude, and Position flight modes, including at low speeds. The auto-tuning process was completed without any issues, and there seemed to be no problems while hovering.

However, during the subsequent flight, the aircraft suddenly lost yaw control and crashed while rotating in a specific direction. The flight log at the time is as follows:

According to the log, the aircraft outputted maximum PWM in the opposite direction of rotation, and not only yaw control but also roll and pitch control were virtually impossible, leading me to believe that there might be a motor malfunction.

Yet, during the next flight, a baffling event took place. The same symptom occurred while hovering, but the direction of rotation was reversed. The flight log at the time is as follows:

Since the same symptom occurred but with an opposite direction of rotation, if it were a motor problem, the problematic motors should have been the ones rotating in opposite directions in both flights. However, the motors were almost new, and the probability of simultaneous failure in two motors seemed low.

I am posting this message as I suspect that there might be a hardware-related issue with Hobbywing X8 or Pix32v6, or a PX4 setting issue that I am unaware of.

One point of concern is that when I calculated the thr_mdl_fac value based on the Hobbywing X8 datasheet, the result was 1.02, so I arbitrarily applied a value of 0.4. I wonder if this value might affect the operation of the motor and the speed controller.

Thank you for taking the time to read this lengthy message, and I eagerly await your responses.


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Thank you for giving context and some explanation to what happened. And sorry to hear about the crash.

I looked at the logs and Iโ€™m also puzzled, and donโ€™t have an explanation yet. Iโ€™m going to tag @MaEtUgR hoping that he might have some insight, especially regarding the thr_mdl_fact.

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