Hi all,
During a flight test, my quadcopter suddenly experienced instability while descending forward. Visually, it appeared that the right side propeller stopped spinning, which caused a rapid loss of yaw and roll stability.
I analyzed the log and observed:
Around 19:55 (log time), Motor 1 output dropped to nearly zero while the other motors remained active.
Yaw and Roll control commands spiked significantly right after, suggesting the autopilot attempted to compensate.
Z-axis gyro data shows a sudden angular velocity spike consistent with a yaw disturbance.
Vibration levels were already high during flight and increased further around the event.
Magnetic field (X/Y) showed irregular fluctuations throughout the flight.
Flight Review Log:
Hardware Setup:
Flight Controller: Pixhawk 6X
Motors: TYI 5008 KV335
ESCs: Hobbywing XRotor 40A
Battery: 6S LiPo
GPS Module: u-blox M9N
Video/Telemetry**: OpenHD (Raspberry Pi + WiFi)
Do you think this issue is more likely caused by:
- ESC failure or thermal shutdown?
- Loose motor connection or power line?
- Magnetic/electrical interference?
- Flight controller output signal issue?
I would really appreciate any insight or debugging suggestions. Thanks in advance!
I agree with your analysis. PX4 tries to compensate.
I would expect this to be a mechanical or electrical problem, or motor/ESC loosing sync, etc. Hard to say which of these it is.
Do the motors work again, any chance you can run them on the bench for a bit to check for any similar drops?
By the way, roll control looks noisy, I suggest to detune that a bit.
Thanks for your feedback!
I tested the motor on the bench without a propeller, and it seems to work fine.
There were no sudden drops or sync issues, and it responded normally to throttle commands over a few minutes.
Do you have any suggestions on how I can further test this?
Should I try running the motor with a propeller under light load and monitor temperature or current?
Could this be an intermittent ESC sync issue that only triggers under certain air resistance?
Is there a good way to test for electrical connection stability, such as loose wires or cold solder joints?
I’m open to any debugging advice to help pinpoint whether this is a hardware or tuning-related problem.
Thanks again!
Is your idle (lowest) throttle fast enough? It shouldn’t be stopping or starting to stutter.
Thanks for the suggestion!
Currently, my PWM settings are:
- PWM_MAIN_MIN = 1150
- PWM_MAIN_MAX = 1950
- PWM_MAIN_DIS = 1000
At the current PWM_MAIN_MIN value, all four motors do not start spinning when armed.
From what I understand, this likely means the idle throttle is too low, and the motors might stop or stutter during low-throttle situations like descending.
My plan is to gradually increase PWM_MAIN_MIN until all four motors spin smoothly at idle without stuttering.
After that, I will perform a short flight test to check if the issue is resolved.
Does that sound like the correct approach?
Yes, that’s exactly right.
