Full engine stop

Good evening! We work with copter 3.1 and testest algorithm of yaw. Out copter turns left, but can’t turns right. What may be the reason? One of four engines is full stopped when copter turing right, but this should not happend. How to set a minimum threshold firmware PWM signal?

@Makhonin,
How about providing either tlogs and/or data flash logs to help troubleshoot your issue.
Regards,
TCIII GM