In ArduSub 4.0.x, and possibly also the current 4.1.0-beta MOT_PWM_* are ignored, and RC3_* are always used (which is a bug). In 4.2.0-devel if MOT_PWM_* are 0 then RC3_* are used (as per the MOT_PWM_* descriptions), otherwise the MOT_PWM_* values are used.