Originally Posted by rgburrill

I'll say in advance I don't know anything about JR radios but I do know about electronics so this is just an educated guess. Since the trainer is merely providing the stick inputs for the master it is likely the throttle output of the trainer isn't the same as the throttle output the master normally provides. It could be reversed. It could just have different endpoints. In any case it is possible your ESC is not seeing a zero value when you have the trainer throttle at zero and, therefore, not enabling the motor output. I would connect a servo to the throttle line and see if it works.