stalled motor need help

we need some help our motor has always work fine on its wheel but at competition the right one always stalls up and wont move at all this cost us some points. if you can give me some answers to this that would be great. this problem was only when we where hooked up to the competitions wire to control our remote and once on the practice field.

Hi! Our robot had a similar problem. It turned out that the axle kept slipping out of the motor, so we just pushed the axle in as far as it would go, added a shaft collar and kept a close eye on the motor.

This is most likely a PTC issue. Here is a detailed inspection of the PTCs found in Vex motors and Cortexes. Essentially what happens is that as motors are put under load, they tend to heat up. Eventually they dangerously hot, putting them at risk to permanent damage (melted plastic, burned out electronics, etc.). To prevent this, Vex motors have PTCs built in to them. When they get too hot, they will cut off power to the motor for ~10 seconds, depending on how long it takes to cool down. If there is too much friction or too little torque in your drive, the motors will overheat and trip the PTC. When this happens during a competition, it is best to turn off the affected motor(s) and wait 10 seconds before using them again. To actually fix the issue, you can do a number of things:

  • reduce friction
  • add torque (another motor or a slower gear ratio)
  • don’t supply as much power to the motor (multiply the joystick value by 0.6 or so)

Probably make sure the shaft is connected first, though. That’s a much simpler fix.