Preventing Burned Out Motors

Since many people have burned out motors by putting too much torque on them, and the motors are expensive, I wrote a code that acts like a circuit breaker when too much torque is applied. It will temporarily stop the motor until the user presses a button to release it. All you need is an encoder. I have only written it for one motor, and because every robot is different, you will have to add more code to make it work for multiple motors. You can change the amount of torque that is needed before the motors stops by changing the value of the variable “threshold”. Here is the code:

#pragma config(Sensor, dgtl1,  quad,                sensorQuadEncoder)
//*!!Code automatically generated by 'ROBOTC' configuration wizard               !!*//

task clutch(){
  int quadPrev = 0; //stores previous encoder value
  float threshold = .01; //variable to increase or decrease the torque at which the motor stops.
  SensorValue(quad) = 0; //reset encoder
  wait1Msec(100); //initialize
    if(motor[port2] > 20 || motor[port2] < -20){ //checks if motor is running at a reasonable speed
      wait1Msec(100); //checks for stop and go movement
      while(motor[port2] > 20 || motor[port2] < -20){
        quadPrev = SensorValue(quad); //set quadPrev equal to the current encoder value
        wait1Msec(100);//let the motor run a little
        if(abs(quadPrev - SensorValue(quad)) < (abs(motor[port2]) * threshold)){
        //IMPORTANT PART: checks if the axle has moved the correct amount in proportion to the motor speed
          motor[port2] = 0; // stops motor
          hogCPU(); //stops task main from executing until the release button is pressed
          while(!vexRT[Btn6U]){ //this button releases the motor 
            motor[port2] = 0; //stops the motor which is not running correctly
            //insert all user controls except for the motor that is being stopped
          releaseCPU(); //starts running task main again

task main(){
  motor[port2] = vexRT[Ch1];
    wait1Msec(1);//needed for multitasking to work correctly

That’s it. If you implement this, let me know how it goes.

How does the code work? It’s not commented and I don’t really want to figure out each step… What’s it checking?

Sorry about that. It’s commented now. The code works by checking if the axle is turning the correct amount in proportion to the motor speed, and stops the motor (until the user presses a button) if it’s not.

We have used this code, and it works very well. If the wheel keeps locking up because of exessive friction (which shouldn’t happen in a well build bot), then the driver can just hold down the release button and drive like normal.