Claw dying after 30 seconds

I have a claw that keeps dying halfway through the match. The gear ratio is 1:3, and there is only one motor (we don’t have room for another). We have a button to pick the mobile cone up at 50% power and 100% power, though we mainly only use 50%. It works for about 30 seconds (3 mobile cones) then begins to lose power until it no longer moves. There are rubber bands mounted to help it clamp down harder so less power is needed, but it doesn’t seem to help. We think our problem is the PTC, but we have no solutions. Any ideas to what could fix it?

50 power is not needed at all and will overheat the ptc. Try 10-15 power.

It would help a lot in diagnosing your problem if you attached a picture, either way try to reduce friction in the whole system, one way to do this is to apply a legal lubricant to your gears.

Running the motor constantly anyways is not a good idea. We had a similar problem in Starstruck for a while. I recommend putting a potentiometer on the claw and using a simple P loop to hold the claw in its position. I would try something like this:

//in user control
int error = abs(SensorValue[clawPot] - tolerance);
if(error > tolerance) { //tolerance is some value you set to determine how far off the claw needs to be for the P loop to kick in
motor[claw] = kp * error; //kp is some constant - usually some small number less than 1

This should help keep your claw closed and keep it from burning out because it will not apply a constant force. Instead, it will only apply a very small amount of power, and will only run the motors when the error is big enough to be considered a problem.
You will need to carefully tune


to make sure that it is as large as possible without letting the cone fall out. This will cause tour motors to run the least.

we had same problem - here’s the code we use to fix it our issue:
if(vexRT[Btn6D] == 1) //OPEN
motor[clawMotor] = 100 ;
motor[clawMotor] = 0; //…stop the Motor.
this way we close the jaw for 1/2 second and hope gearing / resign of jaws do the rest. 3:1 I imagine you’re find but we use elastic to favor jaws being closed.

Also we find the H-Bridge (ports 1 & 10) to be very unreliable & susceptible to stalling & try to stay away from using them

Good luck!

We shall try using these programming approaches with our robot. Thanks so much for the helpful info! We replaced the motor on the claw and tightened the mount of the claw so that it was more parallel to the ground. Thus, the mobile goals don’t slip out unintentionally. It seems to have worked on Saturday at our competition and hopefully will stand up. Thanks again everyone!