Help with P controller

VEX V5 General Discussion
1

Okay so we are currently using a claw for our robot and we and having troubles with tripping out motors when holding items tightly without claw. I would like to write a P controller for our claw so it automattically doesn’t move when items ar win it. I’ve written a PID controller before but that was the fly wheel last year and that was a constant hold of value. This year I am running the claw and it stops when i release a button so I don’t know how to set the target value using the button to open and close the claw. So if someone could help me with a layout of what I should do for this P controller that would really help.

2

Wouldn’t it just be easier to apply a braking pressure of 10-15 to hold all the items in? Or am I misunderstanding your issue?

3

That would help but I would like to use A p controller to now use as much power

4

Anything much lower than 10 will kind of be useless as far as actually holding in the objects. Do you have a specific reason for wanting to avoid 10 motor power? It has never caused motors to overheat in my experience.

5

I don’t want our claw to get move and open from stars hitting it when we move aorund the field even when we aren’t holding things

6

I’ll send you some sample code when I have some more time. Using a P controller is substantially better than just setting a motor power.

7

Here’s the sample code:


int target = 0; //target value for claw

float kp = 0.5;
float ki = 0.1;
float kd = 0.01;
//these are constants you will need to tune

int derivative = 0;
int integral = 0;
int lastError = 0;
//some variables necessary for PID; you can ignore these two as well as ki/kd if you only want a p controller
void clawPID(){
     error = SensorValue[claw] - target;
     integral += error;
     derivative = error-lastError;
     motor[claw] = kp*error + ki*integral + kd*derivative;
     lastError = error;     
}

task clawControl(){
     while(true){
          if(vexRT[Btn5U] == 1){
                motor[claw] = 127;
                target = SensorValue[claw];
          } else if(vexRT[Btn6D] == 1){
                motor[claw] = -127;
                target = SensorValue[claw];
          } else {
                clawPID();
          }
     }
}