I’ve written the following code. It’s a PID controller to have my robot turn 90 degrees left. I think I’m getting the hang of PID control. Couple questions I’ve got:

- I need to set a cap for my integral term. What should I cap the integral at?
- How can I use the integral term to correct steady state errors in this code? I don’t quite understand the function of the integral in this PID controller.
- I understand the function of the derivative and proportion constants. I don’t quite understand how the integral term will correct steady state errors. Maybe there’s an issue with my code regarding how the integral of error is calculated.
- I noticed that increasing kD (derivative constant) makes my robot oscillate more when getting closer to 90 degrees. Isn’t the derivative supposed to dampen oscillations?

```
// PID Constants and Variables
double kP=2;
double kD=2;
double kI=1;
double error_prior=0;
double integral_prior=0;
turnSensorUpdate();
double angle=((int32_t)turnAngle >> 16) * 360 >> 16;
double error = 90-abs(angle);
double integral=integral_prior+error*(10);
double derivative = (error-error_prior)/10;
integral = constrain(integral,-90,90);
double turnSpeed=kP*error+kI*integral+kD*derivative;
motors.setSpeeds(-turnSpeed, turnSpeed);
error_prior - error;
integral_prior = integral;
delay(10);
```