PID Subsystem using direct PWM ouput

Technical Java
1

I am using a PID subsystem to control our arm. When I start the command to setToSetpoint(setpoint), the PID subsystem actually accesses the PWM port directly, and as I have already made an instance of that PWM port for teleop, I get a NullPointerException for a used PWM port. This stops our code, and is basically detrimental to all our PID controllers. Its worth noting that all of our motor objects are outside of the PID classes, mostly for organization. I am using custom methods to control those motors. These custom commands are perfectly functional, and are not the problem (We use them in teleop). How can I make it so that the PID subsystem does not “reach” into the other portions of the code, and just give the output. Thats it. Is there a workaround for this, or is this not common? I have had very little luck with PID control systems and I am getting fed up with how it has been implemented in the wpilibj libraries. Maybe making my own algorithm might work better.

2

Could you post your PIDSubsystem.

3 
package Subsystems;

import Hardware.Arm;
import Hardware.Sensors.Sensors;
import edu.wpi.first.wpilibj.command.PIDSubsystem;

/**
 * PIDarm - 
 * @author Joel Gallant
 */
public class PIDarm extends PIDSubsystem {
    private static final double Kp = 6.0;
    private static final double Ki = 0.0;
    private static final double Kd = 0.0;
    
    private Arm arm = new Arm();


    public PIDarm() {
        super("PIDarm", Kp, Ki, Kd);

        // setSetpoint() -  Sets where the PID controller should move the system to.
        // setStepointRange() - Sets the range that the setpoint may be in.
        // enable() - Enables the PID controller.
        setSetpointRange(arm.HIGH, arm.LOW);
    }
    
    public void initDefaultCommand() {
        // Set the default command for a subsystem here.
    }

    protected double returnPIDInput() {
        // Return your input value for the PID loop.
        return Sensors.getArmPosition();
    }

    protected void usePIDOutput(double output) {
        // Use output to drive your system, like a motor.
        arm.move(output);
    }
}

That’s as simple as it gets. Yet it does nothing.
For further detail into the PIDOutput…

    public void move(double speed){
        if(speed > -0.05 && Sensors.getBack() && Sensors.getArmPosition() < HIGH) {
            leftArm().set(speed*maxArmSpeed);
            rightArm().set(speed*maxArmSpeed);
        }else if(speed > 0.05 && Sensors.getFront() && Sensors.getArmPosition() > LOW) {
            leftArm().set(speed*maxArmSpeed);
            rightArm().set(speed*maxArmSpeed);
        }else {
            leftArm().set(0);
            rightArm().set(0);
        }
    }

That’s the method used for move arm.

leftArm() and rightArm() are as followed

private SpeedController leftArm;
    private SpeedController rightArm;
    
    private SpeedController leftArm() {
        if(leftArm == null) {
            leftArm = new Victor(PortMapping.armLeftChannel);
        }
        return leftArm;
    }
    private SpeedController rightArm() {
        if(rightArm == null) {
            rightArm = new Victor(PortMapping.armRightChannel);
        }
        return rightArm;
    }

Maybe I am not seeing something, but this should not create a new allocation of the PWM.
BTW PWM port 5 is leftArm, which is the one that gets allocated wrongly.

4

Hmm… The PIDSubsystem doesn’t do much behind the scenes, it just kind of takes your input and spits back an output.

It seems more likely to me that you have maybe created an arm somewhere else as well or maybe two PIDArms? Maybe you didn’t get rid of all the references to Arm in the code when you stuck in PIDArm…

That would be where I first look for the problem.

5

That’s what I found too. Thanks. :slight_smile:
Although Im not using PID anymore, as the buttons on smartdashboard do not properly implement the command.