Can someone explain this code?

Technical Java
1

Could someone explain what is going on in this code?

public class Drivetrain {

Talon talon1 = new Talon(1);
Talon talon2 = new Talon(2);
Talon talon3 = new Talon(3);
Talon talon4 = new Talon(4);
Talon talon5 = new Talon(5);
Talon talon6 = new Talon(6);

DoubleSolenoid shifter = new DoubleSolenoid(1, 5, 6);

Encoder leftEncoder = new Encoder(10, 11);
Encoder rightEncoder = new Encoder(13, 14);

public Drivetrain(){
    leftEncoder.start();
    rightEncoder.start();
}

//DigitalInput port14 = new DigitalInput(14);
public void arcadeDrive(double moveValue, double rotateValue){
    double leftMotorSpeed = 0, rightMotorSpeed = 0;
    
    rotateValue = -rotateValue;
    moveValue = limit(moveValue);
    rotateValue = limit(rotateValue);
    
    if (moveValue > 0.0) {
        if (rotateValue > 0.0) {
            leftMotorSpeed = moveValue - rotateValue;
            rightMotorSpeed = Math.max(moveValue, rotateValue);
        } else {
            leftMotorSpeed = Math.max(moveValue, -rotateValue);
            rightMotorSpeed = moveValue + rotateValue;
        }
    } else {
        if (rotateValue > 0.0) {
            leftMotorSpeed = -Math.max(-moveValue, rotateValue);
            rightMotorSpeed = moveValue + rotateValue;
        } else {
            leftMotorSpeed = moveValue - rotateValue;
            rightMotorSpeed = -Math.max(-moveValue, -rotateValue);
        }
    }
    
    //Setting talon values
    talon1.set(-rightMotorSpeed);
    talon2.set(rightMotorSpeed);
    talon3.set(rightMotorSpeed);
    talon4.set(leftMotorSpeed);
    talon5.set(-leftMotorSpeed);
    talon6.set(-leftMotorSpeed);
}

protected static double limit(double num) {
    if (num > 1.0) {
        return 1.0;
    }
    if (num < -1.0) {
        return -1.0;
    }
    return num;
}

public void highGear(){
    shifter.set(DoubleSolenoid.Value.kReverse);
}

public void lowGear(){
    shifter.set(DoubleSolenoid.Value.kForward);
}

public void brake(){
    
}

public int getRightDistance(){
    //return port14.get();
    return rightEncoder.get();
}

public int getLeftDistance(){
    return leftEncoder.get();
}

public void resetEncoders(){
    leftEncoder.reset();
    rightEncoder.reset();
    
}

}

2

What behavior is it exhibiting that doesn’t make sense?

It looks relatively normal, but could you add code tags around it so it preserves indentation? e.g.

printf("Hello World");

code ] opens
/code ] closes
(Eliminate the spaces from the tags)

3

The code works fine, I just don’t understand it and I am unable to contact the guy who wrote it.

The code shown is for a 6 wheel west coast drive bot

4

Here’s what I’ve interpreted so far. The rotate left/right may be flipped.

This is a rather strange convention.
leftMotorSpeed = moveValue - rotateValue;
rightMotorSpeed = Math.max(moveValue, rotateValue);

It’s probably trying to make sure the right motor is going faster than the left (i.e. turning left), but regardless this is probably not the ideal way to code this.


public class Drivetrain {

	//right speed controllers
	Talon talon1 = new Talon(1); //front
	Talon talon2 = new Talon(2); //middle
	Talon talon3 = new Talon(3); //rear
	
	//left speed controllers
	Talon talon4 = new Talon(4); //front
	Talon talon5 = new Talon(5); //middle
	Talon talon6 = new Talon(6); //rear
	
	DoubleSolenoid shifter = new DoubleSolenoid(1, 5, 6);
	
	Encoder leftEncoder = new Encoder(10, 11);
	Encoder rightEncoder = new Encoder(13, 14);
	
	public Drivetrain(){
		leftEncoder.start();
		rightEncoder.start();
	}
	
	//DigitalInput port14 = new DigitalInput(14);
	public void arcadeDrive(double moveValue, double rotateValue){
	double leftMotorSpeed = 0, rightMotorSpeed = 0;
	
	rotateValue = -rotateValue; //x axis value from joystick. inverted to get the correct rotation direction
	moveValue = limit(moveValue); //y axis value from joystick. make sure its between -1 and 1
	rotateValue = limit(rotateValue); //make sure the rotation value from before is between -1 and 1
	
	if (moveValue > 0.0) {
		//driving forward?
		if (rotateValue > 0.0) {
			//turning left?
			leftMotorSpeed = moveValue - rotateValue;
			rightMotorSpeed = Math.max(moveValue, rotateValue);
		} else {
			//stopped or turning right?
			leftMotorSpeed = Math.max(moveValue, -rotateValue);
			rightMotorSpeed = moveValue + rotateValue;
		}
	} else {
		//driving backward or stopped
		if (rotateValue > 0.0) {
			//turning left?
			leftMotorSpeed = -Math.max(-moveValue, rotateValue);
			rightMotorSpeed = moveValue + rotateValue;
		} else {
			//stopped or turning right?
			leftMotorSpeed = moveValue - rotateValue;
			rightMotorSpeed = -Math.max(-moveValue, -rotateValue);
		}
	}
	
	//Setting talon values
	talon1.set(-rightMotorSpeed); //invert the front right speed controller (probably because the leads were swapped)
	talon2.set(rightMotorSpeed);
	talon3.set(rightMotorSpeed);
	talon4.set(leftMotorSpeed); 
	talon5.set(-leftMotorSpeed); //invert the center left speed controller (probably because the leads were swapped)
	talon6.set(-leftMotorSpeed); //invert the rear left speed controller (probably because the leads were swapped)
	}
	
	protected static double limit(double num) {
		if (num > 1.0) {
			return 1.0;
		}
		if (num < -1.0) {
			return -1.0;
		}
		return num;
	}
	
	public void highGear(){
		//retract pneumatic
		shifter.set(DoubleSolenoid.Value.kReverse);
	}
	
	public void lowGear(){
		//extend pneumatic
		shifter.set(DoubleSolenoid.Value.kForward);
	}
	
	public void brake(){
	
	}
	
	public int getRightDistance(){
		return rightEncoder.get();
	}
	
	public int getLeftDistance(){
		return leftEncoder.get();
	}
	
	public void resetEncoders(){
		leftEncoder.reset();
		rightEncoder.reset();
	
	}
}
5

That part is a copy of the WPILib arcadeDrive method. You can see how it works here: http://www.chiefdelphi.com/forums/showpost.php?p=1133680&postcount=11

6

From a style and code neatness standpoint, might I suggest putting your right talons in an array and your left talons in another? Then you can set an entire side’s speeds with a for loop like so:


for (int i = 0; i < left.length; i++)
{
   left*.set(1);
}

or now with the roboRIO (Java SE 8), with a for each loop…


for (Talon t : left)
   t.set(1);

then put it in another method for easy use…


public void setLeft(int speed)
{
   for (Talon t : left)
      t.set(speed);
}

or even a more general method for less code…


public void setSpeed(Talon] tarray, int Speed)
{
   for (Talon t : tarray)
      t.set(speed);
}

and finally, work in the inversion…


public void setSpeed(Talon] tarray, int Speed)
{
   for (Talon t : tarray)
   {
      if (t.equals(talon1) || t.equals(talon5) || t.equals(talon6))
         t.set(-speed);
      else
         t.set(speed);
   }
}

We handle setting our drivetrain speed in a similar fashion.*

7