Deflector Flip

This example discusses a subsystem called a Deflector. It may be hard to visualize this, so here is an animation describing how it works:

The gear comes down the chute, but there is a deflector to make sure it doesn’t land on the top of the robot. But since the gear can get stuck on that deflector, there is a pneumatic cylinder that can push the deflector up to dislodge the gear.

Design

In this example, the design of the deflector is a piece of plastic, with a pneumatic cylinder hooked up to a double action solenoid.

Setting the solenoid to forwards causes the deflector to go upwards, and setting the solenoid to reverse causes the deflector to go downwards.

When the operator presses the START button, the deflector should go up, wait 0.25 seconds, and then come back down.

Subsystem methods

This guide assumes that there already is a Deflector subsystem, and to set the deflector solenoid, you simply need to write:

Deflector.DEFLECTOR_SOLENOID.set(DoubleSolenoid.Value.kForward);

We also assume that there are already commands called DeflectorUp and DeflectorDown that set the deflector up and down, respectively. These commands can be as simple as:

public class DeflectorUp extends InstantCommand
{
    public DeflectorUp()
    {
        super();
        // Use requires() here to declare subsystem dependencies
        requires(Robot.deflector);
    }

    // Called once when the command executes
    protected void initialize()
    {
        Deflector.DEFLECTOR_SOLENOID.set(DoubleSolenoid.Value.kForward);
    }
}

public class DeflectorDown extends InstantCommand
{
    public DeflectorDown()
    {
        super();
        // Use requires() here to declare subsystem dependencies
        requires(Robot.deflector);
    }

    // Called once when the command executes
    protected void initialize()
    {
        Deflector.DEFLECTOR_SOLENOID.set(DoubleSolenoid.Value.kReverse);
    }
}

On how to create this subsystem, see Creating a subsystem.

We also assume that OI already has a Joystick named operator, and that the START button on the operator’s controller is button 11.

On how to use OI, see OI.

Writing the command

Once you create the DeflectorFlip command group, you’ll get a blank command group template like this:

package org.usfirst.frc.team93.robot.commands;

import edu.wpi.first.wpilibj.command.CommandGroup;

/**
 *
 */
public class DeflectorFlip extends CommandGroup {

    public DeflectorFlip() {
        // Add Commands here:
        // e.g. addSequential(new Command1());
        //      addSequential(new Command2());
        // these will run in order.

        // To run multiple commands at the same time,
        // use addParallel()
        // e.g. addParallel(new Command1());
        //      addSequential(new Command2());
        // Command1 and Command2 will run in parallel.

        // A command group will require all of the subsystems that each member
        // would require.
        // e.g. if Command1 requires chassis, and Command2 requires arm,
        // a CommandGroup containing them would require both the chassis and the
        // arm.
    }
}

In the javadoc at the top, describe what this command does.

/**
 * This command group sets the deflector up for 0.25 seconds, and then sets it back down.
 * It is designed to dislodge gears off of the deflector.
 */

Then, the constructor is where all of the command adding goes. We need to set the deflector up, wait 0.25 seconds, and then set the deflector down. This can be accomplished using the DeflectorUp(), WaitCommand(0.25), and DeflectorDown() commands. And, since we want to execute these one after the other, we use addSequential for all of these.

You can also delete the autogenerated comments in the body of the constructor if you like.

Now, your command instead looks like this:

package org.usfirst.frc.team93.robot.commands;

import edu.wpi.first.wpilibj.command.CommandGroup;

/**
 * This command group sets the deflector up for 0.25 seconds, and then sets it back down.
 * It is designed to dislodge gears off of the deflector.
 */
public class DeflectorFlip extends CommandGroup
{
    public DeflectorFlip()
    {
        addSequential(DeflectorUp());
        addSequential(WaitCommand(0.25));
        addSequential(DeflectorDown());
    }
}

That’s all there is to the command group. It’s done.

Running the command

Now, go into the OI class. We need to set the DeflectorFlip command to run whenever the operator presses the START button.

public static Joystick driver;
public static Joystick operator;

public OI()
{
    driver = new Joystick(0);
    operator = new Joystick(1);

    Button deflectorFlipButton = new JoystickButton(operator, 11); // START button
    deflectorFlipButton.whenPressed(new DeflectorFlip());
}

And that’s it! Now, whenever the operator presses START, the deflector will flip up and down, and dislodge any gear stuck on it.

Final code

DeflectorFlip

package org.usfirst.frc.team93.robot.commands;

import edu.wpi.first.wpilibj.command.CommandGroup;

/**
 * This command group sets the deflector up for 0.25 seconds, and then sets it back down.
 * It is designed to dislodge gears off of the deflector.
 */
public class DeflectorFlip extends CommandGroup
{
    public DeflectorFlip()
    {
        addSequential(DeflectorUp());
        addSequential(WaitCommand(0.25));
        addSequential(DeflectorDown());
    }
}

DeflectorUp

public class DeflectorUp extends InstantCommand
{
    public DeflectorUp()
    {
        super();
        // Use requires() here to declare subsystem dependencies
        requires(Robot.deflector);
    }

    // Called once when the command executes
    protected void initialize()
    {
        Deflector.DEFLECTOR_SOLENOID.set(DoubleSolenoid.Value.kForward);
    }
}

DeflectorDown

public class DeflectorDown extends InstantCommand
{
    public DeflectorDown()
    {
        super();
        // Use requires() here to declare subsystem dependencies
        requires(Robot.deflector);
    }

    // Called once when the command executes
    protected void initialize()
    {
        Deflector.DEFLECTOR_SOLENOID.set(DoubleSolenoid.Value.kReverse);
    }
}