# Lesson 2: How to Create Commands

Teachers will guide students through the process of creating and managing Commands in the Command-Based WPILib structure for XRP. Students will learn how to design modular robot actions.

• Completion of Lesson 1: Set Up and Move the Robot.
• Students understand how subsystems interact with commands.
• XRP and VS Code are set up and connected.

This lesson teaches students how to use the command-based model to separate logic cleanly. The focus is understanding the lifecycle of commands and why modular design matters in FRC programming.

Explain the key phases of a Command:

• initialize() — Runs once when command starts.
• execute() — Runs repeatedly while active.
• end() — Runs once when finished or interrupted.
• isFinished() — Determines when command ends.

Illustrate this lifecycle with a diagram on the board.

package frc.robot.commands;

import edu.wpi.first.wpilibj2.command.Command;
import frc.robot.subsystems.XRPDrivetrain;
import edu.wpi.first.wpilibj.Timer;

public class DriveTime extends Command {
    private final XRPDrivetrain drive;
    private final double speed;
    private final double duration;
    private final Timer timer = new Timer();

    public DriveTime(XRPDrivetrain subsystem, double speed, double duration) {
        this.drive = subsystem;
        this.speed = speed;
        this.duration = duration;
        addRequirements(drive);
    }

    @Override
    public void initialize() {
        timer.reset();
        timer.start();
    }

    @Override
    public void execute() {
        drive.arcadeDrive(speed, 0);
    }

    @Override
    public void end(boolean interrupted) {
        drive.arcadeDrive(0, 0);
        timer.stop();
    }

    @Override
    public boolean isFinished() {
        return timer.hasElapsed(duration);
    }
}

Add a test binding to RobotContainer.java:

public class RobotContainer {
    private final XRPDrivetrain m_xrpDrivetrain = new XRPDrivetrain();

    private final CommandXboxController controller = new CommandXboxController(0);

    private final DriveTime driveTime = new DriveTime(m_xrpDrivetrain, 0.8, 2);

    public RobotContainer() {
        configureBindings();
    }

    private void configureBindings() {
        controller.b().onTrue(driveTime);
    }
}

• Have students experiment with different speeds and durations.
• Explain how the addRequirements() method prevents hardware conflicts.
• Show how Commands can be composed into autonomous routines later.

• Write a TurnTime command that spins in place.
• Combine commands into a SequentialCommandGroup.
• Challenge students to create a simple autonomous routine.

45 minutes (concept introduction + coding)

• Understand how Commands encapsulate robot actions.
• Learn to use initialize, execute, end, and isFinished methods.
• Be able to create and trigger Commands via joystick input.