Joysticks and Game Controllers

This tutorial shows how to map keys on a game controller to commands that will be run on the robot. On the competition robot you'll be using two game controllers one for the driver and the other for the operator. Each controller will map to a set of commands that are appropriate for the robot driver and operator. The mapping is determined by the nature of the competition game rules and how tasks are divided between the driver and operator. Some commands will be duplicated on both controllers.

It can become difficult to keep track of this key mapping, especially as more commands are added, so there needs to be a good way of organizing them.

The DriverOI Class

The DriverOI class is used to accept Operator Input from game controllers. It's main purpose is to map keys on the game controller to function names that describe the operation that's to be performed. It somewhat follows a functional programming paradigm which describes what the function is doing rather than how to do it.

Lab - Joysticks and Game Controllers

There's one task for the lab:

  • Create the OperatorOI class to map keys to the commands that will be initiated from the operator's game controller.

Create the OperatorOI Class

Create a new empty class from the files panel in VSCode. Right mouse-click on the oi folder and select "Create a new class/command". Select "Empty Class" from the dropdown and enter OperatorOI for the name of your new class.

This class will be using the XboxController, so inside of the curly braces create a member variable for it:

    private XboxController m_controller;

Every class needs a constructor so create one for this class. It must have the same name as the class. Capture the XboxController and assign it to the method variable.

public OperatorOI(XboxController controller) {
    m_controller = controller;
}

Create two buttons to shift the transmission gears. The methods that return the buttons should be descriptive of the function that they will perform, such as getShiftLowButton(). When prompted to import the Button class make sure that you select the edu.wpi.first.wpilibj2.command.button.Button. The buttons will be assigned to the X and Y buttons of the game controller.

public Button getShiftLowButton() {
    return new JoystickButton(m_controller, XboxController.Button.kX.value);
}

public Button getShiftHighButton() {
    return new JoystickButton(m_controller, XboxController.Button.kY.value);
}

You should now have a functional OperatorOI class. To test it you'll need to add it to the RobotContainer. In the RobotContainer class create a new method variable called m_operatorController of type XboxController that will get assigned to the operators game controller. Assign it to port 1 since the driver's controller is already assigned to port 0. 

private final XboxController m_operatorController = new XboxController(1);

Create a method variable called m_operatorOI and assign the new m_operatorController to it.

private final OperatorOI m_operatorOI = new OperatorOI(m_operatorController);

In the configureDrivetrain() method add the button commands to shift the Transmission gears.

m_operatorOI.getShiftLowButton().whenPressed(new InstantCommand(m_transmission::setLow, m_transmission));
m_operatorOI.getShiftHighButton().whenPressed(new InstantCommand(m_transmission::setHigh, m_transmission));

Testing the OperatorOI Class

Start the DriveStation application and connect to the roboRIO robot.

Plug two game controllers into the laptop and view the USB Devices Tab to ensure that the driver's controller is assigned to port 0 and the operator's controller is assigned to port 1.

Test that both the driver's and operator's controller can change the Transmission gears.

You're now done with this task!

References