Servo Motor Control

Robots must be able to interact with the environment around them too. Many types of actuators are used in FRC robotics; one of them is the ​Servo Motor. A servo motor is a special type of motor that can rotate to a precise position, usually between 0 and 180 degrees. They come in a variety of sizes and strengths. You can connect a servo motor to any of the ​PWM ports on the !RoboRIO. Examine the PWM ports and identify which row of pins are ground (, +6V, and Signal (S). Make sure you connect them to the proper pins on the Servo motor: black or brown goes to Ground, red or orange goes to +6V, yellow/white/blue goes to Signal. You can read more about servo motors ​here

Create another program using the TimedRobot java template and name it ServoTest. Modify the generated code as follows:

• Add the following imports:

  import edu.wpi.first.wpilibj.XboxController;
  import edu.wpi.first.wpilibj.GenericHID.Hand;
  import edu.wpi.first.wpilibj.Servo;
  

• declare variable for the Xbox controller and ​servo motor in the Robot class

     private XboxController xbox; 
     private Servo servo;
  

• in robotInit() instantiate the controller and motor objects

    xbox = new XboxController(0); // Xbox controller on port 0
    servo = new Servo(1);         // Servo connected to PWM 1
  

• in teleopPeriodic() read the xbox controller and adjust the servo motor accordingly

    // Read xbox controller left joystick x axis
    // value returned is between -1.0 and 1.0
    double x = xbox.getX(Hand.kLeft); 
    // Servo motors are controlled on a scale of 0.0 to 1.0
    // so re-scale the X value to that range (-1.0->0, 0->0.5, 1.0->1.0)
    x = (x + 1.0) / 2;
    // Set servo motor position based on joystick
    servo.set(x); 
  

Connect a Servo motor to PWM port 1 on the roboRIO and run your program. You'll need to press the Enable button on the driver station to put the robot in Teleop mode so that teleopPeriodic() is called repeatedly.

• Extra credit: use buttons on the Xbox controller to set the servo to a specific position (e.g. 45-degrees, 90-degrees, 135-degrees).