In your robotInit instead of:
Code:
Joystick left = new Joystick(1);
Joystick right = new Joystick(2);
RobotDrive robot = new RobotDrive(1,2,3,4);
Replace it with:
Code:
left = new Joystick(1);
right = new Joystick(2);
robot = new RobotDrive(1,2,3,4);
You already created the object above so right here you just have to initialize it! Your IDE should've given you an error...