#### Event triggered when a button is pressed
onevent buttons
    # Button forward is pressed, so increase speed
    when button.forward == 1 do 
        speed += 50
        call math.min(speed, speed, 500)
    end
    # Button backward is pressed, so decrease speed
    when button.backward == 1 do 
        speed -= 50
        call math.max(speed, speed, -300)
    end
    # Button center is pressed, so stop the robot
    when button.center == 1 do
        speed = 0
        motor.left.target = 0
        motor.right.target = 0
    end