Control engines! The Arduino Motor Shield allows your Arduino to drive DC and stepper motors, relays and magnets.
Arduino® Shield Motor Rev3 The Arduino Motor Shield is based on the L298 (datasheet), a dual full-bridge driver for driving inductive loads such as relays, magnets, DC and stepper motors. It allows you to drive two DC motors with your Arduino board and control the speed and direction of each independently. Among other things, you can also measure the motor current consumption of each motor. The shield is TinkerKit compatible, meaning you can quickly create projects by plugging TinkerKit modules onto the board.