Arduino motor shields are modular electronic boards designed to easily drive motors with an Arduino board. The motor shields have pinouts suitable for Arduino R3 pinout. Motor shields can be classified as stepper motor shields, DC motor shields and PWM shields which can be used to drive servo motors. Besides these there are shields that are designed to drive different types of motors alone.
Motor drivers are used because the voltage and current provided by Arduino pins are not high enough to drive a motor. Motor drivers are integrated circuits that transfer higher currents to motors from their output pins. Motor shields are designed in a way that the motor driver IC pins connect to suitable Arduino pins.
Motor shields also have the required circuits for motor driver ICs to work properly. Besides these some designers also add extra circuits for the shield to use serial communication protocols, so that they don’t have to keep Arduino pins busy. The shields designed this way are also very suitable for stacking with other shields.