Servos are awesome for controlling a RC car or robot. Inside each one is a DC brushless motor, some gearing, electronics, and a potentiometer. What does all that mean to you?
You tell them where to go by sending a Power Width Modulation (PWM) signal. The Arduino UNO R3, for example, can send 6 PWM signals at once. The MEGA has a crazy number of PWM signals.
The gear sticking out the top is 5.5mm in diameter
Range: 180 degrees