Radio control is controlling vehicles by radio wave signals. It is often used for making models of cars, boats, helicopters and airplanes move on their own like real ones. For controlling models, an operator uses a transmitter that has the model's controls on it. When a control is moved, the radio signal changes. The part on the model that takes the changing signals and helps turn them into movement is called the receiver. The receiver then tells a special kind of motor called a servo to move part of the model.