How Do Digital Proportional Radio Control Systems Work?

By Isaiah David

Preliminaries

A radio-controlled model receives a lot of information. The transmitter for a simple RC car has to send constant updates to the receiver about how fast to go, and which way to turn. A plane has to receive even more information. The controller may seperately control each elevator, the rudder, the ailerons, the throttle, the wheels, and the flaps. Although it is possible to encode all of this information into a normal FM signal, Digital proportional radio control systems usually use what is called Pulse-Position Modulation, sometimes called pulse-code modulation, to create an accurate set of instructions for the vehicle.

The Transmitter And Receiver

Pulse position modulation is an elegant, simple way of encoding complex instructions. The receiver expects a pulse from the transmitter at certain intervals. The transmitter gives the receiver instructions by varying the timing of the pulse. By sending it slightly later or earlier than the expected time, the transmitter sends instructions to the receiver about what the RC car, boat, airplane, or whatever should do. A lot of information can be conveyed simply by varying the timing slightly.

The Servos

The receiver takes the signal and turns it into precise instructions for the servos, the small electric motors that control the RC vehicle. The signals the receiver gets are short pulses, but it sends out sustained electric current to the components. For example, If the wheels were turned all the way to the left on an RC car, and the transmitter told the receiver to turn them all the way to the right, the receiver will then keep sending power to the servos until it turns all the way.