The radio system is your link between you and your model. It allows the modeller to control his or her model. Radios can be separated into two groups, those used for model aircraft and those used for surface models. Although the operation, electronics, and mechanics for both types of systems are virtually identical, they operate on different sets of frequencies. The separation is stipulated by law and it is to protect the safety of the modeller and those in the vicinity. A flying aircraft can be dangerous if it becomes uncontrolled and the frequency separation helps avoid an aircraft being interfered with by someone operating a car or boat.
In addition to a difference in frequencies, some surface radios are also available with a pistol grip control which is ergonomically easier when controlling cars and boats. A pistol grip for aircraft would be impractical.
The first criteria one usually looks for when choosing a radio is the number of control functions or channels. (Note that the term channels here refers to the number of controls and does not have anything to do with the frequency on which the radio operates.) Generally modern radio systems are available with anything from 2 to 10 channels.
Car and Boat Radios
Radios used for surface models generally have from 2 to 4 channels with 2 channel units being the most popular. One channel would be for the steering of the model while the other would be for control of the speed and direction (forward or reverse) of the model. On a boat other channels can be used for operating lights, sirens etc. Pistol grip radios are quite often more comfortable in controlling surface models.
Gliders usually require 2 channels of control, one for rudder and one for elevator. Additional channels may be utilized for ailerons, flaps, spoilers, etc. on more sophisticated models.
Model aircraft may require anything from 2 to 8 or even 10 channels of control, depending on complexity. The average aircraft will generally require at least 4 channels of control, one for rudder, one for elevator, one for ailerons and one for throttle. Simpler models may omit the ailerons and some even the throttle (common with smaller 1/2A models). With no throttle in an aircraft, the model would be flown with full throttle until the fuel has run out. It would then be glided in for a landing without power. Additional radio channels may be used for things such as retractable landing gear, operating flaps, bomb drop, camera actuation, glider release, etc.
Model helicopters usually require different radios than model aircraft. Their controls are different with more mixing functions required. Usually a helicopter will operate with a minimum of 5 channels with the throttle and collective pitch channels both being controlled by one movement of the throttle control stick.
Components of a Radio System
Transmitter — The transmitter is the control box which you hold that converts your human control movements into electrical impulses and sends them via radio waves to the receiver in your model.
Receiver — The receiver is the small electronic unit in your model which converts the radio signal from your transmitter into electrical control signals which can be sent to your servos.
Servos — Servos are the devices in the model which actually produce the control movements. They convert the electrical signals from your receiver into physical movement to control your model. A different servo is required for each control function or radio channel. On larger models servos may be operated in pairs from a single channel to move control surfaces i.e one servo for each aileron.
Batteries — Two and three channel radio systems, for the most part, do not come with batteries and additional Alkaline (AA-type) cells are required. Again, these systems are generally used in surface vehicles. Virtually all 4 channel and greater systems come complete with NiCad rechargeable battery packs (for both transmitter and receiver) and charger.