Introduction to Radio Gear
by Roger Harper
                         
Page 2 of 4

Generally you will get just about everything you need when you purchase your radio system. As an example, most aircraft and helicopter systems (of four or more channels) come with transmitter, receiver, three or more servos, rechargeable NiCad batteries for both the transmitter and receiver, battery charger, switch harness, servo trays, aileron extension, frequency flag and extra servo control arms. I mention this because these account for the bulk of the systems on the market today.  Next comes the surface radio systems.  Some surface radio systems do not usually come with batteries or charger and only have two servos.  For a given radio system, there are usually several different packages available, each for an intended purpose.

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.

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.

Types of Radio Modulation — When shopping for a radio, you will find that people refer to different types of modulation. They are referring to the way the electronic control information is sent from your transmitter to the receiver over radio waves.  The types being AM, FM and PCM.

The following is a list of other functions and features which may be available on various radio systems.  Most of these are for aircraft radios, but I have included them because you may need this information later.  Plus, it's good reading.

Servo Reversing — This feature allows the modeler to reverse a servo's rotation direction at the flip of a switch. Servos can be mounted in the most convenient way without concern for their rotation direction. The proper movement can then be selected when the installation is completed.

Dual Rates (D/R) — Dual Rate allows the modeler to choose between two different control sensitivities. With the dual rate switch in the "OFF" position, 100% servo throw is available for maximum control response. In some more sophisticated systems this "OFF" position may be adjusted to provide anywhere from 30% to 120% of normal full throw. In the "ON" position, servo throw is reduced and the control response is effectively desensitized. The amount of throw in the Dual Rate "ON" position is usually adjustable from 30% to 100% of total servo movement. The modeler can tailor the sensitivity of his model to his own preferences.

Exponential Rate — Exponential Rate is where the servo movement is not directly proportional to the amount of control stick movement. Over the first half of the stick travel, the servo moves less than the stick. this makes control response milder and smoothes out level flight and normal flight maneuvers. Over the extreme half of the stick travel, the servo gradually catches up with the stick throw, achieving 100% servo travel at full stick throw for aerobatics or trouble situations.

Variable Trace Rate (VTR) — This radio function is similar to exponential except it uses two linear responses to determine the servo sensitivity on the first and second half of the control stick movements.

Fail Safe (FS) — An Electronically programmed mechanism in most PCM radios which automatically returns a servo or servos to neutral or a preset position in case of radio malfunction or interference.

Adjustable Travel Volume (ATV) — Frequently referred to as End Point Adjustment, ATV lets you independently preset the maximum travel of a servo either side of neutral.

Sub Trim — A radio function which allows very precise electronic centering of servos.

Direct Servo Controller (DSC) — Allows full function of an aircraft's servos via an umbilical cord. This permits adjustment of radio functions without switching on the RF portion of a transmitter.

Programmable Mixing — Electronic coupling of one channel to another. This one control input will yield output to two different servos.

Aileron/Rudder Mixing — Adds rudder control when aileron is input from the transmitter aileron stick.

V-Tail Mixing — Used when there is a V-Tail on the aircraft rather than the conventional elevator and rudder. Each control surface of the V is connected to a separate servo. Operating the elevator control stick will move both surfaces up for back stick or both surfaces down for forward stick. Moving the rudder control stick left will move the left surface of the V down and the right surface up. Moving the rudder control stick to the right will move the left surface of the V up and the right surface down.

Flaperon Mixing — Mixes the Flap and Aileron functions so that when each aileron is connected to a separate servo (one servo plugged into the aileron channel and the other plugged into the flap channel), the surfaces will act as both ailerons and flaps, depending on the position of the controls.

Elevon Mixing — Mixes the Elevator and Aileron functions, especially useful for delta-wing models where the elevator and ailerons are the same control surfaces. Each surface is connected to a separate servo (one servo plugged into the aileron channel and the other plugged into the elevator channel), the surfaces will act as both ailerons and elevator, depending on the position of the controls.

Flap/Elevator Mixing — Couples the Flaps and Elevators such that when the flaps are lowered, the elevator will be automatically adjusted to prevent pitching of the model.

Elevator/Flap Mixing — Couples the Elevators and Flaps such that when control is input to the elevators, the flaps will move in the opposite direction. This permits the model to perform tighter maneuvers in the pitch attitude.

Crow Mixing — Primarily used in gliders for spoiler action by mixing the flaps and ailerons. It is necessary for the ailerons to be using separate servos, plugged into separate channels and the flap servo to be independent of both aileron channels. Upon applying Crow Mixing, the flaps go down while both ailerons go up.

Differential Ailerons — This type of mixing is accomplished by having separate servos on each aileron, plugging one into the aileron channel and the other into another unused channel. The two channels can be programmed to both operate from the aileron control stick, however the travel volume for each aileron may be adjusted separately giving more deflection in one direction (usually up) than in the other.

Mode I — The control stick configuration with the rudder and elevator being controlled by the left stick while the right stick controls the throttle and ailerons.

Mode II — The control stick configuration with the ailerons and elevator being controlled by the right stick while the left stick controls the rudder and throttle.

Mode III — The control stick configuration with the rudder and elevator being controlled by the right stick while the left stick controls the ailerons and throttle.

Dual Conversion — Dual Conversion refers to the method in which the receiver processes the incoming signal. Generally a Dual Conversion receiver is less prone to outside interference and is the preferred type of receiver.

Trainer System — The trainer system feature allows two transmitters of similar design to be connected together via a cord (trainer cord) so that one transmitter may be used by an instructor and the second one by a student when teaching to fly. The instructor simply has to hold a switch on his transmitter to give the student's transmitter full control. If the student gets into trouble, the instructor can release the switch and he has full control of the model.

Snap Roll Button — This feature is found on more complex radios and is used to perform a snap roll maneuver by simply pressing one button. The function is usually programmable to give a combination of rudder, elevator and aileron control.