A radio system is made up of three main components, namely a Transmitter (Tx), a Receiver (Rx) and servos (Sx).  The transmitter is the handset or controller, this sends a signal to the receiver in the model which in turn transforms the message into a command, this is sent to the servos via a wire linkage and the desired movement is carried out.  Modern radios operate with proportional control.  This means that the servo will move proportionally to the transmitter stick.  This sort of control gives the model a more realistic feel and allow greater accuracy of movement.

THE TRANSMITTER (Tx)

The transmitters usually have two control sticks which govern the main functions of a model such as steering and throttle, elevator and aileron.  Alternatively, for some cars and boats a steerwheel set can be used.  These use the same principles but the sticks are replaced by a steering wheel and trigger.  The number of channels a radio set has refers to the number of things it can control simultaneously, a car for example would require a two channel set, one channel to control steering and one to control throttle.  Transmitters can now be bought with up to ten channels.  This facility is often used by marine modellers for water pumps, lights, winches and so forth.  Here is an example of how multiple channels might be used

Basic controls for helicopter sets are slightly different.  For example the rudder channel is used for tail rotor control, the aileron channel controls left/right cyclic and the elevator channel is used for fore/aft cyclic.

THE RECEIVER (Rx)
Receivers come in many different shapes, sizes and channel configurations to suit all applications.  Traditionally a two channel receiver could only be used with a two channel transmitter a 4ch Rx with a 4ch Tx, etc.  Modern receivers offer more compatibility and most receivers will work with most transmitters regardless of how many channels each operate, as long as the frequency bands are the same.  This makes it possible to fly a small two channel model with a two channel receiver (to keep the weight down), using a 6 channel transmitter.  This also means that you can have many different models and receivers all controlled by one handset.
SERVOS (Sx)
The servo is the part of the radio system that does the physical work.  Each transmitter channel requires one servo to function.  For example, to use all of the channels on a six channel transmitter you will need six servos. They come in many different shapes and sizes and vary vastly with regards to speed and power output.   This can make choosing the right servo for your desired application very difficult.   There needs to be the right balance between speed and torque.  A high speed servo may work well with a light load, but the test comes when it is used in the intended operation.  It the servo does not have the pull required then it will not move at the required speed.
BATTERIES
Radio sets are all battery powered, be it by drycell or Ni-Cad batteries.   Transmitters generally require 8 cells (9.6v), whilst the receiver can be powered by as little as 4 cells (4.8).  Most of the basic sets are sold in the drycell format, however in the long run it is more economical and practical to use rechargeable batteries.  Ni-Cads can be purchased as single cells or sealed packs.   Individual cells are less expensive but not highly recommended whilst there will always be doubts about the efficiency of the battery connections.  This is an unnecessary worry when pre-assembled Ni-Cad packs are available to suit most of the radio systems.  If you cannot find a pack to fit then ask us and we will make one to your own specifications.
FREQUENCY BANDS & CHANNELS
R/C Systems have their own frequency bands which very from country to country and change depending upon the type of modelling you are participating in.  In the UK the bands are 27MHz AM for general use, 35MHz FM for airborne models and 40MHz FM & AM for surface models.  It is important to ensure that the equipment you purchase operates on the correct frequency band for its intended application.  It is, for example, illegal to operate a model car on 35MHz.  It is also illegal to operate (in the UK) on any other frequencies than those listed here. In order to operate multiple models at the same time, each band is broken down into separate frequencies which we call channels.  Each channel is given a number or a colour.  There are 26 individual frequency steps on 35MHz which mean there are 26 different channels on this band (ch 60 to ch 95), 30 channels on 40 MHz (ch 66 to ch 95) and twelve different colour channels on 27MHz.
CRYSTALS (XTAL)
Crystals are the lifeline between the transmitter and the receiver.  In order to operate on different channels each Tx and Rx is fitted with a removable crystal.   Both crystals can be changed, allowing you to operate on number of different frequencies.  Crystals are generally marked with the channel number, the actual frequency and the letters Tx or Rx to designate the crystals use.  It is important to ensure that the Tx is fitted into the transmitter and the Rx into the receiver.  If you get it wrong it will often still operate in close proximity, but the problems will come when the model is a distance away.  Look after your crystals, if you drop them or crash your model then change them.  They are very fragile and easily broken.   Remember that radio signal problems rarely show up until the model is a distance away and it is too late.  Crystals can be bought as either single or dual conversion.   Dual conversion offers a number of advantages over single, namely an ability to filter out unwanted interference and problems with high power broadcast transmissions in the VHF band.  Dual crystals, however will only work with dual conversion receivers.   They are the same price and are instantly recognisable by an orange band on the tag.  The transmitter crystal remains the same.
MODULES
It is possible for some R/C systems to change their frequency band by changing the module, receiver and crystals.  This is ideal for converting systems intended for flying to surface use and is exceptionally useful when travelling abroad.
CONTROL TRANSMISSION - AM, FM or PCM
The control transmission and reception by an R/C system can take two different formats - AM (Amplitude Modulation) or FM (Frequency Modulation).  These are just two different ways that a signal can be transmitted.   AM switches the signal on and off at different speeds to dictate the position of the servo.  FM minutely adjusts the frequency to move the servo.  In the case of PCM (Pulse Code Modulation), the most advanced form of signal transmission, the signal is transmitted using FM as a base but it is also combined with a digitally coded signal, giving the precise position the servo is to move to.  PCM is not only extremely accurate, it also has other advantages, such as Failsafe or Hold functions and is widely used by most of the professionals in the industry.
TECHNICAL FEATURES
SERVO REVERSERS (Rev)
Servo Reversers are small switches on the transmitter which allow the direction of the servo rotation to be reversed.  This means that the servo control linkages can be installed in the best positions without having to worry if the servo is in the right sense.
TRIMS
Trims are the small sliders on the transmitter located beneath and to the side of the main control sticks.  These functions allow small alterations to be made to the main controls during the models operation.   Adjustments to control linkages can be made later on and the trims set back to neutral on the transmitter.  Trims can also be used to compensate for different power settings such as during landing.  Futaba have recently developed digital electronic trims which allow very precise amounts of trim to be applied step by step.
DUAL RATES (D/R)
Dual Rates allow the modeller to change the response setting for the controls at the flick of a switch.  Aileron and elevator are the most common uses for this function whilst it can be used to desensitise responsive models or alter the setting for larger models which will require more response when flying at slower speeds.  It works by pre-setting a desired position on the servo using an adjustable potentiometer, then when the dual rates are activated the servo travel will restricted to your desired setting.
ATVs
Adjustable Travel Volume, also referred to as end-point adjustment enables the maximum travel of the servos to be set in either direction, in relation to the full movement of the control stick on the tx.  This feature is commonly used to set up the throttle.
ATL
Adjustable Throttle Limiter can be found on many sports and computer radios.  It allows the effect of the throttle trim to only operate when the throttle stick is lower than its mid position.  Consequently, at full power the trim has no effect on the servo throw, making set-up and adjustment easy.
TRAINER SYSTEM
A Trainer System, also known as a buddy box system, connects two transmitters using a trainer lead.  This allows an instructor (or more experienced fellow pilot), who will have the main controls with the master transmitter (which will be switched on and transmitting a signal), to pass control to the student (who will be using the second transmitter) by activating a spring loaded toggle switch.  If the pilot with the master transmitter feels that the student is in trouble, control can instantly be regained by releasing the switch.  This is probably the best and safest way to learn to fly aircraft.
MIXING
Mixing is a feature of many radio systems whereby two functions or channels are combined electronically at the transmitter by using a rotary knot or in the program of a computer radio.  This  enables them both to move when only one control is moved.  Common aeroplane uses are for large scale aircraft which need combined aileron and rudder to turn smoothly, or combined elevator and flap for highly responsive aerobatic models.  Helicopter pilots generally mix throttle and pitch.
SNAP ROLL (SPIN) SWITCH
Snap roll is normally only available on computer radio systems where the direction can be changed in flight.  The activation of this function causes the model to roll or spin in a given direction.  All of the different control inputs required can be programmed into the transmitter before taking off.

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