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The Basic Radio System
 
Author: Howard Sullivan

The Basic Radio System
(reproduced with permission of Howard Sullivan)
There are many modern radio systems from which the beginner can choose. There are several common brands including Futaba, Airtronics, JR, Hitec, and Ace. Each of these offers a wide range of options from a simple 2 - channel to a computer assisted 8 - channel system. The buyer is limited only by his budget. A beginner should discuss his choice of systems with his intended instructor. There are several reasons for doing this, the primary reason being that the student's systems must be compatible with the instructor's system if it will be used as a buddy box. This issue will be covered in more detail later.

All basic radio systems consist of four (4) basic components.
Transmitter - The unit which takes the input from the user through the gimbals or sticks, encodes it, and sends it to the aircraft
Receiver - The unit that receives the signal, decodes it, and routes it to the appropriate servo
Servos - The device that converts the decoded signal to mechanical force to operate a control surface
Batteries - The device that provides power for the other devices to operate

There are specific frequencies assigned by the Federal Communications Commission (FCC) for use with airborne R/C models. A beginner must ensure that the system that he chooses is tuned to one of these frequencies. Most radio system manufacturers place a sticker on the outside of the carton that says, For airborne use only. There is a frequency reference chart available that lists the purposes of all of the frequencies that are assigned for R/C use.
The radio that is chosen must meet the 1991 specifications for narrow band receivers. The actual requirements of these specifications need not be known by the beginner because the systems are required to be certified to this standard. The owner's manual for the system will note that the requirements are met and many of the transmitters and receivers will have a gold sticker to signify this fact.
The radio system may transmit and receive on either an AM frequency or an FM frequency. The FM frequencies are less prone to interference than the AM frequencies although those using AM frequencies seldom have problems with interference. Some radio systems use one of two types of internal systems to help to nullify interference. These are called PPM and PCM. Each has its advantage but they are only available in more expensive radio systems and should not concern the beginner.

(see Typical Radio System diagram)

Regardless of the brand of system, the number of channels, or the price, all transmitters have the same basic components. Transmitters may have additional switches, slides, and displays depending on the functions they perform but the basic components remain the same.

Antenna The telescoping tube that transmits the signal
Batteries The device that provides power to the transmitter
Battery Meter The device used to monitor the strength of the transmitter batteries
Crystal The device that sets the radio frequency of the transmission
Gimbal or Stick The device that allows the user to input desired control movements into the transmitter
Handle The device for carrying the transmitter
Trainer Switch The switch used to allow an instructor to give control of a model to a student
Trim Lever Slides used to adjust control surfaces during flight

There are two primary modes of operation, meaning the way the gimbals are set up for operation. There are unsettled debates as to which mode is the easiest to use and best for a beginner. The modes of operation have become switched between the United States and most European countries. Mode I is primarily used in Europe while Mode II is used in the United States.

(See Mode I diagram)

Mode I started in the days of reed actuated proportional systems. The transmitters were uniformly set up in this manner. The thought was that the elevator and rudder or ailerons were the primary controls and each should be operated by an opposite hand for precision control Later this carried over into the more modern proportional systems since this was the mode used by most modelers.

(See Mode II diagram)

In later years, the thinking changed to the Mode II configuration. More modelers believed that it was easier to control the primary surfaces effectively with the same hand. Mode II grew in popularity and is used almost exclusively in the USA> A beginner does not have to be concerned about which mode he should select since most manufacturers install the gimbals according the most widelly used mode for the nation to which the radio system is being shipped.

There have been discussions over the years involving the number of channels with which a beginner should start. Some people say that only three channels should be used; rudder, elevator and throttle. The argument here is that it is easier for a beginner to only be concerned with using the rudder to make turns and not be concerned with the ailerons. Others contend that four channels should be used; rudder, ailerons, elevator, and throttle. The contention in this argument is that by not using ailerons, a beginner must go through a second phase of beginner training that being learning how to use ailerons. A four channel system offers better control of the model during takeoffs and landings in cross wind conditions. If a beginner chooses to use only three channels, he can set up the trainer so that the ailerons are not used initially and then add them later. The four channel approach to training is more widely accepted today.

A beginner might consider buying one of the more advanced six channel systems to get some of the features that are not available in the basic system such as dual rate controls. This feature allows the used to reduce the sensitivity of the sticks thereby reducing the chance of over controlling. If the beginner is relatively sure of future goals that involve the use of a six channel system, he can consider this an investment in his future and therefore save money. A lot must be determined before the initial purchase and should be discussed at length with experienced modelers, especially the intended instructor, before the purchase is made.

Effects of Control Surfaces
The new radio systems are proportional control meaning that the control surfaces move in proportion to the amount of movement of the stick. If the stick is moved half of its total travel in one direction, the corresponding control surface will move half of its total travel in the corresponding direction. A beginner must first know the effect that a stick movement has on the model. During normal flight, the throttle is set so that a constant speed is maintained. This means that thrust is equal to drag and lift is equal to weight. From this stable condition, the effects that the stick movements have on the trainer are described.

Right Stick - Pull Back (see diagram)
When the right stick is pulled back, the elevator moves up. This causes the ose to pitch upward increasing the angle of attack of the wing and increasing drag. If power is not applied, the airplane will slow down and eventually stall. This means that the air passing over the wing becomes turbulent and lift decreases until weight exceeds lift and the airplane will begin to drop.

Right Stick - Push Forward (see diagram)
When the right stick is pushed forward, the elevator moves down. This causes the nose to pitch downward reducing the angle of attack of the wing and reducing drag. As the airplane descends its speed increases until drag and thrust are again in balance.

Right Stick - Move Right (see diagram)
When the right stick is moved right, the left aileron moves down and the right aileron moves up. This causes the airplane to roll to the right meaning that the left wing moves up and the right wing moves down. It will continue to roll as long as the stick is held in the same position. When the roll takes place, lift is no longer oriented vertically so the effective lilft decreases. As the angle of the roll increases, effective lift continues to decrease and the airplane will begin to drop.

Right Stick - Move Left (see diagram)
When the right stick is moved left, the left aileron moves up and the right aileron moves down. This causes the airplane to roll to the left meaning that the right wing moves up and the left wing moves down. It will continue to roll as long as the stick is held in the same position. When the roll takes place, lift is no longer oriented vertically so the effective lift decreases. As the angle of the roll increases, effective lift continues to decrease and the airplane will begin to drop.

Left Stick - Move Right (see diagram)
When the left stick is moved right, the rudder moves to the right. This causes the airplane to swing or yaw to the right. This causes the left wing to move slightly faster through the air causing an increase in lift. The combination of the yaw and the lift increase on the left wing results in a gentle turn to the right as long as the stick is held in position.

Left Stick - Move Left (see diagram)
When the left stick is moved left, the rudder moves to the left. This causes the airplane to wing or yaw to the left. This causes the right wing to move slightly faster through the air causing an increase in lift. The combination of the yaw and the lift increase on the right wing results in a gentle turn to the left as long as the stick is held in position.

When the left stick is moved forward, the throttle is opened resulting in an increase in speed of the airplane. This causes an increase in lift and results in a tendency for the aircraft to climb. When the left stick is moved back, the throttle is closed resulting in a decrease in speed. This causes a decrease in lfit and results in a tendency for the aircraft to descend.

It is obvious from the descriptions of the effects of stick movement, that any movement can adversely affect the flight of a model. These effects can be overcome by using a combination of control surfaces to achieve the desired results. For instance, the right stick can be moved back when it is moved left. The result of this action would be that the nose of the airplane would be raised to overcome the loss of lift resulting in a banked turn without a loss of altitude.

In order to understand how to properly use the controls, a change in thinking may be required of a beginner who has some basic knowledge of control surfaces. A beginner must remember the forces acting on a model in flight and how they affect the model.

Copyright 1997-2002 Howard Sullivan







 

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Left stick - move left
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Left stick - move right
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Right stick - move left
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Right stick - move right
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Right Stick - Pull Back
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Right stick - push forward
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Transmitter Mode I
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Transmitter Mode II

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