Manual Robbe Futaba FX-40 (page 99 of 105) (English)

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Tips and notes

FX-40

20. TIPS ON INSTALLING THE RECEIVING SYSTEM

20.1 INSTALLING AND USING RECEIVERS

In the last few years the technical equipment carried in our

models has under

gone enormous changes. These include

brushless motors and contr

ollers, Lithium flight batteries, tele-

metry systems, GPS systems etc. etc., to mention just a few

broad categories.

At the same the materials used in our models have altered,

with the widespread introduction of carbon fibre into the

modelling world. More and more carbon parts, Lithium batte-

ries and brushless motors are now employed, with the aim of

producing strong, lightweight, high-performance models. In

model helicopters the toothed-belt drive system for the tail

rotor has virtually become standard.

At the design stage the installation of the servos, motor and

flight battery is generally laid down, but the receiver is often

left to last, and has to be squeezed into whatever space

remains. At the same time we all assume that the RC system

will provide completely reliable control of the final model /

power system configuration.

However, this is not a safe assumption on its own, as there are

vast numbers of possible combinations of metal, plastic and

carbon components, and many of them - especially in con-

junction with toothed-belt drive systems - can have a more or

less pronounced adverse effect on quality of reception. Com-

bining the various electrically conductive and non-conductive

materials can cause potential spark points where static char-

ges build up at the junction between different materials, and

these can have a massive effect on reception.

Although the receiver position is very important to reception

quality, it is not the only problem area: another crucial aspect

is the deployment of the aerial. Neither is it true that all recei-

vers are the same: small, slim, lightweight types are required

for some applications, whereas top priority for other types of

model is a large number of channels. The result is that the

range of receivers available commercially is extremely broad,

and every receiver type features its individual characteristics in

respect of sensitivity to the transmitter signal and rejection of

potential interference (electro-smog).

Reception quality is also affected by the number of servos in

the model, and the length and position of their cables. In some

aircraft large parts of the fuselage or fuselage reinforcements

are manufactured from conductive materials (carbon fibre, alu-

minium foil, metal), and these substances shield the transmit-

ter signal, resulting in a significant loss of reception quality.

The same applies to fuselages which are finished in heavily

pigmented or metallic paints.

Pushrods, carbon rovings and servo leads running parallel to

the receiver aerial affect the electrical field around the aerial,

and also tend to absorb the transmitter energy. This has the

overall effect of markedly reducing the energy of the transmit-

ter signal which the receiver aerial is able to exploit.

Even the weather has its part to play: in fine, dry weather con-

ditions air humidity is reduced, and this tends to produce more

electro-static charge in the model than in damp conditions. On

humid days, on the other hand, the ground reflects a greater

proportion of the transmitted energy. This can have the effect

of generating “reception dead-spots” - varying according to

the aerial angle and the distance to the model - because the

transmitted signals broadcast via the air and reflected from the

ground tend to cancel each other out or amplify each other

(timing differences of the two waves). Indoor flying - in sports

halls, for example - often takes place in buildings of steel or

steel-reinforced concrete construction, where multiple reflec-

tions (roof - floor - walls) can very often generate “reception

dead-spots”.

It is impossible for radio manufacturers to test out all these

combinations of models, materials, aerial angles, aerial posi-

tions etc., especially since the errors are cumulative: several

minor “imperfections” can add up, generating serious interfe-

rence. Only the individual modeller or model flyer can test and

eradicate these conditions for himself.

The following list contains a few elementary notes on

methods of obtaining optimum r

eception characteristics:

20.2 RECEIVER AERIAL:

The r

eceiver aerial is connec-

ted permanently to the r

ecei-

ver

. Never shorten or extend

the aerial. If possible deploy it

in an L-shape.

If this is not possible, we

recommend that you deploy

the aerial in an S-shape by

winding the wire onto a small

plate made of card, plywood

or plastic, as shown in the

sketch here, and locate it as

close to the receiver as possi-

ble. This does not reduce the receiver’s effective range.

Avoid aerial damage by fitting a tension relief and guide, e.g. a

short piece of fuel tubing, where the wire exits the fuselage. It

is essential to ensure that the aerial cannot foul the propeller.

It is also of fundamental importance to heed the following

points r

elating to r

eceiver aerial positioning:

• If possible deploy the aerial in an L-shape to avoid attitude-

dependent problems.

•

Do not deploy the aerial parallel to electrically conductive

materials, such as cables, metal “snakes”, control cables,

carbon pushrods etc., or along the inside or outside of elec-

trically conductive fuselages.

• Cables connected to the receiver (servos, batteries etc.)

should not be of the same length as the aerial, nor half its

length, nor whole-number multiples of it. For example:

receiver aerial length 1 m; avoid the following cable lengths:

0.5 m, 1 m, 2 m, 3 m etc.

• Keep the aerial as far away as possible from:

• High-current speed controller cables and motor cables;

• Sparkplugs and glowplugs, ignition units and onboard

glowplug energisers;

• Locations where static charges are likely to build up, such

as toothed belts, turbines etc.;

• If the fuselage is made of a material with shielding qualities,

run the aerial directly out of the fuselage;

• Do not attach the end of the aerial to an electrically conduc-

tive material (metal, carbon fibre);

• Whip aerials must never be attached to electrically conduc-

tive materials (carbon, aluminium etc.). High-speed models

are particularly susceptible to the build-up of static charges

due to high airspeeds. On such models the whip aerial must

not be attached to the surface of the fuselage.

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