Radio Installations - Part 1 (Setting up your Radio system)

OK, so you've bought youre model, built it and now you are ready to install your radio system in the model. Whether or not you have bought 2, 4, 6 or 8 channel radio. The set up will be near enough the same for all of these.

You should always start by planning your installation and where best to install your wiring and servos. The manufacturer of your particular model will have thought out the installations of your various pushrods and control snake runs for you as the model is built. This is essential for you as a begginer because it gives you an idea of what happens and where things go for future reference. These positions are worth noting for later when you may wish to build from plans etc. Which dont always show radio installation.

Probably one of the most common mistakes that people make is that they think the radio and pushrods can all be installed after the model has been finished so they leave it all till the end. This is when the discovery is made that you cannot get a control snake properly fixed inside a built fuselage. Mostly this will be obvious although the throttle snake is usually the worst to correct where you have three formers ahead of the wing leading edge and the middle one cannot be accessed for drilling.

Another common mistake is that due to poor planning of the setup there are too many tight curves in the snake causing it to bind in its outer sleeve. This will stress the servo and drain that all important flight battery very fast. All control runs must be as straight as is humanly possible.

Here you can see the snake is almost at right angles..

and here a smoother curve..

This is what we call the excess movement between servo and control surface linkage EG aileron. Usually caused by poorly fixed snakes and bell cranks or by badly fitting clevices and control horns. The best you can hope for in in this situation is poor response. At worst this can Cause flutter.
Control surface flutter is perhaps one of the more serious conditions that a model can develope. It will usually manifest itself in two forms to you. The first is a different feel to control inputs (not so obvious ). The second is an unusual buzzing noise particularly at high speed.
Flutter is so dangerous because the high vibration emitted can destroy large chunks of your airframe in no time at all. Leaving you with an unguided missile to play with.

You may or may not have read about keeping the joints between fin/rudder and wing/aileron to a bare minimum. well this can contribute to control surface flutter as well so small/no gap is the order of the day. It is so easy to achieve a close fit of surfaces that it isn't worth ignoring.
Secondly, Try and make sure that all of your connections e.g z-bends to control horns. Make sure that the hole in the horn is snug fit on the pushrod or clevice. This is also relevant to bell cranks.

If during a flight you detect the onset of surface flutter, only this action can save your model (unless you are very lucky).
SLOW DOWN !!! . It is safe to say that flutter occours at high speed. Close your throttle and enter a shallow climb (gently) dont attempt to yank the sticks in a panic youll only make things worse. As the model slows so will the flutter and when the aeroplane has recovered land, go home and fix the problem. Do not just assume that if you fly slowly for the rest of the day itll be allright. Check over the whole airframe for stress and damage.

Servo's, next to the flight battery are possibly the heaviest items in your radio pack. Now most conventional models by default need weight added to the nose to balance them correctly so to reduce the weight of the over all model they should be mounted as far forward as practically possible.
Also they should be arranged in such a manner that they dont interfere with each other at extremes of movement (see below.). They should be mounted on a firm but light base so that in operation they do not move instead of the surface being operated.

Here in the picture on the left you can see a typical servo installation in the fuselage of a model Trainer. these servo's are mounted on a plywood tray wich can be moved fore and aft to suit the correct cof g for the model. Once the best position has been achieved then the pushrods or snakes can be cut to the correct lengths and fitted to the servo's. Many manufacturers produce pre-formed trays in injection moulded plastic to save you from making up a ply tray. These are much lighter in weight and designed specifically for your particular radio system.

An alternative setup for aileron servo's

This is probably the most common setup in most models.

There Are very few hard and fast rules as far as the layout is concerened but these methods of have been accepted for many years as the most practical. However if you look at the picture (above right) you will see a poor example of a throttle linkage, the pushrod is bent at right angles. This although fairly unlikely give rise to flexing in the linkage and should be straight.

Pushrods are usualy made up of either a short threaded rod with a z-bend at the servo end or two threaded rods bound to a lenght of srpuce or dowel. These are normally installed to run the length of the fuselage instead of snakes. If correctly made they should taper at either end to prevent binding when side by side in smaller models. They are one of the preferred methods in larger models as they afford less flexing at either end than snakes can.
Snakes are made up from an inner core or cable running within an outer sleeve in much the same way as push bike brake cables. The closest relative bieng the Bowden cable.
Although perhaps more difficult to install, by far the best way of operating a control surface is to use the pull-pull or closed loop system. this offers the most reliable and accurate method of control and if done correctly can eliminate any chance of surface flutter (see pictures below for setup).

One srevo opertes a straight loop system and the other through a bell crank here.

Here you can see the other end of the system.

This setup is most common on glider rudders and large scale models because of its reliability. It is also regularly used in older full sized aircraft

Pushrod installation..

pushrod construction.

These clevices are regularly seen in many models kits purchased today. Do yourself a favour and throw all but one away. replace these with the metal kind even if you have to change the threaded rod as well. If you fly in very cold conditions and they become brittle, they can break very easily. At best they are in my opinion an accident waiting to happen. I would however use one on the throttle connection where the throttle arm on the engine is made of metal. A metal clevice here can cause interference of the radio as the two surfaces vibrate together when the engine is running.

In this picture on the right you can see a plastic clevice installed in such a situation. Here even if the clevice does break the concequences are less than disasterous but more of an inconvenience. If you must use these items then I would recommend a small piece of fuel tube slid over the jaws to keep the connection secure. It cannot be stressed enough that if one clevice fails on your model not only is it curtains for the model but also puts anyone nearby in danger. If a person is hit by a 4 lb model at 20 mph it can seriously injure or possibly even kill. On a lighter note there is one form of plastic clevice that is very safe and can be used on any surface with complete confidence. I am of course talking about the....

The only place for plastic clevices..

These wonderful little widgets are more common on helicopters and large models or where the control snake exits the fuselage at a steep angle.
They basically consist of a metal ball with an socket that snaps tight onto it. The ball is connected to the control horn with a nut and bolt. This system can withstrand some very high stresses and can be fitted almost any where.

Next Part I will be looking at Receivers and Batteries

Article by Grot from Bumpy Green Model Aerodrome
10th September 2001