Over the weekend of 10-11 August 2002, the Carlisle & District 0 Gauge Group (CDOGG) manned the Guild Stand at our local railway exhibition. As part of our attempts to bring 0 gauge to a wider audience, we brought part of our test track and, as we have not yet wired the track, several radio-controlled locomotives. The interest shown was exceptional and many people went away convinced of the practicality of the system and its advantages. It seems appropriate to try and answer the questions asked at the show for a wider audience.

What are the advantages of radio control?

We are fortunate in having in our group Fleetwood Shawe, one of the pioneers of squeezing radio control into 7mm scale locomotives, and his early efforts paved the way for the rest of us. Fleetwood’s garden railway, 18 scale miles long, has proved the system beyond doubt. There is no need for complicated section switches and track wiring, track cleaning is abolished with the exception of removal of foreign bodies, and you can have true multi-locomotive working without DCC.

What are the disadvantages of radio control?

The addition of RC adds to the cost of the loco.

How do I go about it?

What we intend to do is to describe the components needed and give some suggestions on how to go about installing them in a 7mm loco. It is not a treatise on the working of radio control systems – there is already plenty of published material on this for those of you who are interested.

How does the radio control system work?

A transmitter (Tx) sends out a radio signal to a receiver (Rx). The signal is detected by the receiver which then sends a control signal to the servo or speed controller. Changing the position of the control levers or ‘sticks’ on the Tx alters the signal, which results in corresponding change at the Rx and servo or speed controller.

What is a servo?

A servo is a small electric motor with associated electronics to make it turn a required amount and then stop in response to the instructions from the Tx. Servos are not often used in battery powered 7mm locos but have an application in live steam engines.

What is a speed controller?

A speed controller is an electronic device which responds to a signal from the Tx (via the Rx) to change the speed and direction of the locomotive. Simple speed controllers can be made with resistance wire but they tend to be somewhat insensitive and bulky, so we are not going to consider their use in this application.

What’s all this frequency business?

The very much simplified physics bit! A radio wave is produced by an electric current oscillating in a circuit. The rate at which the current oscillates controls the frequency of the radio waves produced. An oscillation of 1 cycle per second is referred to as a frequency of 1 hertz (Hz). Mains electricity supply oscillates at 50 Hz, which accounts for the buzz that you sometimes get from TV and radio receivers. The use of radio frequencies is
controlled by the relevant authorities, which have allocated a number of frequencies for use by modellers. Three frequency bands are commonly used in this country. 27 MHz (27 megahertz or 27 million cycles per second), 35 MHz and 40 MHz. Within each of these bands are a number of ‘spot’ frequencies. To prevent interference between models a set of crystals (xtals) for each spot frequency is used in the Tx and Rx to make sure each receiver and transmitter combination (combo) affects only the model it should. Care should be taken to check that you are operating on a different spot frequency from others.

Which frequency is best?

35 MHz is allocated to model aircraft only, so must not be used for surface operation. 27 MHz can be used for both surface and aircraft, and 40 MHz can only be used for surface operation. So for our purposes we have the option of using either 27 MHz or 40 MHz.

What is the difference between AM and FM ?

AM stands for amplitude modulation and FM stands for frequency modulation, just like your radio at home. They are different methods of controlling the signal. AM sets are cheaper and slightly more prone to interference, while FM sets cost more but are less likely to suffer from interference.

Talking of interference, how do you stop one Tx affecting another loco?

For each band there are a number of plug in crystals that oscillate at a very precise frequency. These crystals are supplied in matched pairs, one for the Tx and one for the Rx. So to run a number of locos, you simply use different crystals in each system.

Ok, I’m interested; what frequency do I go for?

There is no simple answer to this; 27 MHz is commonly used for toys and these toys often have a fairly crude system so can produce a strong risk of interference. 40 MHz AM is less common so probably runs less of a risk of interference; 40 MHz FM sets are the best but do cost more.

How much does it cost?

Again this is a difficult question to answer exactly and we can only give a general guide. A 27 or 40 MHz AM two-channel set containing Tx, Rx, crystals, two servos, switch harness and battery box will cost in the region of £50. You can buy just the Tx and Rx combo but check you are also getting crystals. It’s a bit like buying a train set; the set is cheaper than buying the parts separately. A 40 MHz FM 6 channel set containing Tx, Rx, xtals, four servos, switch harness, Tx rechargeable battery, Rx rechargeable battery and charger will cost in the region of £125 to £150. Speed controllers are discussed later. You then need drive batteries; depending on the size and capacity these could range between £15 and £30.

Ask your local model shop about local aircraft, car and boat clubs, as it may be possible to contact members of these clubs and sell on the unwanted servos etc.

What kind of locomotives can have RC installed?

Almost any 7mm loco can have RC installed if it is planned from the start.

Can I use the existing motor?

Motors vary in efficiency and current demand. If building-in RC from the start, we would advise use of a 6V motor and gearbox. This allows you to use fewer cells, which makes installation easier. It is possible to fit RC retrospectively, and the availability of modern rechargeable cells makes it perfectly feasible to use the existing motor.

Can RC locos still be used on two-rail systems?

Yes. If you wish to retain the ability to run on two-rail, then a switch must be installed to allow the pick-ups to be isolated. Otherwise you will feed current to the rails or current from the rails, which could damage the speed controller and other equipment. Remember that some plunger-type pick-ups can produce a fair amount of drag; with track pick-up the extra power is easily provided by the controller, but keeping some types of pick-up on an RC loco could reduce the operational duration considerably. Nevertheless, it is perfectly feasible to use both types on the same track and we do this with no problems whatsoever. If you build your loco without pick-ups, you must still take care that you are isolated from the rails, as putting a loco that shorts out the track on a two-rail railway is not to be recommended!

Are RC and DCC compatible?

We have no experience of DCC, but if your RC loco is unable to pick up track power there should not be a problem. Any advice on this area would be appreciated.

Which make of RC is the best?

They all are. Modern RC equipment is reliable; people have their own favourite brand but one make is no better than the other. RC equipment has never been as affordable as it is today and your local model shop that caters for boats and aircraft will be able to advise.

What type of speed controller should I buy?

Again this is a matter of choice and available funds. Our group has experience of three makes, Antenna, Brian Jones and Mtroniks.

Mtroniks produces a range of controllers; these are cheaper than the other two brands but we have found some problems when using them in some locos. Mtroniks is working on overcoming these problems and if you want a cheaper way into experimenting with RC the Mtroniks ‘eco’ or ‘loco’ controllers in a Lima plastic-bodied loco should work very well. The Brian Jones ‘Mac five’ and the Antenna controllers work very well but the ‘Mac five’ is larger than the Antenna.

All three have the facility to set the loco running and then switch off the transmitter; the loco will then continue to run at the preset speed, control being regained when the Tx is switched back on.

(Please note that we are not recommending any one controller over the others, this is a matter of personal choice, finance, space available etc and we would be happy to offer further advice).

I have a loco that I don’t want to alter, is there any way of adding RC without changing the loco?

RC equipment and batteries can be placed in a van attached to the loco and connected with jumper wire, but take note of possible problems via pick-ups as mentioned earlier.

A 12ton ventilated van or similar is quite adequate for this purpose.

What kind of batteries should I use?

It is possible to use dry batteries, but the initial saving in price is soon lost when you examine the running costs over a period of time. Rechargeable cells do cost more but work out to be far more cost effective. Probably the best available at a reasonable price are Nickel metal Hydride (Ni-MH), which come in at a fair price and have a high capacity.

Nickel Cadmium (Nicad) batteries are also commonly available. Go for the largest capacity you can fit to extend operation time.

NB – largest capacity doesn’t necessarily come with largest size, the figure to look for is the mAh (milliamp hour) rating. Theoretically a fully charged 1000mAh battery should produce 1000mA (1 amp) for an hour, which would give several hours use in a normal operating session. Some manufactures produce larger size batteries which are simply a ‘small’ battery in a big case. Which ever batteries you decide to use remember to use a suitable fuse immediately after the batteries to protect the system.

Where do the RC components go?

If possible try to get the batteries in the loco; many boilers are capable of taking the required number of cells and this puts the weight over the driving wheels. If this is not possible then the tender of your average 0-6-0 will take them. If you really can’t fit them in the loco, and you want to try out the idea before modifying the loco, then test the system by placing the batteries and control components in your train. A bogie wagon or a couple of opens will carry all you need.

We normally put the control gear in the tender of a tender loco, but it is quite possible to build everything into a tank loco by using the tanks and boiler space. It is essential to place the aerial correctly (see later).

Is it true that RC locomotives are not as powerful as two-rail?

The answer to this is an emphatic NO. Sometimes a poorly-running loco can be persuaded to run better by upping the controller setting; a loco like this may struggle if converted to battery power. The answer is to sort out the loco problem first.

John Rigg of our group has a Jubilee which will pull 19 bogie coaches with ease, and at the Carlisle Show was pulling a dead two-rail loco out of the way as easily if it was not attached (we had to stop the demo because we didn’t want to flatten the loco wheels).

Where do I place the aerial?

The aerial can be disguised in a number of ways. A metal cab roof can be used provided it is insulated from the model; if fitting a tender loco, then a brass plate hidden under a layer of coal can be used. In each case solder the wire to the brass. In some circumstances we have simply placed the aerial wire in a loose coil in the coal space.

This is an area for experiment but there are two situations to be avoided. Firstly, do not cut the aerial wire; second, do not wrap the wire round other components such as the receiver or controller.

What about charging the batteries?

There are several arrangements for doing this. The best is to have a double-pole changeover switch with centre off. This can be used to switch the batteries from driving the motor to a charging socket mounted on the loco or tender. Otherwise it is possible to arrange to disconnect the batteries and connect them to a charger using a connecting block. Remember, if charging NiCad or NiMh batteries, you need the correct type of charger.

In an article of this nature we cannot cover every last detail. Installation in a particular loco varies depending on the construction and space available, but if you have built the loco then fitting radio control should cause no problems.