7mm:1ft - 0 Gauge Railway Modelling.

By Raymond Walley
Manufactured by: Exactoscale (No longer available from this source.)
However, the original manufacturer is:  http://www.redarrowcontrol.co.uk/
 

The Red Arrow System. - Introduction

I have always disliked the idea of using electrified tracks to power locomotives, unless of course one is modelling a prototype that used them.  On conventional layouts that run well all the rails, whether main running lines or back sidings, shine with an effulgence quite out of keeping with reality.  Added to which it is a real chore to keep cleaning track work as well as being potentially dangerous to delicate line side features.

 

Not to mention the miles of wire, electronic gubbins and associated knowledge required. This is in addition to the potential problems with pickups, dirt and friction. It also takes up time that can be better spent on building engines and stock and track work.

 

From this you will understand that I am not keen on the method.  Also, modern low current motors run better on pure DC so they are perfect for battery operation, if we can pack enough power into the space available. Therefore, I have always been interested in making use of other control methods that would obviate using smoothed AC through the rails.

 

An advantage of taking such a route means that engines will have to be "driven" correctly and due observance given to signals. No cheating by cutting off the power if a signal is overrun for example, another plus toward achieving realism.

 

Ultimately, live steam is the one true method, coal fired of course for the realism in smells and sounds but I have only seen this in Gauge 1 and upwards and the method is not really practicable for most indoor uses in 7mm.  More to the point perhaps, it also requires a level of engineering skill and machine tools (or access to large quantities of money!) I do not yet possess.

 

I have tried radio control with reasonable results so far in small locomotives. However, when I came across a method at the Reading show some years ago using infra red signals to control battery powered locomotives I decided to invest in enough of the equipment to try it out and see if it was a practical proposition for small engines.

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The chosen locomotive was a GWR 0-4-2 No: 848, which I had already built and had painted for me from one of Malcolm Mitchell's 517 kits. This is the engine that I had also used to experiment with radio control too. Ideally I suppose, one should decide upon the control and propulsion system before construction commences but I consider that any viable method of control - aside from steam - should be capable of retrofitting.

 

One important point. It is vital that the chassis is free running. This is not usually a problem with carefully constructed engines that are well designed in the first place.  Modern low voltage motors with integral gear boxes generally draw a very low current - in the order of 0.25 amps - but stiff motion, gears or wheel sets will cause a much higher current drain than necessary and negate the benefits by drastically shortening running time and possibly causing overheating of the transistors of the control module.

 

It may even threaten the life of the motor and or electronic components in the receiver. The system is called "Red Arrow" and is was by Exactoscale of Esher (usual disclaimers). It uses infrared signals (similar to your TV controller) to send signals to an on board chip via 1 or 2 sensors. An advantage over radio control is that one transmitter can control multiple locomotives simultaneously.

 

Another is that the control gear required in the locomotive takes up a fraction of the space in comparison to that required for radio control and the cost of components is lower too.

A disadvantage is that it cannot be used (yet) out of doors due to swamping of the sensors by daylight. So what does one need?

What's Needed?

Parts for battery and infrared controlThis picture shews many of the parts required. A manual is provided detailing how to go about the process and how it works. A number of rechargeable batteries. This will be dependent upon the current drawn by the motor/gearbox combination and the space available for them.

 

Battery technology is advancing rapidly these days, witness the current lithium ion cells powering mobile phones for days on end and requiring only four hours to charge. While such wonders are not yet available to us, the improvement in bulk to power ratios in rechargeable batteries compared to even a few years ago is dramatic and continuing.

 

An infra red transmitter/controller, somewhat similar to a large TV remote control, capable in theory of controlling up to 99 motor/receiver combinations. I say in theory because it is probably beyond the bounds of most people to control that many locomotives at one time anyway.

 

A very small PCB - the receiver module - containing a programmable microprocessor, non-volatile memory and a couple of beefy transistors. It remembers the settings given it by the transmitter and passes your instructions on to the motor.

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A battery charger capable of simultaneously charging up to four sets of batteries at once plus the 9 volt battery for the control unit. (Provided the total amperage does not exceed 1 ampere.) Also necessary is a method of switching off the battery power from the receiver module when the locomotive is not in use or the batteries will eventually go flat due to a very low, but constant, current draw.

 

For this there are reed switches and or small manual circuit breakers based on computer shorting plugs. A suitable length of heat shrinkable sleeving for the batteries. There are various other sundry parts that may or may not be needed depending upon how you wish to set up any particular locomotive.

 

The manual gives much information about their use. The first picture illustrates some of the basic parts with which I began in front of the (almost) complete engine. You can see the sensor in the bunker while the second picture illustrates the sensor and the lead for attachment to the charger. Before beginning any fitting at all it is ESSENTIAL to read the manual, preferably - as recommended by Exactoscale - prior even to buying any parts.

 

I found the method simple and easy to install provided one follows a few simple rules and instructions but, as with all other methods of controlling models there are potential dangers inherent in battery power.

 

Should a set of charged batteries become shorted the resultant surge of high amperage charge is capable of generating sufficient heat to destroy your locomotive and you could even suffer severe burns. Be warned!

 

I used circular batteries, rather like watch and camera batteries but much larger.  At 25.1mm diameter by 9mm thick a stack of 6 will be a little over 54mm long and provide about 8 volts at 280mAh. This will give several hours running using a 6 volt motor with a good gear box, in this case a Maxon in an ABC gearbox, but a Portescap or similar would do just as well (3 and 6 volt Portescap motors - I am told - are available but hard to find however, ABC can produce motor gearbox combinations to order, (usual disclaimer)).

 

However, there are smaller sizes of battery available that will fit smaller boilers. There are also other shapes and sizes that can be used for fitting into tenders for instance. These batteries were the largest available at the time and were chosen because they would just fit inside the boiler and smoke box of 848 with the motor reaching back into the firebox, thereby placing most of the weight over the front drivers.

Fitting

Now to the actual fitting. These are not tagged batteries so care was taken soldering some phosphor bronze wire (strip would have been better) to the negative side of one battery and the positive of another. One lead should be longer than the total length the stack is going to be to reach from the base to the top of the stack.

 

I used just a trace of Frys flux paste on the battery surface with standard electrical solder on a clean 25 Watt iron with pre-tinned wire, now I would use C&L solder cream instead.

 

One touch is all it takes so heat damage to the battery is unlikely. However, if at first it does not take, let it completely cool down before trying again. The batteries have a potential in them when delivered so it is an easy matter to check they are still OK after fitting the wires.

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It is necessary, thoroughly to clean the batteries to prevent them corroding once they have been sealed up. I used acetone for this and was then careful not to handle them by their flat surfaces. The edges are encased in plastic.  The battery with the longest wire was put into a suitable length of heat shrink sleeve followed by the rest taking care to stack them Negative to Positive. Using a fairly strong heat source (my wife's hairdryer) I shrank one end first. This gave a firm base to pack the batteries to be in good contact before shrinking the rest of the sleeve.

 

Frequent checks with a meter help ensure electrical continuity. Before completing the shrinking process I soldered red and black wires for positive and negative to the relevant phosphor bronze tags. This is essential to avoid an expensive and possibly dangerous situation of the batteries being connected to the charger with polarity reversed.

 

Then the stack was checked to make sure that it would fit in the boiler.  It was a close fit but not tight and can be removed easily for eventual replacement. The battery pack was then removed and put on charge for three or four hours.

 

The next part of the process was to test out the whole set up before fitting anything in the locomotive. Leads were connected on the board containing the chip to the motor and the sensor. If fitting a magnetic reed switch then this should go into the circuit too and have a magnet ready to test it out.

 

The manual has very clear wiring diagrams. I decided to fit a computer shorting plug to disconnect the power when not in use. This is probably a good idea anyway since it is a permanent method of shutting off power so that the chip circuitry does not drain the batteries when the engine is not in use.

 

The reed switch is intended for temporary switching out when parked over an electromagnet set between the tracks. When I was satisfied that the wiring was correct, power was connected and the set-up tested with the chassis on a rolling road.

 

Then came the interesting part of fitting the parts in the locomotive. The batteries were easy and simply needed gently pushing down the boiler barrel as far as they would go, friction held them in place but the blue tack was at the ready just in case.

 

The circuit board took a little more care. I filed down all the solder points on the back (very carefully of course!) Once they were nice and flat, two layers of masking tape sufficed to insulate it from the locomotive body. It was placed in a bed of blue tack (such useful stuff) in one of the tanks and then it was checked for fit to ensure the whole thing cleared the motor and wheels when the chassis was put back.  The transistors do need some air space since they dissipate heat, another reason why low amperage motors are essential.

 

The blanking plug was fitted by first encasing it and its attendant wires with epoxy to some 40 thou. Plastikard that had been cut a tight fit inside the other tank. An important point to bear in mind is to use multi-strand wire for all these connections. This ensures there will be no shorting or intermittent faults due to fractured wires.

 

The internal framing was filed away to leave a gap for the pins to project through for easy removal of the shorting plug. Then the whole thing was epoxied in place. However, before doing this I should have double checking the wiring. I had not with the result it had to be taken it out again, which was a pain.

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Fitting the electronicsThe blanking plug is easily fitted using a small pair of pliers and is invisible. When not in use it lives in a little bag in the locomotive's carrying box. The wiring inside the body was arranged to make sure it did not foul the motor or gear box and is held in place with the ubiquitous blue tack.

 

Infrared pickup.The sensor was fitted in the bunker where also are stored the leads for connection to the charger and so the various wires were found a clear path to holes I had previously cut in the base of the bunker. I have yet to put coal in and disguise the sensor as a lump of coal, but this will be done with a piece special black plastic sheet that can be molded in hot water to represent coal.

 

It replaces the green cover over the sensor but is transparent to infrared signals. There are detailed methods described in the manual for charging via the wheels on an isolated section of track and even via the buffers. They require a bit more in the way of electronic circuitry but do not appear difficult.

 

Eventually I shall add another sensor beneath the front of the locomotive, so that the signal can be received anywhere by reflection. The chassis was refitted and the controls tried out again on the rolling road. If a reed switch had been fitted, now would have been the time to test it again.

 

Then the motor was run until it stopped and left overnight without removing the shorting plug. This ensured the batteries were completely discharged. It took about fourteen hours to charge the batteries then the engine was set up running on the rolling road thoroughly to check out reverse, acceleration and deceleration, etc.

 

Then it was run until the batteries went flat as before for recharging from scratch. I recommend this is done at least three times so that the batteries get properly conditioned. The sensor to pickup the infrared signals fitted in the bunker and would eventually be hidden under some coal.

517 No: 848 ready to roll.No: 848 will now run a little short of four hours continuously at full bore, it also is capable of hauling considerably more than its own weight. I am pleased with the results and intend to use it in an early Wolverhampton 517, a 2-4-0 River Class and a 1501 0-6-0 saddle tank currently under construction.

 

This method of control allows the prototypical use and allocation of locomotives as well as ensuring that they are driven correctly. An important point is that one can still run locomotives so fitted on 'ordinary' tracks so I can run it on the club layout. The next phase will be to build the track (without wiring or electrical breaks and "gubbins"!) and use mechanical operation with full interlocking between points and signals. Then I shall have to learn the rule book properly!

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Exactoscale maintain that this method can and has been used in 4mm scale locomotives. I can certainly see that the larger tender engines would be easy and there is little doubt in my mind that it would also fit into the early versions of the 517 with the smaller cabs in 7mm as well as a number of other small locomotives. I think, with the smaller diameter batteries, it would be relatively easy to fit the system into the 4mm version of Malcolm's 517.

 

For those who wish to avoid electrified rails and their attendant problems and or work more realistically, then I recommend this as offering the easiest and most cost effective method I have so far investigated.

 

I have described the Mk I version here. There is also a Mk II version that will allow control of locomotives in locations where one cannot directly aim the controller by using a system of repeaters around the layout.  The Mk I can be retrospectively upgraded to Mk II without changing any components in the locomotive.

 

Published originally in the Gauge O Guild Gazette August 1999.

Afterword

Ultimately I did not pursue this methodology because I was seduced by the sound capability of DCC and so moved on to the ZTC system and back to electrified tracks.  However, all tracks are constantly powered at about 20-25 volts AC so should present fewer problems.

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