How to build battery locos for your garden railway - Part 3 - Semi-scratchbuilds

This is Part 3 of a series of posts about building your own battery powered large scale locomotives. The other parts are:

• Part 1 - Kits
• Part 2 - Modifications and conversions
• Part 4 - Scratchbuilds (pending)
• Part 5 3D printing (pending)

In Part 1, I explored various forms of kit-building while in Part 2 we examined ways in which toys could be modified or track powered locos could be converted to run on battery power. In this part we shall explore ways of scratch-building your own body-shells to be mounted on commercially available powered chassis, motor bogies or motor blocks.

I will cover:

• Choosing a prototype
• Sourcing a powered chassis or motor block
• Constructing the body shell
• Wiring everything up
• Finishing touches

Choosing a prototype

Of course, your loco doesn't need to be based on any particular prototype, it can be purely imaginary. However even so, your loco might well be influenced by one or more real life locomotives, to make sure it looks reasonably realistic or plausible.

Over the years, I have scratchbuilt several loco body-shells to be mounted on various commercial motor blocks and chassis. All but two of them have been based on prototypes, though none of them has been an accurate scale model. I like to say my locos have been inspired by the original.

You may have a particular loco which you have always hankered about owning. Maybe it's one which no one has yet made available commercially, or maybe your finances are such that, although it could be bought off the shelf, you don't have the resources to purchase it.

My choices of prototype have been influenced by:

a) The Southwold Railway - which I have always loved and had hoped would one day be restored. At least I can enjoy seeing locos and rolling stock which once ran on the Southwold running on my railway. I have so far constructed a Southwold Railway Sharp Stewart and an SR Manning Wardle.

Semi-scratchbuilt Southwold Railway Manning Wardle 0-6-2T loco on an LGB motor block

b) Locos which have taken my fancy when browsing through books on narrow gauge railways. As a consequence, I have created a model of a Davington Light Railway Manning Wardle and my idea of what a three foot gauge Fowler diesel loco might have looked like

Semi-scratchbuilt ex Davington Railway Manning Wardle 0-6-0T on a Piko motor block

c) Locos which approximately fit on to motor bogies which I had available. These include a Metropolitan Water Board Kerr Stuart, a Black Hawthorn 0-4-0 and a Schull & Skibbereen Naismyth & Wilson loco

A semi-scratchbuilt Black Hawthorn loco on an LGB motor block

Once the prototype has been selected, I then set about finding scale drawings for them. Mostly, these were available in books about the railway in question. Sometimes, however, I had to scour the internet either for drawings and/or photos which would help in the loco's construction.

Assuming I have been able to track down a drawing, I then photocopy it and work out how each dimension can be re-scaled to 15mm scale. This is easily achieved by identifying one known key dimension (eg the gauge of the track), measuring it on the plan and then working out by how much that dimension needs to be multiplied to make it appropriate for 15mm scale. For example, the gauge of the track in this drawing of a Southwold Sharp Stewart loco measures 21mm (ie 3' in 7mm scale). In 15mm scale, the track gauge should measure 45mm, so if I divide 45/21 I get a value of around 2.14. So, if I multiply any measurement on the drawing by 2.14, then I will have its equivalent in 15mm scale.

Sourcing a powered chassis or motor block

My next job is then to calculate the diameter of the driving wheels and the distance between them (ie the wheelbase). Sometimes these dimensions are also given in books or on websites which can save a bit of work. 

Armed with this information, I then have to track down a chassis or motor block which is as near to those dimensions as possible. I've found online forums to be useful for this. There's usually someone out there who can suggest a suitable motor block. In the case of the Sharp Stewart loco above, the nearest motor block I could find was made by Playmobil - provided I modelled the loco in 16mm scale. I eventually tracked one down on the German eBay site. 

A Playmobil motor block - the basis for the Sharp Stewart loco build

For locos in category c) above, the process as the reverse. I started with the motor block and had to scan the internet and my library for a suitable prototype. In many ways, this was easier though, for the Schull and Skibbereen loco, I merged the body of one loco with the chassis of another, basically because I preferred the shape of the body.

A semi-scratchbuilt Schull & Skibbereen might-have-been loco on a Bachmann motor block

For me, that's one of the joys of creating your own rolling stock - anything goes!

An alternative to using motor blocks from large manufacturers is to use those from small scale enterprises such as IP Engineering, HGLW, Garden Railway Specialists, Phil Sharples or Essel Engineering - particularly if you are running on 32mm gauge track.

An outside framed 0-6-0 chassis from Essel Engineering

Constructing the body shell

For me, this is the fun part - figuring out how to break down the drawing and photos of the loco into a series of parts which can then be put back together again as a finished loco.

The choice of material for constructing the body is entirely up to you - card, wood, plastic, metal or any combination of those is entirely acceptable. In the main, I have used plasticard, usually combined with metal parts such as handrails, spectacle rings and small whitemetal fittings. More recently, I have been using 3D printing for most of the component parts (more of that in Part 5 - pending).

My first semi-scratchbuilt loco was a diesel. There was a simple reason for that - I figured that the shape of a diesel loco is basically a couple of boxes glued together - one for the bonnet and another for the cab. It turned out to be slightly more sophisticated than that, but the basic concept is correct.

My first semi-scratchbuild - a Fowler diesel mechanical loco

I learned a lot by constructing this model, but the construction process I followed is more or less the same as I have used for all my semi- and scratchbuilds. I start with the running plate.

The running plate is, in effect, the interface between the motor block or chassis and the body shell. The outer dimensions of the plate are dictated by the measurements shown on the plan while the hole in its middle is determined by carefully measuring the motor block, I find this needs to be tweaked as the model takes shape to either allow for or give clearance to the rest of the model's superstructure.

I've found that making the cab is generally a good next step as it is a firm fixture on the running plate and its dimensions are usually fairly easy to identify. Although I may assemble its sides, I don't usually fix it to the running plate immediately as some tweaking my be required.

I like to make my cab roofs removable so I can more easily paint the interior and fix the driver in place and so i make sure the ribs for the roof are short enough to fit between the sides and are glued to the roof to fit inside the front and rear of the cab.

When making the bonnet (for a diesel loco) or boiler and tanks (for a steam loco), some thought needs to be given as to where the batteries and radio control equipment will be located. It's advisable to create as much uninterrupted inside space as possible so, if the boiler can be sliced off where it joins the tanks and the insides of the tanks can similarly be curtailed, then bear this in mind when putting them together as a unit.

I tend to do a lot of test-fitting as I progress with the build and try not to fit parts together until I'm more or less certain how and where they will go.

Incidentally, boilers can be formed from pieces of plastic pipe, plastic bottles or card or plastic tubing or, if you are unable to find anything of the right diameter, created by wrapping 1.5mm thick plasticard around a suitable wooden or plastic former, held in place with cable ties, and plunged into near boiling water. The coffee stirrers were used to help avoid corrugations at the ends of the sheet of plasticard, though I've since discovered it's better just to overlap the plasticard by a couple of centimetres and then trim off the excess.

An interesting problem which needs to be solved at some point during the construction of the body-shell is how it will be fixed to the motor block or chassis. Ideally, the two should be easily removable - but not so easily removed that the loco comes apart each time it is lifted off the track.

Over the years, I have tended to try keeping the number of mounting screws to a minimum. This can sometimes be achieved by allowing one end of the block to slot in under a bracket. The other end should then require only a single self-tapping screw (sometimes two) - to hold it in place.

If your body-shell is made from plastic, then you will need to add weight to the loco to improve its adhesion. I use strips of lead flashing which I bought in a roll from my local builders' merchant.

Strips of lead flashing sandwiched to make loco ballast

I now use clear silicone sealant to hold such ballast in place, having discovered that EvoStik has a nasty tendency to dissolve styrene or HIPS plasticard. Tailored strips can be squeezed into empty spaces......

..... or simply glued into cavities on the base of the loco.

Once the body shell is finished it needs a couple of coats of primer. I generally use Halford's car paint primer from a rattle can as I also use their range of car colours for my loco livery (Rover Brooklands Green and Satin Black). From experience, I know it is inadvisable to try using different brands of paint for priming and top-coating as they can react badly to each other.

Inevitably, there will be some filling, rubbing-down and smoothing before the top coats are applied, but it's important to iron out any blemishes if you want a decent finish.

Wiring-up your loco

If you are uncertain about which batteries to use, I would advise you to do your homework before committing yourself. A lot has been written about the dangers of using lithium-ion cells and LIPO battery packs but, if you are careful and follow guidance, they are a lot less dangerous than, for example, filling a loco's fuel tank with butane, setting fire to it and heating water in a pressurised boiler. For more information on batteries see A Quick Introduction to Batteries for Model Trains and Getting Started with Battery Power and Radio Control.

Your loco could have very basic manual control comprising an on/off switch or a direction switch with a centre-off position.

Alternatively, it might have an additional simple manual speed controller built into the circuitry. These can be bought very cheaply on eBay. They are wired into the input for the reversing switch - two wires in and two wires out.

Or, you may opt for a radio control system. 

If you decide not to use rechargeable batteries then the wiring can be made even simpler.

Finding somewhere inside the loco for the batteries is probably the greatest challenge, together with trying to decide where to put the switches and charge socket. They can either be positioned beneath the running plate or put in unobtrusive places on the loco body shell.

The on/off switch can just be seen below the saddle tank on my Black Hawthorn loco

Finishing Touches

For finishing touches such as safety valves, domes, whistles, tank fillers, backhead details, smokebox door handles, clack valves, handrail knobs, etc., you can either buy these are brass or whitemetal castings from suppliers such as GRS, ......

.... or make them yourself from offcuts, chunks of plastic filed to shape or 'found' objects such as the cap of a sun tan lotion bottle for a dome ......

..... or the side of a plastic castor for a smokebox door.

For more information see Repurposing 'found' objects for scratch-building

Conclusion

I was very anxious about constructing my first semi-scratchbuilt loco but after it was completed I couldn't figure out what I was so scared about.

My first semi-scratchbuilt loco - a Fowler diesel mechanical

Sure, I encountered a few problems, but I found ways of overcoming them. I know it isn't perfect, but when it's running on my railway I hardly notice its slight imperfections.

Over the years, I have slowly and systematically acquired new skills - mostly by learning from my successes and failures. I mentioned above that I had learned not to use EvoStik to fix lead weights in place - here's why ....

I can remember being very calm and philosophical about it at the time. It was just another setback which I needed to overcome. I dismantled that part of the loco (which by then was more or less finished), rubbed-down the offending surfaces, applied a fair bit of filler, rubbed down some more and then repainted it. If I look very closely at the loco, I can still see the slight undulations but I doubt anyone else would be aware of them - unless I pointed them out. After all, like motor cars, most locos which have had a good working life have a few dints, dents and scratches!

OK, there is some effort involved in making your own locos - but I believe that effort is more than repaid in watching a unique loco, which you have constructed largely from scratch, chuffing around your railway.

Here's that pockmarked an dented loco shown above in action .......