In this post I describe the roof and lighting for my diagram N4 GWR horsebox, following previous posts detailing the build process for the underframe and body.

 

Before getting into the nitty-gritty of the construction, I want to say a few things about why I chose to light the interior of the horsebox. My plan is to be able to run Netherport, when it is finally built, in night mode - or, more accurately, dusk mode: the last light in the sky, lamps starting to be lit in buildings, and of course in passenger trains. I have ambitious plans for a theatre-like cyclorama sky, on which sunset can take place. Partly this is inspired by my earlier career as a theatre lighting designer, but even before that, memories of visiting Pendon as a boy in the 1970s, and seeing the Dartmoor scene in its night state, with the lit train crossing the silhouetted viaduct.

 

The horsebox seemed like a good starting point for experimenting with coach lighting - only one compartment to be lit, and planty of space for whatever electronic gubbins is required. Most people use LEDs for this purpose, and it's easy to understand why - they are small, cheap, have a very long life, and use very little power. However, they have one big drawback - colour. Nominally, you can get LEDs in a variety of shades of white, from warm whites (yellow/orangish) to cool (bluish), but the issue is that the spectral output is not that of a naked flame or heated lamp filament. I won't get too technical here, but the upshot is that warm white LEDs are almost always a bit pink or a bit acid yellow/green, not a true warm white.

 

There are two disadvantages to this - firstly, the colour of the light looks wrong, and secondly, there is a risk that colours are not rendered properly. Due, I suspect, to my professional background, I am particularly fussy about light colour, and I am sure many people find LEDs perfectly acceptable. I also think it may be possible to find LEDs that would meet my needs, but I haven't managed to yet.

I did some experimenting with small filament lamps, and found that a 12V, 60mA lamp run at half voltage gives both a good colour for the naked flame of an oil lamp (which these horseboxes were equipped with), and the right brightness to light the compartment in subdued room lighting:

 

 

As an aside, please don't judge the colour of light in these photographs - or, probably, any photograph. There are many steps going from the light in my room to the light that enters your eyes when you look at your screen, and there is no overall control of that process to ensure consistency and accuracy.

 

Having established a light source that would get me the effect I wanted, the next question was control. After a bit of research, I chose the ESU Lokpilot 5 FX as a DCC decoder - the FX version does not include motor control, it just provides control for accessories. A key advantage of this decoder is that you can set it to provide a slight fade in and fade out on the lighting outputs, rather than a snap on and off. This seems better for an oil lamp.

 

Here is the decoder being tested with the lamp and a 100R resistor wired in series to drop the voltage to the required 6V:

 

 

The test rig has a small circuit board with an 8-pin DCC socket to plug the decoder into, wired into 'choc-block' connectors. The circuit board was a cheap eBay purchase, and very handy. I also used one in the finished horsebox so the decoder can be easily removed if necessary.

 

I added a 'keep alive' to the circuit, using the design given in the ESU documentation, although this seems to make very little if any difference:

 

 

With the plan for the electronics sorted, I moved on to the roof. The kit includes a brass roof, ready formed to the required profile - though it did need some tweaking. I felt it was important the three sub-assemblies (chassis, body, roof) remained separable, for access to the interior of the grooms compartment in case of dust or parts becoming detached, and to the electronics. I arranged for a length of studding to go vertically in the centre of the horsebox through a hole in the chassis floor, to a nut soldered to the centre of the roof. I soldered a nut to the bottom end of the studding and cut a slot in it to take a screwdriver. tightening the studding clamps the roof down onto the body, and the body onto the chassis, holding everything together. I made the roof with slightly too much curvature, so the sides of the roof are clamped down onto the body first, so avoiding any gaps.

 

To ensure the roof didn't bend in the middle, I soldered a piece of brass channel along the centreline, stiffening the roof lengthways. The nut was soldered into the channel:

 

 

In the above picture you can see the roof has been sprayed white - this was after covering the top side with model aircraft tissue, glued on with the relevant dope. This gives a nice, subtle texture, which worked well with the weathering later on.

 

 

The lamp was attached to two lengths of copper wire - stripped out from a bit of 'twin and earth' electrical cable. The idea is these help draw the heat away from the lamp - the lamp runs at about 50mA when at 6V, and that current also flows through the dropper resistor, so that's 0.05A x 12V = 0.6W of power being dissipated. Not huge, but it's a confined space and I would rather get it away from the delicate compartment interior as quickly as possible.

 

 

And with the copper wire trimmed:

 

 

At the other end of the roof (the 'kicking' end) I added a small PCB connector on a piece of stripboard, so the roof could be disconnected when required:

 

 

The final detailing of the roof involved adding rain strips from plastic strip, the oil lamp top and the ventilator. The kit includes a nice cast 'trumpet' ventilator, but by my 1908 period these had been replaced by gas lamp tops. There is no lighting in the horse compartment - the gas lamp tops were used purely as vents.

 

 

The oil lamp top was a nice casting, with dimples where the holes should be, but the appearance can be improved by drilling these out with a 0.5mm drill. I realised it would be possible to drill up through the centre with a larger drill, and have the small holes meet in the middle. The lamp top of course has the actual lamp directly below, so a little light comes out of the vent holes, which you can just see when it is dark. In reality, this almost certainly wouldn't happen - there are too many baffles controlling the air flow for light to come out - but I couldn't resist this little piece of theatre.

 

 

The final element of the lighting system is the pickups. These were made with phosphor bronze wire, rubbing on the edge of the flange. For each of the four pickups, I soldered a short length of fine brass tube to a piece of stripboard, and also soldered on a length of flexible electrical wire. These units were glued under the axles, with a piece of plasticard to pack them up so the pickups would clear various obstructions:

 

 

The phosphor bronze wire was then added, bent into a right angle and fed into the brass tube. A dab of solder fixed the wire to the tube. Doing it this way allowed me to adjust the tension of the pickup wire against the wheel at the moment of soldering.

 

The four wires were routed above the chassis floor, held in place with some plasticard 'cable guides':

 

 

I tested the pickups with a temporary setup comprising two of the 12V lamps in series, driven by the DCC power, without the decoder. This showed that the pickups work OK as long as the wheels and track are scrupulously clean, though with some occasional and very slight flicker, especially when changing direction. The keep-alive circuit doesn't seem to help much with this - once in use, I will have to see if it is acceptable or not. Plan B would probably be some kind of battery or super-capacitor set-up, constantly topped up by the DCC power.

 

 

I added another connector, so the chassis can be disconnected from the rest of the electronics:

 

 

The keep-alive circuit and the PCB with the DCC 8-pin socket were glued to a plasticard construction to stop them falling about inside the body, with the risk of a short circuit. You can't see if very easily here because of all the wires, but hopefully you get a sense of it:

 

 

A final addition was this plasticard item - a block with a conical hole to guide the length of studding into the nut when putting it all together, glued to the roof:

 

 

And all this work is so our groom can read his paper after dark:

 

 

In the gathering gloom, the train slowly makes its way, taking groom and horses towards their destination...

 

 

 

 

Nick.