The creation of working OFF indicators & RA repeaters in OO Gauge, mounted with Next Train indicators just like you see at the station.

 

About

 

OFF indicators are used to aid Guards & Despatchers during train despatch, they are used when signal sighting is obstructed due to platform curvature, length or placement.  When the signal is displaying a proceed aspect, the OFF indicator will illuminate.

 

RA 'Right Away' repeaters are used to despatch DOO trains - either ECS or service trains depending on location.  They too are used when signal sighting is obstructed so the driver can easily see the indication.

 

NTI 'Next Train Indicators' displays are the three line displays usually found on the platform that indicate the next trains departing.

 

I was going to post a prototype picture here from Bristol Temple Meads but it was complete before I had a chance to get one.  I may come back and pop one in here, we'll see.

 

Here I will recreate a island platform NTI display with OFF and RA indicators, for this I will use the 3D printed versions from Mainline Models - they have been designed using technical drawings from Unipart Dorman, a major provider of signalling infrastructure to Network Rail.  They are made available through Shapeways, a 3D printing marketplace based in The Netherlands. Links: OFF Indicator, RA Repeater.

 

They are shipped from Shapeways as printed, in a clear 'Fine Detail' plastic.  Shown with Peco Code 75 track for scale.

 

 

Materials

 

To contruct the structure I will be using:

• 4.8mm Square Tubing (Available from Evergreen Scale Models & Plastruct among others)
• Polystyrene Sheet (Plasticard)
• Next Train Indicators printable kit (Purchased from ModelRailwayScenery.com)
• Pre-wired #1206 SMD LED's (Purchased from eBay)
• Black Paint (I used Tamiya Dark Iron)

 

 

Construction (Time to compelete 4 Hours)

 

Once I received the Indicators from Shapeways I saw that some of the holes had webbing over them so the first task was to push a thin needle through those holes to ensure they were open, then I could begin painting them black to match the prototype.  Following the painting, again I pushed the thin needle through the holes to ensure they hadn't been bridged by the paint.  The plastic does take the paint reasonably well but does require 2-3 coats to get complete coverage - I used Tamiya Dark Iron. It's helpful to paint the inside first, this way you can hold it up to the light and easily see any gaps in the paint.

 

When the indicators are held up to light the effect can be seen (before the back and sides are painted) - the close-up photo shows scratches from the needle when I was clearing the holes, I didn't notice these when I was checking them so I am confident they won't be seen from 'viewing distance' - or even with the naked eye from a normal distance!

 

Now to think of the LED's, here is one of the #1206 pre-wired LEDs.  This is the size recommended by the designer in the Shapeways product description.  Personally I think it looks a bit small but I will need to get a power supply set up and see how it looks - if needed there is space for up to three LEDs per indicator.

I don't have a bench power supply - I don't even have a proper workbench - so I will use a spare 12v wall plug and wire it to some veroboard putting a resistor in line with the LED, this will also let me test the brightness and pick the best resistor value to use.  Maybe I should invest in a breadboard for things like this so I can leave the soldering iron away for testing but for now it will do.

 

 

I started out with a 1K resistor which was much too bright and made me realise I needed to touch up some of the paint on the back and sides of the indicators!  I then tried a 10K resistor which was rather dim compared to what I needed.  I settled with a 4K7 resistor and facing the LED 'backwards' - that is to say facing away from the holes - in the indicator, this value gave fairly consistent lighting of the indicator.  Each indicator has a small slot in the bottom for the LED to slide into.  I am using 12v to power the LED although other voltages can be used, the required resistor value can be calculated using the formula: Volts / Current (0.0025) = Resistance (Ohms).  The current value of 0.0025A was calculated from my values of 12v and 4700 Ohms.  For example, to power the LED from a 5v supply the resistor value would need to be (5/0.0025=2000) 2K.

 

Next, I moved on to the NTI Displays.

 

Like many printable card kits; the Next Train Indicators kit contains a template page which needs sticking to card before cutting out, I used an empty cereal box, and also has a 'wrap' page which needs printing and wrapping around the carboard structure built with the template.

 

I stuck the template page on to a cereal box using Pritt stick before using a sharp scalpel to cut around the edges - before doing this I did draw some 'flaps' onto the template to stick them together to provide a solid 'base' for the wrap around.

 

The parts look quite a bit smaller once they've been cut out so I opted follow the instructions properly and use the wrap to hold together the template pieces, it's almost as if someone has thought about this!

 

After the first attempt using card, I gave up on it.  The card I was using was too thick and it is all I had to hand so I went on the search for something else I already had and that I could use that was thin enough.  That's when I found some thin Plasticard I could use, this seemed ideal as I could easily bond it to create a solid base to put the wrap over.  So I set out cutting out these shapes again for the second attempt.

 

I achieved a much better outcome with the polystyrene sheet with two cut and prepared in the same time as I managed one crude cardboard version, on to the wrapping.

 

After wrapping the first display I noticed a couple of problems, mainly with my cutting accuracy.  When I make more I will be taking more time and care, I will also probably discard the coloured wrap and just paint the plasticard instead and stick to using the kit as a scratchbuilding guide.  I will however be using the orange text in future builds.  I'd still highly recommend the kit but again, recommend it as a guide rather than a kit.

 

 

Finally, on to the mounts.  As I mentioned I am using 4.8mm square tubing, which, to be honest, does look a little over-scale once cut down to size but not to a huge amount.  In future builds I would probably reduce this to 3.5mm - 4mm tubing.

 

I chose to use tubing as it would allow me to run the wires inside to I only have short lengths of it to tidy up.  This will mean I need to cut a small section out of the bottom of the horizontal part for the wired to run through.  I used a spot-face cutter as I had it on the desk from making the LED testing circuit.  Because of the sharp turn the wired would need to take, they needed to be fed through before sticking the two parts together.  Ample wire was provided on the LEDs for this without having to extend anything.

 

The screens and indicators are attached to the mount with thin strips of plasticard - I am using Pritt Stick to attach them to the displays and Loctite to attach the painted indicators, I am using liquid poly to attach to the mount.

 

Once the indicators and screens were fixed to the mount, I pushed the LEDs into the indicators before securing the wires by adding some PVA glue,  just around where the the enter the bottom of the indicators, with a cocktail stick.

 

Then it was just time to paint the whole assembly before wiring it up for a test run.

 

 

Final Outcome

 

Overall I am quite impressed with what I have created in a relatively short amount of time - no more than 5 hours over two days!

 

I am very impressed with the appearance of the 3D printed OFF and RA indicators and will definitely buy and use them again.

 

As I said above, next time I will use the Next Train Indicator kit as more of a guide and only use the orange text screens on a plasticard base.  This should give a cleaner looking display as well as a stronger build and I can use liquid poly to hold everything together rather than Pritt Stick.  I think I would also look to fill in the slots of the RA and OFF indicators after the LEDs have been fitted, this way I can paint the bottom black too.

 

Also, looking at the illumination, maybe it would be wise to use two LEDs per indicator for a more even light.

 

Here is the final outcome:

 

 

and here is a video of it working:

VIDEO - Apologies for the screaming three year old background noise, she was jumping on the bed pretending to be 'SuperLucy'.

 

This is something I will re-visit when I have space and a plan for a layout, then I will work on ironing out some of the inadequacies of this project.

 

Cheers

Fred