Animating a train order board

StW-Station-Order Board photo StW-Stn-OrderBoard-01_zps149435a9.jpg

Errands today took me past a hobby shop that specializes in radio control models – everything from cars to boats, aircraft and helicopters. And given that R/C models tend to take a lot more abuse than model trains, the store is very well stocked with replacement parts. That’s good news when looking for components to animate a train order signal.

The young guys behind the counter gave me puzzled looks when I asked for “bell cranks”. Their first question was, “For what car?”

The guys were even more confused when I said, “Not a car – for a train”. We then proceeded to communicate through the waving of hands. (This reminded me of conversations I had while travelling in France a couple of years ago, when I realized that my never-great command of French had pretty much abandoned me within months of graduating from high school.) But eventually the fog lifted and I learned that what I needed was a set of Servo Horns. There was an extensive selection – as many Servo Horns for the R/C hobby as there are boxcars for ours – but I settled on one of the smaller offerings, part S3103 from Futuba:
StW-Station-Order Board mechanism photo StW-Stn-OrderBoard-02_zpsd06282c7.jpg

When I got home I started working my way through the mechanism and two hours later I had bodged together something that – while not pretty – is robust, smooth, and maintainable. It’s entirely mounted within the roof of the structure, and designed to slide down a hole drilled in the styrene base I installed yesterday while creating the cinder station platform.

Here’s a close-up of the mechanism, labelled. (It’ll help to refer to this as you read the rest of this post.)
StW-Station-Order Board mechanism photo StW-Stn-OrderBoard-03_zps72459f52.jpg
(Click on the image for a larger version)

Construction was straight-forward, if a bit ad-hoc. (Yes, I made it up as I went along…)

I started by adding four pieces of wood inside the roof to key into the walls of the station. I simply held the roof in place on the walls and installed the wood from the underside. (I used wood because I had wood of sufficient size on hand. Styrene would have worked too.)

Yesterday, I had installed a pair of braces inside the roof. These are joined by other pieces of styrene that support the control rod that passes through the roof to the signal, and create stops that act on a piece of styrene attached to the control rod to limit the rod’s travel. This in turn limits the rotation of the signal to 90 degrees. I installed the first stop, set the signal, slid a pre-drilled piece of styrene onto the rod and up against the stop and glued the styrene to the rod. Then I set the signal for the opposite indication and glued a second stop in place so that it just touched the travelling styrene piece. Easy-peasy.

Today, I cut a piece of .060″ styrene sheet that would be glued to the side of one of the braces. Before gluing it in place, I marked out the location of the pivot for a Servo Horn, which I cut down from an “X” shape to an “L” shape. I built up a supporting block to centre the Servo Horn between the roof braces and drilled a hole into which I threaded a 2-56 screw. I hung a piece of piano wire on the Servor Horn, then took my station to the layout, drilled a half-inch hole in the platform base, and threaded the wire through. This helped me determine how long a piece of brass tube to use as a sleeve for the piano wire.

The brass tube is threaded onto the piano wire and glued inside a length of styrene tube using CA. The styrene tube is then glued to the .060″ sheet. I filed a flat edge in the styrene tube to improve the glue join, and then braced the tube with a pair of styrene I-beams, capped with a scrap of .060″ styrene sheet. (Yes, the brass tube is mounted at an angle. No, it’s not a problem.)

I bent the far end of the piano wire into a small square – roughly a quarter-inch square, so small enough to pass through the platform hole – then cut off the excess length. This square will be used to connect the order board mechanism to a Bullfrog manual switch machine, mounted on its side under the layout. Meantime, I’ll fashion a pipe-clamp to hold the brass tube in position on the underside of the layout. This will keep the station roof from lifting when the mechanism pushes the piano wire up – while also allowing me to disconnect the clamp and lift the roof off the station if (when?) I need to get at the gubbins.

I’ll need to put a coat of black paint on the mechanism and the interior of the waiting room. It shows through the window and door. But some slightly dirty glass will help with that too…

Oh – and I’ve painted the target red!

4 thoughts on “Animating a train order board

  1. Trevor,

    Well done. I enjoy your suggestions on how to tie the operator to the scale world.

    A couple of mechanical design suggestions for yourself and others following your design, if I may.

    It is a best practice to limit the the robust, driving item. In this design, that would be the bell crank. This may be accomplished with bonded blocks or pins placed to limit the rotational movement of the crank. These are placed once the full movement is determined. This prevents the more fragile item, the smaller diameter control arm here, from buckling if one pushes the main control arm (piano wire) too far. An additional stop may be placed on the train order box to limit the throw there to a shorter distance, offering further protection for the delicate items further down the line.

    Additionally, the wire passing through the bell crank should be bent as an “S” shape with straight legs, rather than a “U”, such that the wire may be easily inserted into the crank without having to unbend the control wires yet prevents the wire from skipping out of the crank hole.

    Keep the interactive animatronic ideas coming. I look forward to using them on my own layout.


    Rick Uskert

    • Good suggestions, Rick – thanks for making them.

      I too have been thinking about the stops. Now that I know the mechanism’s required travel I can go back and add pins to act on the bell crank.

      My first control rod was bent in an S shape – it interfered with the fine wire to the signal. So I recent as a U. It means I have to unscrew the bell crank to remove this rod, but I can live with that.


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