The White River and Northern Model Railroad

Wiring Diagram

    

Powered N Scale Hi-Rail

With the advent of affordable and easily available pager motors came all kinds of animation possibilities. It wasn't long before I decided to try my hand at powering an N scale hi-rail, and do so with as few compromises to its appearance as possible.

Although I'd wanted to start with an earlier era vehicle, the modern GHQ hi-rail (which I can no longer find in their online catalog) offered the advantage of having all of the details needed for such a model.

The scrap box yielded a perfect worm and gear set for the drive; the worm very nicely press-fit onto the pager motor shaft, and a slight drilling of the worm gear allowed it to press onto the wheel axle. The motor is simply held to the chassis with a steel wire clip.

The chassis is a scrap of brass channel stock drilled for the two axles. Northwest ShortLine fine-flange, narrow-tread wheels were fitted to the chassis; on their insulated side, small rectangles of printed circuit board, sanded very thin, were bonded in place with CA. Two small scraps of phosphor bronze were cut to length for wheel wipers.

The truck body required a fair bit of grinding with a Dremel tool to make clearance areas for the motor, worm, and wheels. I drilled a sheet of thick styrene with a bit that matched the diameter of the motor, then cut away the excess to form two U-shaped parts and bonded them inside the truck cab; these simply press-fit onto the motor to hold the body in place. The only compromise to appearance was the end of the motor protruding ever so slightly into the truck bed, which would be easily disguised with a toolbox.

I'd wanted the model to run on a normal DC power supply, but the pager motor runs on 1.5 volts. So, I utilized the old trick found in many constant-brightness headlight circuits: two pairs of diodes facing back-to-back. They're connected to a 12-volt GOW bulb for ballast (the side benefit being the truck lights can be illuminated). Everything is tucked inside the chassis, under the motor.

Given that the pager motor had no leads or solder lugs, I had to devise a way to get power to its single end terminal. I soldered a coupler spring onto the end of one of the diode leads such that the spring pressed against the motor terminal; the chassis itself provided the other connection. The motor is attached to the chassis with a simple steel wire clip.

Sadly, even with its nice heavy pewter body, it can just barely haul itself along on level track, and won't make it up any kind of grade. The speed range is wider than I anticipated, but slow speed operation is rather unreliable owing to its extreme light weight, which is no surprise.

It doesn't like most turnouts, especially those with plastic frogs or wobbly point rails (curiously, it has no trouble at all on my Code 25 turnout...); it also has problems on any track where the gauge is less than perfect—it will actually drop down between the rails on occasion. So, while it does run under ideal conditions, it's little more than a curiosity at this point, which is why I have not finished it.

Image specs: All photos were taken with a Canon PowerShot SD400.

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