Trolley mechanisms from parts

I’ve blogged about this before but I’ve thought a lot  about the design of model trolley mechanisms and how they could be designed. The tricky part is that a prototype trolley rode on much smaller diameter wheels than a diesel engine. For the modeller trying to find a source of parts this rules out simply taking a proprietary diesel chassis from something like an off-the-shelf Kato model and just stuffing it under a shell. Since the whole design, in my opinion, is hinged on finding an appropriate source of wheels and is tempered by the fact that I don’t own a lathe and can’t machine my own. What I wondered about was if there might be a serendipitous combination of the wheels from one scale used in another one.

To see if this balance might exist somewhere I created a simple table and chose the typical 42″ diameter diesel wheel. This table shows the equivalent diameter of that wheel measured in other popular model railroading scales:

1/160 1/120 1/100 1/87 1//64 1/48
1/160 42 56 67 77 105 140
1/120 31 42 50 57 78 105
1/100 26 35 42 48 65 87
1/87 22 30 36 42 57 76
1//64 16 22 26 30 42 56
1/48 12 16 20 23 31 42

As I guessed the balance does work out. I was happy to see that 1/100 scale using parts from N works out really well. I’ve highlighted the instances where we arrived at our 26″ wheel exactly (in blue) and then also highlighted those instances where we got pretty darned close.

What else do we gain beyond just the correct wheel? The wheel diameter is really the big pitch here but along the way we could reap some other benefits. By using coarse scale proprietary wheels in a larger scale we could actually approach finer scale tolerances. Of course the reward is that we can then start sourcing geared axles or even complete trucks from that smaller scale. While we don’t need the Blomberg sideframes from an N scale Atlas GP-7 that geared drive is very smooth and just about perfect – much better than anything I’d ever create.

Any other benefits or parts we could use? N scale doesn’t suffer as much these days for this but manufacturers supporting the N scale market were often forced to make compromises in the models they offered to accomodate motors and similar parts. Often this meant that the model you bought just turned out larger than it should be. We know that N scale trolleys like the Bachmann Brill and Model Power TTC four-wheeler are too large for N. I wonder how close they scale out in, say, 1/100?

I think the next thing to find out is to exhume one of those Atlas RS-1’s I have packed away in the attic and see how well the truck’s overall dimensions compare to a Brill truck.


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