Plymouth Switcher

Plymouth Model BL locomotive - From rough to restored...
Looking at compact model train layouts, thinking maybe I need a mining railroad, lots of turns and hills and bridges and stuff. Tight turns require small locos, like this compact switching engine, which is how I stumbled over this video. The reason it is here though, is because it uses an infinitely variable mechanical transmission / clutch to transmit power to the wheels. It has two large wheels, one which is driven by the engine, and the other, driven, wheel is positioned at 90 degrees and mounted on a movable shaft. The engineer employs a hand crank to slide the driven wheel left or right along its shaft. By doing so, he selects the speed and direction of the locomotive. He then uses the large control lever to force the driven wheel against the driving wheel. It is not a perfect arrangement, there is going to be some slippage due to the geometry of the contact point, but with enough force it can evidently be made to work. I have heard of these kind of transmissions before, but the only place I can recall hearing them used was in the old mechanical artillery computers used on battleships in WW2 (start at the 8:55).

Rochester & Genesee Valley Railroad Museum had this engine, but there is no more recent mention of it on their webpage.