cc: Cream City Traction members
In trying to come up with a cheap gearbox for my North Shore frieight motor #458, I think I might have hit on a solution for freight motors at least. This may be able to be reworked to mount a small Sagami motor directly to the truck for passenger interurbans.
I stopped at the local hobby shop and raided the junk drawer. One of the things I brought home was what appears to be an Athearn EMD SD power truck. I've been wanting to use Athearn gears for this project because they're cheap and readily available. I've been playing with combinations of the 23 and 16 tooth gears to get a 6-1/2 foot wheelbase. I thought I had a winning combo, but the axles were turning at different speeds.
At any rate, I got the SD truck out and measured the wheelbase. It's 6-1/2 feet between the axles! I thought about chopping off the rear axle (the one farthest from the gear tower), but decided on chopping the front, because cutting the rear off would leave two retainer clips on the front, none on the rear of the truck. I cut the front axle off the truck at about a 40 degree angle (from horizontal) coming just under the forward rivet. I also cut off the "traction motor" detail at the rear of the truck. At this point the pivot point of the truck should be moved back from what was the middle axle to a point midway between the two remaining axles. This will allow me to drill through the metal at that point to let the truck ride on a #2 screw. I will need to fashion a mushroom-shaped extension forward from the point to get something under the ears on the worm gear cover to hold the trucks in.
I'm now thinking maybe I'll get another and bob the rear axle and see how that goes after all.
Since most traction trucks used 33-36" wheels, I need to do a swap with the stock Athearn wheels. Any flat-backed non-insulated wheel of the proper size will do as long as the axle is .092" in diameter (Flat backs are necessary to get the proper gauge). I mocked this up using Athearn passenger car wheels; they have humps on the back around the axles which leaves the gauge a little wide, so I can't test it on the track. I have about .040-.060 clearance from the flanges to the bottom retainer plate. The trick will be seeing if I can get it through a turnout.
I could probably raise the angle of the cut to 60 degrees and leave the gear somewhat exposed if I was going to rework this into my own gear case. That would hide more of the gearbox at track level.
Jay CNS&M North Shore Line - "First and fastest"