Attn: Interurban modelers

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"
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To get the axles turning at the same speed, you need to use the same size gear on both axles. In any simple gear train the idler gears do not affect the ratio, only the first and last gears in the train determine any change in rotation ratio.
walt
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Have you thought about using N scale flexcoil trucks replacing the end axles with longer ones and adding HO scale 33/36" wheels? leave the center axles to be hidden by the side frames. That would give you a wheelbase of 7 feet.
Eric
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Thought about it but haven't had an example to work from. Can they handle .092" axles? Did you have a certain brand/model in mind? I'd like to keep the interior as clear as possible.
Jay CNS&M North Shore Line - "First and fastest"
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Jay Cunington wrote:
"Thought about it but haven't had an example to work from. Can they andle .092" axles? Did you have a certain brand/model in mind? I'd like to keep the interior as clear as possible."
I haven't actually done this myself but I've heard it discussed and seen a model [steeple cab] that was done like this.
Take a look at the Atlas exploded drawings of the locos.
http://www.atlasrr.com/highlights/parts.asp
One would need to:
Lengthen the wheelbase of the chassis to the correct length
Replace the truck axles with longer rods and figure out how mount correct diameter wheels on it.
Figure out how to extend the wipers to the reach the new wheel gauging.
Before going into all this check to see if the Bachmann 44 tonner trucks would work for you. Would be alot easier.
Eric
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