In another topic, the discussion turned towards how to deal with cars rolling down grade, and the topic of working brakes came up. This is something I’ve been toying with, though not with respect to parking cars on sloped sidings. In my case, I’m trying to do pretty much what the prototype does when pulling a train down a long grade–keep the train from bunching up and pushing against the locomotive. The problem–surging downhill, an unfortunate property of many worm gear drives when the grades are steep enough.
My dad’s Woodland Railway has a long stretch (100’ - 150’) of track with much of that being on a 5% grade. It’s definitely “helper district” for anything longer than 6 cars going up the hill. Coming down the hill, one would think there wouldn’t be any issue, but we’ve got a number of locos which surge something fierce on the steep parts of the grade. (Oddly, the threshold seems to be right about 4% for problems to crop up. There are many stretches of 4% grade on the line and the locos seem to run smoothly through those.) Anyway, if the train pushes against the loco as it’s running downgrade, it surges. If the loco is running light or its rear coupler is in tension such that the train is slowing the locomotive down, the surging goes away.
So, the question is, how do you build working brakes on the train so that you can successfully stretch the train against the locomotive so the couplers are always in tension while going down the grade? Since all trains on the Woodland Railway must have cabooses, the logical thought was to somehow create drag on the caboose so that it stretches the train. Some means of working brakes would hopefully do what we need it to do.
This is very much a work in progress. What follows is an early attempt at working brakes that works in some ways, but has some definite weaknesses.
This is what I’ve currently got in place. One end of the string is tied to the truck bolster. It’s then wrapped a few times around each axle, then passes up through the end platform to a brake lever:
This lever is currently on/off. There’s not enough wiggle room for “just a little” or “a little more” braking. Here, the string is being pulled, and the lever is in the “on” position. With the string in tension, it pulls on the string wrapped around the axles, creating drag and slowing the caboose.
Here it is in the “off” position; the string is relaxed and not creating any drag on the axles.
It works, but it’s not there yet. With the brake applied on a 6-car train, it creates enough drag to retain about half the train, so that the weight of only three cars pushes against the locomotive. That does seem to mitigate the surging, but I know it can be improved upon. A few issues:
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Because the string is wrapped around the axle, it creates more drag when the wheels rotate one direction vs. the other, causing the wheels to more readily lock up. Sliding wheels do create drag, but not as much as gently retained wheels, and without causing flat spots.
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The string has a tendency to bunch up, which also creates more drag and may lock the wheels.
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As currently implemented, the string leaves the end axle and goes up through the platform. This tends to restrict the rotation of the truck. On broad curves, this isn’t as much of an issue as it may be on tighter curves, but it may be better to run the string back towards the center of the truck so it can rotate more freely.
My thoughts at this point; I’d like to experiment with something other than string. I’m thinking a strip of fabric maybe 1/2" wide or something, wrapped in a “U” around one or both axles. My thought is this; tie one end of the “U” to the bolster, and the other end to a string which would go to the brake lever. You could have the ends of both strips of fabric tied together so that both are pulled tight by the lever. This would be towards the middle of the truck, so that would get rid of any issues with restricting the rotation of the truck. Also, because it’s a “U” shape, not wrapped multiple times around the axle, it would eliminate the bunching and uni-directional issues I’m having with the string. One could also experiment with different materials to see if they had any difference on resistance. My biggest concern is how to rig it so it applies the same braking pressure to each axle, but I’m also thinking it may be self-equalizing.
Has anyone else played with working brakes on their cars (electrical pick-ups don’t count; they can’t be applied and released. 
) There’s part of me that also wonders if it could be as simple as building working prototypical brake rigging with beams, shoes, and levers. Has anyone else tried that? Success? Failure? Seems plausible (it works on the prototype), but does it translate to the model?
Later,
K
