Bullfrog Mutations

I decided to use Fast Tracks Bullfrog Manual Turnout Controls for controlling the turnouts on Pembroke. I tested these out at a show a couple of years ago, and liked the positive clunk compared to some other systems. I also liked the price (you’re getting to know me by now), and finally I like the fact that they’re wood.

Being wood doesn’t only mean that these kits smell a little like my grandmother’s wood stove when you first open up the package: it also means that they’re easy to modify. Now, when you’ve got a switch throw that is about a millimetre, and the switch is near eye level, and it’s a foot away, it’s really hard to tell which way your train is going to go. So, I really want working targets on my switch stands.

To make a sane linkage between the switch and the target, I want this linkage to be below the benchwork. Otherwise, you’re trying to transform a one millimetre lateral motion into a 90 degree rotation, which implies an arm of 0.7 mm. Beneath the roadbed, on the other hand, the bottom end of a Bullfrog moves almost exactly an inch, which means you’re looking for a 0.707 inch lever to rotate the switch stand.

So, now you see the purpose of all the brass tubing on the Bullfrog in the image above. The tube coming through the benchwork is the bottom of the switch stand target, and it bends 90 degrees and connects with a loop in the end of the control rod that throws the Bullfrog. As the switch is thrown, the loop pulls the end of the target’s arm through 90 degrees. I don’t know if it matters, but you can control which direction the target moves by running the control arm through the front or the back of the Bullfrog.

The Bullfrog above is moving a target on the far side of the switch, while the one below has the target on the near side. Both will be required for Pembroke. On the near-side deployment, the control-arm has to pass through the Bullfrog from back to front, otherwise it fouls with the target itself.

When I go to deploy these for real (the one shown is a proof of concept), I will be using threaded rod for the control arm. I’ve just realized that I can use nuts on this threaded rod to precisely control the offset of the loop relative to the pivot point of the target, thereby ensuring a pretty good 90 degree rotation.

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