Compact yard throat

[lionelsoni]

I just finished my new O27 yard throat, which is unusually compact. I thought I would try to describe it here for anyone who can use the idea. The yard is along one side of the room and the yard lead is across the adjoining side; so the throat fits into the corner between them, and a train entering the yard changes direction by 90 degrees. The throat uses only 28 inches in O27 and has the unusual property of not getting any longer as you add yard tracks.

As you face the corner, the lead is on the right and the yard on the left. The lead becomes a ladder track, with a left-hand switch every 11.5 inches. This requires a 2.661-inch straight track between switches. Each ladder-track switch leads eventually to 4 yard tracks. The last ladder-track switch is replaced by a simple 45-degree left turn.

Each ladder-track switch connects directly to another left-hand switch. Each of these intermediate switches has a .498-inch straight section on its non-diverging outlet, followed by a 30-degree left turn. On the diverging outlet, there is a .131-inch straight section, then a 15-degree right turn. (These straight sections are so short that I simply cut the turns long by the small amount needed.)

After that, each track goes into a final switch, which is a left-hand switch cut down to a 30-degree diverging turn and a 7.817-inch straight. The diverging outlet goes to a 15-degree right turn and the non-diverging to a 15-degree left turn. (The diverging outlet is 1.08 inches shorter than the non-diverging, so the yard-track lengths differ by that much.) The yard tracks are 2.875-inches apart on centers, which is my standard spacing.

Of course, this design can be made in a mirror image, with right-hand switches. It should also be possible to scale it up for O31. I will have to leave the housings off the Lionel switch machines of the final switches.

[Frank53]

Bob - a heckuva description, But I am not saavy enough to follow all that thinking. ANy chance you have a sketch or photo?

[lionelsoni]

I know that would be easier to understand; but I'm afraid I haven't a clue how to do it. Perhaps someone can help out by making a drawing from my description.

[Frank53]

Bob:

ok, I read it very slowly, and kinda, sorta get it. What radius are the switches?. and it strikes me the bulk of the switch could be the big stumbling block (at least for me) in o-31.

It appears the yard has 12 legs and takes 10? switches?

[cnw1995]

Wow, I can't believe this is so compact. I've wanted to do something like this but the space between yard tracks and the switches was (relatively) gigantic. I didn't think to use smaller pieces of track - you cut them yourself, didn't you?

[lionelsoni]

Frank, they're all Lionel 5121 O27 switches. The number of switches is one less than the number of yard tracks. In my case, that's 7 switches and 8 tracks.

I think it might scale up to O31. Everything would be larger, of course, with the track spacing about 3 1/4 inches instead of 2 7/8. This makes more room for the switch machines. Also, the final switches are canted at 15 degrees to the yard tracks; so there's a good chance that the machine of one switch can fit behind the next switch. Another possibility in O31 is to use the three-piece switches that Lionel made for a while. Their curve might be exactly the 30 degrees needed, which would save a lot of work cutting down a normal switch.

Doug, yes, I cut a bunch of track and, of course, half of the switches. If you want to try this, I can give you some tips to avoid having to repeat my mistakes.

I also added a microswitch to each switch to route track power to only one of its outlets. That way, only the track that the switches are lined for has power. I disconnected the anti-derailing feature, since a train can't move on a track for which the switches are not lined. I will be adding a diode matrix for throwing switches, which allows me to use only 4 controllers to line the switches for my 8 tracks.

[FJ and G]

Bob,

Is this the "pinwheel" yard that was described in the 2005 Track Planning magazine (put out by Kalmbach)?

If so, I believe that the space saving results from the ladder peeling out from the curve, thus the term "pinwheel."

To visualize the pinwheel effect, think of the letter E or F. The horizontal lines in those letters are the ladder tracks (of course there would be a lot more) shooting off from the vertical mainline as it makes a right-hand turn.

I'm I describing it correctly?

[FJ and G]

BTW, the other advantage to the pinwheel is that not only are you saving space, you also are avoiding the dreaded S curve effect that you get on the first "rung" of a ladder.

[lionelsoni]

Dave, I'm not familiar with that magazine nor the "pinwheel" name. But it sounds like the ladder track uses the same concept. However, my ladder doesn't go directly to the yard tracks, since that would space them pretty far apart. Instead each rung of the ladder divides and subdivides to 4 yard tracks. Unfortunately, this does result in some wiggles, but smaller ones than you would get with 45-degree turns.