Wayne Roderick, 3rd Division, PNR, NMRA (life)

10/27/00 rev 02/12/09

The double ended holding and staging yards at Offline, OFL is generally presented at THUNDER MOUNTAIN and the OFFLINE HOLDING YARDS. It would be a good idea to go there first for the bigger picture and I'm taking that for granted. Here we are going to get into the nitty-gritty of how to take a simple track laying project and make a monster of it (grin).

Since operating on Lee Nicholas Utah Colorado Western, I became convinced that I needed a much better staging system so we could use and enjoy the collection of locomotives and cars that accumulate over the years and at the same time extend the enjoyment of operations with much greater variety. This means we have to have a quick and easy way to move rolling stock on to and off of the railroad and fit it all in with the scheme of operations.

Here, I will explain the mechanics of the NEW staging yards at OFL. You've seen the photos on the page that linked you here, so now we'll give you some sketchs and drawings.

First, we need a readily accessible storage system for cars & locos that are beyond the capacity of the TSL trackage. We can only accomadate about 150 freight cars on the TSL tracks and the inventory, after umpteen years in the hobby, is far more than that. To satisfy that, I have assembled 30 drawers in a 5 wide by 6 high configuration just under the staging yard. Each 14" x 16" drawer holds enough cars to make up a typical train size for the TSL. Others are used for locos. The new eight track lower yard replacing the old five track lower yard is only 32" from the floor, the lowest track elevation on the TSL, so it is convenient to wheel around in an office chair. Four of the eight tracks in the rear are under the upper OFL yard with only 4-1/2 inches clearance and are used for holding only. Because this new LOWER OFL yard is wider than the UPPER OFL yard, the remaining tracks are readily accessible. Track four is the MAIN for through traffice and tracks one, two and three are for staging. Extra re-railers are provided for quick railing of cars. The upper OFL holding yard is unchanged in the project except for the new control panel and circuitry.

New switches are handlaid with code 70 and 83 on PC ties. No great attempt is made for detailed scenery as this is designed for function, not beauty. The bulk of the trackage is simply Atlas code 100. Why the smaller rail for switches? It's easier to work with and I had it.

At this point we could keep it simple with ground throws on the twenty-five switches in the upper and lower yards, but what's the fun in doing it simple when you can make a real project out of it? Besides, I need some way to switch power in the frogs- No,I don't do dead frogs! If you've stayed with me this far, then let's see just what we can do to optimize the control scheme.

How many switch machines? Well 25 switches suggest 25 machines- NO WAY! If I want to select one of eight tracks, I only need three machines. It's one of those binary things. The Tortoise machines have plenty enough muscle to move four switches, you just need to use a little music wire, and maybe a model airplane bell crank along with some solder to glue it together. Three more on the other end of the yard and we're done. They work in pairs, so I only need three functions to work them. Because the upper yard has five tracks, I need another group of six for it. One end of my new yard has two in/out routes so I need another. The count is up to 13. Sure saves a lot of money. I'm using the Tortoise machine, it's the best thing to come along since I built my own slow motion machines in 1975 (still in service too). With two double throw sets of contacts, the paired machines eliminate any need for additional relay switching to keep all frogs powered.

click on the thumbnail for a bigger, VGA size picture


This is the big picture showing track and switch machine wiring, even at VGA resolution it may not be adequate. If you really want to get into it, ask and I'll send you an ACAD.DWG file. The first thing to notice is that only one track in each yard has is shown with a red AND cyan rail. All the others are electrically dead until aligned. This is the old selective turnout trick taken to it's extreme. Not too important today if you use DCC but it avoided having to have track power switches for each track. Our panel controls switch machines only.

I've developed a little wisdom in the years and one of the more important items is: build it on the bench rather than on your back. The ladder tracks with the switches are built on removable pieces of 5/8" chipboard complete with plug-in connections. The eight foot of simple trackage between the ladders has no wiring. That's right- there is enough redundant connections with rail joiners to make that work providing you use good mechanical techniques (file a gentle taper on your rail ends so you don't ruin the tight fit!) I use six inch bridging tracks across the module joints to insure a smooth transition. At the bottom of the drawing, you'll see how the Tortoise contacts are used for hot frogs in the four usable configurations of the double crossover.


Further, use of the Tortoise contacts let us align each yard with the track polarity that it feeds from or feeds to. Somewhere, of course, we're going to have to switch polarity, if we are to turn a train from Eastbound to Westbound or vice versa. That is done while a train is in the Thunder Mountain Loop. How we done it has varied over the years while running with primitive analog power. Today, most DCC users opt for the automatic gadget that swaps polarity when a short is created at a rail gap. I don't accept this brute force method for a number of good technical reasons so we set the loop polarity to match the upper OR lower yard when the train APPROACHS the gap. This is done with optical sensing.

panel We have the track and switch machine linkage built, now how do we present a friendly interface to the humans? If you are here, you know what Graphical User Interface, GUI is all about. We look at the picture and without further instructions, do the logical thing and that's what this panel is all about. No wiring diagram either- Don't need one, just the few words in the drawing. Everywhere on the TSL, an electrical device whether operated by human, robots or computer is actuated by sinking it to ground if possible.

Stamp ucontrol Finally we have reached the core of the system where the GUI meets the rails. The switch machine pairs are wired in series. The standard 12 volt buss on the TSL is quite enough to move two machines each of which may move up to four switches with appropriate mechanical linkage. I use a Norton op-amp, LM3900, but there are lots of them that will do the job such as the LM339 that we use in the DCC booster, to drive the machines. Five volt, TTL logic level signals from the controller drive the op-amps. Two DPDT relays for polarity control are interfaced the same way. This is basics and not shown here. The controller is a Parallax Basic Stamp II (really it's a clone but works the same). The controller is assembled on a piece of .01" spaced perfboard cemented to part of a salvaged 22pin circuit card (cheap!) so it can fit a common 22 pin jack. The Inputs and outputs use a salvaged 25 pair telephone plug/jack that was used by the millions for common 6-button office phones. By using serial I/O chips 74x164 and 74x165 chips I have 48 I/O connections with leftovers for future interface with whatever may come along such as automatic traffic generation by the computer. If you really want to learn some of the details and you have the time for a big download then CLICK HERE for a high rez picture and then come back and CLICK HERE for the actual BS2 code You can read it easily with any text editor. The Parallax Basic StampII is a great little tool for model railroad applications like this. It's very easy to work with and the friendly Basic programming is easily learned by most anyone.

Yes- I have an embedded computer on the TSL that could do this, butbut I've been holding off while seeking a good Layout Control Bus (LCB) This little gadget seemed like a good way to handle the yard logic until the LCB standard is firmed up Did you look at the BS2 controlling our rotary dumper ?

01/02/04 I have adopted Bruce Chubbs CMRI as my Layout Control Bus (LCB). Today it would be a simple task to use one of his SMINI cards with 24 INs and 48 OUTs to control this whole mess.

02/07/04 It's hard to leave things alone. I wanted to make a couple small changes and it would involve wiring and redoing the Parallax code. Instead I just ran the INPUT and OUTPUT wires into our CMRI system and added a few lines of Quick-Basic code to the embedded program. The Parallax project was fun, but with CMRI so easy to work with, it was an orphan. It's gone.

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