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Module Design

Early on, the club decided that a key goal would be construction of a modular layout so we could participate in the December, 2008, Great Train Expo.  The first several meetings therefore centered on module design.
The following specific design goals for the modules emerged from these meetings: 
  1. Develop an inclusive module specification that includes Flyer/High Rail, S-Scale, and Sn3. (Jan08)
  2. Research existing modular specifications and use this information to guide San Diego groups efforts in order to promote interoperability  among S club and NASG members. (Jan08)
  3. Module bench heights low enough for kids to see the action. (Jan08)
  4. Provision for kids to actually run some trains. (Jan08)
  5. Keep the display layout itself simple. (Feb08)
  6. Ensure that SDSG and the venue operator have a common set of expectations in advance of the event (Feb08)
  7. Ensure that staffing requirements can be met realistically by SDSG. (Feb08)
  8. Scenery should be generic enough to permit it to be attached to any linear module without an sharp visual discontinuity.(Apr08)
  9. The two mainline tracks specified in the S Mod standards should be able to be powered and operated independently. (Apr08)
  10. SDSG modules be built with either adjustable or interchangeable legs supporting both S Mod standard height and a kid-friendly height. (Apr08)
  11. Action cars and accessories should be part of the modular display. (Apr08)
  12. Control of action items should permit the visiting public, and particularly children, to interact with these items. (Apr08)
  13. Use SHS code 131 nickel-silver alloy track on all SDSG mainline tracks. (May08)
  14. Physical design of SDSG modules should promote both high portability and high flexibility in modular layout design (Jun08)
  15. Build corner modules to be reversible to promote layout design flexibility. (Jun08)
  16. Keep the amount of "tracks to nowhere" to a minimum (online discussion) 
  17. Permit easy construction of yards and trackside industries and sidings on SDSG members personal straight modules. (online discussion)
  18. Given goal 9, any interconnections between independently powered lines would have to be interlocked electrically and operationally (online discussion)
Mike Forys immediately dived into the S-Mod standard for modular layouts promulgated by the National Association of S-Gaugers (NASG).
The process of designing the modules, especially the corners, was quite an adventure!  Here is a record of the design process, including the false start that led to our final corner design.  We learned that the design of the corners is the key: with the right corner design, the possibilities are endless!  The wrong corner design, on the other hand, is extremely limiting.
Mike designed and built a first prototype corner module which he displayed at the May and June meetings:
Here's his design:

After some discussion, the club decided to increase the corner module size to conform with the Krause Corner design mentioned on the NASG's S-MODs web page. (Unfortunately, the links on the NASG site to those pages are currently broken.) This will allow us greater flexibility in layout configuration in that hopeful future when we have many modules to work with. We also agreed to build the modules as a two track standard gauge main conforming with S-MOD standards.  From that time on, Mike and Peter Gagnon collaborated in the design of the modules using the CAD program 3rdPlanIt.

The Krause Corner design enables us to construct a dogleg "L" layout by reversing a corner module.  (To help visualize this, Bob cut out some module CAD drawings and glued them on masonite blocks; we can move them around to show the various kinds of modular layouts we can create with different module designs.)
 Mike's original 40-inch square corner module wouldn't allow us to do that unless we built some small, nonstandard-size spacer modules.

Here's the CAD drawing of the Krause module we ended up with.
Click here to see a host of layouts we will eventually be able to construct as we build more modules.
Early in 2009, we began the design of a five-module rail yard that would be the big project for the year.
Click here to see more detailed drawings of the rail yard.

We quickly learned that moving trains into and out of the inner yard was difficult at best when it was powered by a conventional AC transformer, which it generally is.  Raulf donated a dual transformer to the club so the
yardmaster could operate the yard independently from operations on the mainline, and so he could hold trains on the mainline through the yard independently from operations on the rest of the layout.  This meant isolating the yard mainline electrically from the rest of the layout; an insulating track connector was installed at each end of the yard (actually one module beyond each end to give space for trains to run in and out of the yard under yardmaster control), and a 4-inch connecting cable with only a base post wire was inserted in the bus at that point.  Then we broke the mainline through the yard into two blocks so we could stop a train entering the yard while another was leaving it; both are powered by the same side of the dual transformer, but turned on or off by a toggle switch.  The yard itself was similarly broken into four blocks so we could power the whole yard from the other side of the dual transformer, but move a train in one block without moving the others.

That worked great for yard operations, but proved to be inconvenient when simply running a train around the whole layout: the train kept switching from the control of one transformer to the other as it went around the loop.  Since that is what we're doing most of the time, we needed a way to switch between single-transformer control for continuous looping and dual-transformer control for yard operations.  We installed an A-B switch on the yard control panel: in the "Local" setting, the switch feeds power from the yard side of the dual transformer to the mainline in the yard; in the "Remote" setting, it feeds power from the bus outside the yard blocks to the mainline in the yard.  In "Remote" mode, therefore, the mainline in the yard is controlled by the same power source as the rest of the layout, whether it be AC, DC, DCC, Locomatic, TMCC, or TPC.

The resulting design had an unexpected serendipity.  We had always assumed that running AC, TMCC, or TPC on the outer main would require a third transformer.  It turns out, however, that the following five-minute reconfiguration allows us to run the entire inner main on the yard transformer and the
outer main on the other one:
  1. Make sure the DCC controller is disconnected from the outer main. Connect the outer main bus connectors so the bus is continuous.

  2. Remove the 1-wire isolating bus connectors from the inner bus at both ends of the layout.

  3. Connect the mainline bus connectors from the mainline side of the transformer on the Gilbert Siding control panel to the outer main rather than the inner main.

  4. Set the switch on the yard side control panel to Local; that enables it to control all of the inner main.

  5. The outer main can run AC, TPC, or TMCC from the Gilbert Siding control panel; refer to the instructions posted on the back side of the sky board.

To return to DCC, reverse the process.

None of these considerations applies to the outer main and its yard because we generally run DCC, TMCC, or Locomatic there; engines are independently controlled under these digital control systems.  On those rare occasions where we run AC, DC, or TPC control of the outer main, we have to accept the restriction that only one engine can be on the track at a time.

Wiring of the mainline tracks on the visitor (north) side of each module (the upper side of this picture) follows the NASG S-MOD Standard.  Inter-module connectors are held in place by two cable clips when in storage or transit; we found that a single clip was inadequate.  On the west side (the right side of this picture), the red connector is male and the yellow is female.  On the east side (left), the red connector is female and the yellow male.  That allows them to be connected when in storage, and (more importantly) it prevents us from connecting modules incorrectly during setup.

Power for accessories and other tracks is provided by similar wiring on the club (south) side of the module.  To make it easy to understand, we made it consistent in style with the mainline tracks: terminal block at each end of the module and connectors between modules: use an 8-position terminal block, #16 wire, spade lugs, and inter-module connectors.  To avoid any possible confusion among connectors, however, we decided to use a 6-pin connector for this auxiliary power.  The male plug will be on the east side and the female on the west.

Barrier Strip                                                    Pin number on
Position #       Signal Name                             6-pin connector       Wire Color
      1               local module use (optional)             (none)                   red
      2               local module use (optional)             (none)                   black

      3               fixed 18V AC High                             3                       green
      4               fixed 18V AC Ret                             
4                       black
      5               fixed DC +                                        1                       orange
      6               fixed DC -                                         2                       black
      7               variable siding track power High          5                       white
      8               variable siding track power Ret           6

An example of local module use of Barrier Strip Positions 1&2 is reduced power (~12V? AC) for Gilbert accessories like the Stockyard, Guilford Station, etc. Most modules will probably not use these positions.

Modules like the Gilbert Siding and the club side of the rail yard will have a power source on positions 7&8 (connector pins 5&6) separate from the mainline to permit independent operation regardless of whether the mainline is running under AC, DC, TMCC, TPC, DCC, or Locomatic.  This is not needed on the outer main because it is designed for operation under a command control system where a separate power source is not necessary.

For modules like the new Gilbert Siding modules that have multiple accessories, lights, etc., barrier strips with more positions may be used to facilitate a larger number of connections.  Positions are marked with position number and bus wires are color-coded to eliminate confusion.

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