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This is a companion document to the Smart-N Module Standards. In this guide, you will find examples of module designs that meet the Smart-N standard.
The Smart-N standard is maintained by the Meade Area Railroad Society (MARRS), of Laurel, MD. As of the date of this document, the MARRS web site is located at http://www.marrsweb.org.
A single module may be composed of multiple, module-like sections that are designed to always be used together. On such a module, the "internal" interfaces between the sections are not required to meet the interface standards.
When possible, it's good to use at least a short piece of sectional track, or a turnout, as the first piece of track directly off an interface. This area is subject to high amounts of stress, and the rigid sections of sectional track hold their shape better under stress. Also, if damage occurs, it's easier to replace a piece of sectional track than to try to trim flextrack to precisely replace the damaged portion.
Straight modules have two parallel module-to-module interfaces,
connected by two continuous mainlines. The interfaces must not
be offset from each other; that is, regardless of what curves occur
within the module, the geometry of the interfaces
must be as if the mainlines were perfectly straight.
The basic straight module is a rectangle. The illustration shows a typical 4-foot-long module. While 4- and 6- foot lengths are most common, 2-footers are not unheard of. 8-footers are rare because they are difficult to transport. Odd lengths are not illegal, but are discouraged, to simplify layout planning.
Most straight modules are 12" or 24" deep, with 18" in occasional use. Modules over 24" deep are discouraged, since they could interfere with other modules if placed near a corner.
At the interfaces, the mainline centerlines are 2.50" and 3.75" from the front of the
module. While the mainlines can curve within the module, they need to come back to
these distances at the interfaces (otherwise it's an offset module, not a straight).
If a straight module is going to extend out in front of the "standard" modules, it's recommended that the protruding corners be "knocked back" at an angle of 30 or 45 degrees from the interface. (30 degrees is roughly a 1-to-2 ratio, while 45 degrees is 1-to-1.) The angle makes the front edge of the layout look more finished, and reduces the probability of someone bumping into a sharp corner and damaging either themselves or the layout.
Note that a forward extension of a straight module doesn't count against
the 24-inch maximum recommended depth.
Offset modules are similar to straight modules, except that the interfaces may be offset from each other (but must still be parallel).
This sort of geometry-matching module is common in
some modular systems, but is seldom needed in Smart-N, except for
visual effect in a particular situation.
Corner modules have two module-to-module interfaces at 90 degrees to each other, connected by two continuous mainlines.
This is the most common corner in use with Smart-N, and can be built on the pre-cut 2x2-foot plywood sheets available at most home centers.
(The desire for a two-foot corner module was the primary factor behind Smart-N's
17-inch minimum radius. To fit a double-track corner on a two-foot module,
with easements, a 17.25-inch radius was the largest that could be used
for the inside track.)
The track geometry of this corner is identical to the standard two-foot
corner. The only difference is that the edges of the module are cut on
curves, to maintain the 2.50" spacing for a module "front" on either side
of the tracks.
This is the alternate "standard" corner used by MARRS. By making the corner
three inches larger, the interfaces are positioned 24 inches apart horizontally
and vertically. This "grid-aligned" geometry could potentially simplify
the design of complex module arrangements involving
concave ("inside") corners, double-ended branches, and the like.
This design takes advantage of the slightly larger size of the "grid" corner
to slightly increase the radius of the curves on the module. Theoretically, the
radii could be increased a bit more, but that would involve exposing flextrack
to damage at the interface.
Junction modules have three or more module-to-module interfaces. Two of the interfaces are placed and connected to correspond to a straight, offset, or corner module. Each additional interface on the module must connect to at least one of the first two interfaces.
Named after early design sketches that resembled a Japanese throwing star, the shuriken is the answer to the question, "what can we do with an extra loop module?" The shuriken can serve as a standard corner module, or it can be used to "throw" the main line off the corner and toward another end loop, allowing module arrangements beyond the simple loop-to-loop.
Though the shuriken resembles a wye at first glance, it isn't a true wye, since it can't be used to turn trains. It would need the help of a crossover somewhere along the diagonal "arm" of the layout to perform that function.
This is the tightest loop that can be made and still meet the Smart-N standards for minimum radius, easements, and S-curves. (Well, in theory, it could be 0.15" shorter.) In order to make the module as small as possible, the mainline comes within one inch of the edge at three points, which means these points need some form of edge protection to meet the standards.
The first module that was built to this design was actually built in
two sections, each 51" by 18.25". By adding the extra 0.5" of overall width,
the 15-degree section of the loop that crosses the joint between the sections can
be replaced by a 19-inch radius "joiner" piece of sectional track, without disrupting the
track geometry.
Combination modules are single modules that replace a combination of other modules. For
example, a combination module might be a "drop-in replacement" for a two-foot straight
module, a 24 inch corner, and another two-foot straight module.
Special modules have one or more module-to-module interfaces, and do not match any of the
preceding descriptions, due either to the position of the interfaces or the connections between
them. Recommended: Special modules should not be built except to meet a specific need.
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