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Straight modules must be built in one-foot length increments. Recommended: Straight modules should be built in two-foot increments; if you build an odd-length module, you should build a pair of them so the total length is a multiple of two feet.
Recommended: on the "standard" straight module, the front mainline is 2.50" from the front, and the overall depth of the module is either one or two feet (plus the thickness of the skyboard, if any).
Offset modules are the same as straight modules, except that the interfaces may be offset from each other (but must still be parallel). Recommended: Unless the module is being built for a specific geometry-matching need, the offset should be a multiple of one foot.
Recommended: there are four different "standard" corners, described in Appendix A. The 24-inch corners are the smallest corners that meet the minimum-radius standards, and fit nicely with available lumber sizes. The 27-inch corners are based on a 24-inch "track grid," and work well for complex layout geometries.
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.
Please note that 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.
Module legs must permit the height of the module, from floor to top of rail, to be continuously adjustable between 39.00" and 41.00". The nominal height of a Smart-N module is 40.00".
Although it may seem natural to put legs at the extreme ends of a module, care should be taken to keep the legs from interfering with the clamping space required at interfaces.
All S-curve situations on the mainline must incorporate at least 4.90" of tangent (straight) track between the curves.
Any crossing of the mainline at an angle less than 10 degrees must use a "movable-point" crossing or double-slip switch. Gantlet track is not permitted on the mainline.
Parallel track centerlines on straight mainline track must be at least 1.20" apart. Recommended: Parallel mainline tracks will usually be on 1.25" centers.
Parallel track centerlines on curved mainline track must be at least 1.50" apart. Recommended: On curves of 90 degrees or less, this can be accomplished by using the same radius on the "outside" track as on the "inside" track, and offsetting the center of the curve to compensate. On curves of more than 90 degrees, the outside track could be on the same center as the inside track but with a 1.50"-greater radius, and offset curves used at both ends to transition from the tighter parallel-track spacing.
The interface side(s) of a module must be at least 6.00" wide. Recommended: the "standard" modules are designed with 12.00" or 24.00"-wide interfaces.
The total height of the interface, from top of railhead to bottom of frame, must be between 3.75" and 4.50". The height of the framing at the interface must be at least 1.50"; the thickness must be between 0.50" and 1.00". (This is to ensure that modules can be clamped together.) Nothing may extend beyond the plane of the interface. Recommended: Most modules will probably have a 1x4 board (nominal; approximately 0.75"x3.50" actual) for the frame, with a .25" or .50" plywood top and cork roadbed under the mainline track.
At each interface, there must be two mainline tracks. The mainline tracks must end between 2.47" and 2.50" from the interface. At this point, the centerlines of the two tracks must be 1.25" apart, and the direction of travel must be perpendicular to the interface. If the mainline is set on roadbed, the roadbed must continue straight from the end of track to the interface.
The centerline of a mainline track must never be less than 2.25" from any unprotected edge of the module. An interface is considered protected when attached to another module. Other edges may be protected by placing obstructions between the edge and the mainline. These obstructions must extend at least .50" above the railhead, and must be sufficiently "solid" so that a standard-height boxcar cannot pass through any gaps.
The centerline of a mainline track must never be more than 24.00" from the nearest accessible edge. Any tunnel or similar situation over 6.00" long must incorporate a means of ready access to the track.
Each interface must have four spring or European-style block connectors for connecting 22-gauge wire, arranged in a straight line to form a "connector block." Recommended: Radio Shack has spring-loaded, stereo speaker connectors that are ideal for this purpose.
The connector block must be parallel to and within 2.50" of the interface, arranged horizontally so that the relative positions of the four connectors correspond to the positions of the four mainline rails. All connectors must be within 2.00" of their corresponding rail (or the continuation of that rail to the interface). Recommended: The connector block will usually be on the inside of the frame at the interface.
All mainline wire junctions must be either soldered and insulated, or screwed together on a barrier strip.
All switches used in mainline wiring must be visible and accessible to a standing or seated operator.
Mainline tracks must be electrically isolated from each other. This will usually be required at mainline crossovers, or on balloon modules.
Non-mainline track must be electrically isolated from mainline track.
On corner modules, junction modules, and straight or combination modules with more than three feet of mainline distance between the interfaces, the interfaces must be electrically isolated from each other.
Each mainline track connecting two interfaces must be accompanied by a double-pole switch that can be used to override the isolation between the interfaces for that track (if such an isolation exists).
If there are mainline track sections that are isolated from all interfaces, a double-pole switch must be used to allow the section to be connected to an interface. (There can be no "dead spots" on the mainline that cannot receive mainline power.) Recommended: if two switches are used, one for the interface at either end, then the section can be "reassigned" between the two interfaces and becomes quite handy for dispatching purposes.
It is possible to design Smart-N modules that also interface to other N-scale modular standards (NTrak, Bend-Trak, etc.). Such interfaces are beyond the scope of these standards.
If a skyboard is used, it must not exceed 12.00" in height above the lowest mainline trackage on the module. Recommended: most skyboards will be made of 12.00"-wide material, which will then be overlapped with the back of the frame, resulting in a skyboard height of 8-9 inches.
All cut-off scenic features (mountains, streams, etc.), on any side of the module, must present a flat surface along the plane of the cut. If this surface will be visible from the normal viewing direction, it must be painted matte black. Recommended: all visible portions of the frame should also be painted matte black, to avoid drawing attention to the cutoff.
All modules should have at least basic scenery completed. At least grass...
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