San Diego Model Railroad Association
HO Layout Construction Details

The Association predecessor, the San Diego Model Railroad Club, became one of the charter members of the San Diego Model Railroad Museum in 1980, and planning began on permanent layouts. The new HO layout was planned to include:

See the initial design criteria in the standards section of this web site.

Construction began in April 1982 at the peninsula containing Coyote Wells and Plaster City. By this time the logging branch had faded from the plans, and the minimum radius was the norm. Construction using flex track on homasote over laminated spline sub-roadbed built from Coyote Wells to the Hipass wye by 1984. In the next year track reached Valle Redondo and a temporary loop. What looked fine on paper was turning out to not be operationally sound. By 1990 large portions of the mainline had been redesigned to increase the radius and improve the grade. At the formation of the Association, 99 percent of the track work is complete.


From the outset, benchwork has been constructed from member-built I-beams. Lighter and stronger than L-girder construction, I-beams are versatile enough to build complex shapes quickly. Sub-roadbed began as laminated spline, but this was later abandoned in favor of cookie-cutter 3/4 inch plywood. Likewise, the homasote roadbed proved undesireable in the San Diego 15% to 99% humidity levels. Only a tiny fraction of original roadbed and flex track exists. Today 5/16" pine strips are nailed and glued to the plywood, then planed smooth in preparation for wood profile ties. Visible track is mostly hand-laid code 100, with some code 83, on the standard gauge. Code 70 is used for the narrow gauge and dual gauge section. The larger rail sizes have been helpful extending rail lifetime. Operations are now 6 days a week.

As layout construction progressed, construction practices improved, and the first layers of hydrocal hardshell brought the layout to life. It is hard to imagine that those first barren tracks are now part of the rich scenic vistas you see today.


Electrical Systems

The San Diego Model Railroad Association HO layout is large and complex and operation skill levels of members and visitors cover a wide area. For these and other reasons, Digital Command Control (DCC) is used, but analog DC and block section are retained. This means there is great flexibility in operations, depending of operator desires. Usually it is all DCC or all analog DC, but it is possible to operate portions with each system simultaneously. For example, the HO main line can be DCC, but the narrow gauge analog DC.
Each control panel on the layout has at least three local DC throttles capable of sustained load up to 5 amps. Circuit breakers are provided for short circuit protection, and each throttle has meters for both voltage and current. Block selection is accomplished with toggle switch banks, with the lefthandmost active switch (if more than one toggle is "up") being the controlling throttle. In addition, the lowest priority toggle is oriented east-west (center off) and allows that block to be remoted to the next panel. Entire panels can be bypassed in this manner if short handed, or cascaded panels may be controlled from a distant location.
DC Throttles are manufactured by association members, with the heavy electronics mounted under the layout, and the hand-held controller a small, light weight, box tethered with telephone coil-cord. Failures are easily replaced with spares, and members can trouble shoot problems by swapping controllers, cords, etc. without any tools.
DCC operations use NCE command stations (a separate command station and booster is used for the programming track). Each panel has a 10 amp DCC booster, and quad power shields which divide the panel based on the same block toggle switches used on DC. When DCC is enabled, a relay panel automatically disconnects the analog DC power supplies and energizes the booster power supplies.
The layout is common rail (except the branch line and narrow gauge areas) with all buss wiring 14 AWG stranded wire. Track feeders are 20 AWG stranded, limited length. All connections use barrier strip terminal blocks and crimp terminal lugs. In line wire splices are not allowed. All wiring is color coded for easy trouble shooting.
Switch machines are PFM slow motion with feedback LED indication wiring. There are no hand-throw turnouts on the layout. We have close to 300 switch machines in daily operation, and failure rates of 1 machine every couple of years. Some gear lubrication is required periodically for heavily used switch machines.


Hardshell and Scenery

The current hardshell consists of foot long nylon stucco netting strips dipped into a thin mixture of Hydrocal, which fills the mesh holes. This is then placed on a wadded paper form and successive layers built up criss-cross to a thickness of about ½". At this time the underlying paper is removed leaving an extremely strong hardshell which is smooth on the bottom. Rock castings are then applied, and additional Hydrocal is used to form soil erosions and to fill in between rock castings. In some cases blending is performed before the Hydrocal hardens.
Cuts and blasted rock areas are generally performed using the crumpled aluminum foil method. The roughness is determined by the surrounding topography. Initial coloring is a diluted Rit fabric dye mixture sprayed on with trigger bottles. The color lightens over time, so it is hard to overdo the dye process. Foil cuts can be seen in the photo gallery at Encanto, and also at the stock pens near Valle Redondo.
Vegetation is arid or semi-arid and in photographs does not seem to be present unless extreme closeups are used. Rose Canyon is one of the few green areas, being next to the Pacific Coast. The other end of the spectrum are Carriso Gorge and the desert sands around Plaster City. El Centro greens up with irrigated fields, but fallow ground is still barren desert.


This page is under construction. Visit us again.
HO Standards HO Layout Standards page.
HO Exhibit Return To:
HO Carriso Gorge Exhibit page

 Logos copyright ©SDMRRA, NMRA