N Scale SIG Module Specifications of the
Boulder Model Railroad Club
Last Modified On: Monday, 07-Aug-2000 20:46:58
N SCALE "LOW-TECH" MODULAR
By the N-SIG of the
BOULDER MODEL RAILROAD CLUB
This is a guide book, not a rule book.
Why are we doing this anyway?
Building what used to be called benchwork.
Or track fun, depending on your point of view.
How we get 'em to run.
Thoughts and ideas.
View (17 Kbytes)
Diagram (Molex) (20 Kbytes)
Diagram (Automotive) (121 Kbytes)
to Automotive Conversion (121 Kbytes)
- Corner Module
- Switching Module
"I think you're going to like this," a friend told
me one day over lunch. "A few people from the Boulder Model
Railroad Club are starting an N-scale modular group and their
approach is very appealing. The idea is to have as few rules as
possible and let everyone do their own thing."
It sounded interesting, controlled anarchy. I liked it
already. It got better, my friend told me. "Another concept
of this group is to make everything about the modules very
"low-tech"; make them really easy to build. For
instance, the base will be made of foam building insulation
board, so that an hour after you get the urge to build a module,
you can be done with the base and ready for the fun stuff: track
and scenery. And instead of building legs onto the module, we'll
just set the foam base on folding tables to set up for a
This was also a winner for me. I've seen a lot of layouts that
got bogged down at the benchwork stage because the builder really
wanted to jump right into the creative, fun stage of creating the
railroad, but ended up in an elaborate engineering project that
was more like work than play.
"The approach to track," he continued, "is to
model the most commonly seen track configurations in the real
world. That means there'll be a backdrop down the middle of the
module with a single track on one side and a double track on the
Once again, I liked the approach. This arrangement of track
would allow me to model the aspects of railroading that are
interesting to me; a single track mainline running through the
mountains on one side, and a passing siding or an urban switching
area on the double track side. With each successive idea I found
myself being drawn into this concept more and more.
"A side benefit of having this arrangement," my
friend elaborated, "with the backdrop running down the
middle of the modules, is that it gets the operators out with the
public at shows, instead of back inside the layout. This makes it
easier for people to ask questions and meet the builders of the
railroad. The end modules are loops connecting the two sides of
the modules. This has the benefit of allowing the modeler to
build the module to any length, whatever fits your scenic
requirements, or the size of your car's trunk. Also, any number
of people can join up their modules at a show without worrying
about getting the right number of modules on each side of a
This idea was incredibly simple; just right for me.
"You'll never guess how the modules are held
together." he said, smiling. "Velcro! We were meeting
at one of the member's houses trying to figure out how to connect
them when the host's wife asked why we didn't just use Velcro. At
first we all looked at her a little funny, and then we realized
that it was a great idea."
This was very ingenious, I thought. Like everything about the
modules, it's easy, fast, and low cost. This concept of
"low-tech" was sounding better and better. My friend
continued his explanation. "The Velcro holds the modules
together, and a Masonite fascia board that overlaps one end of
the module on each side keeps them in alignment.
"One of the guys built the first module in two hours and
another one added scenery to it in another couple of hours so
we'd have a prototype to work with, and also to show people just
how fast and easy this system really is. Since then members have
built a number of modules including end loops and there are more
on the way. After doing a few we've found that setting up for
shows only takes about thirty minutes before we're off and
The next Sunday afternoon I was in the mood to have some fun,
and I had a few hours, so I decided to try building one of these
modules. Including my trip to the lumber yard, I was finished
with my blue foam base in two hours, and I was only into the
project for about fifteen dollars, with enough material left over
to build another four foot module or share it with a friend.
Since I'd finished the base so quickly, I decided to start on
the scenery. Cutting the river into the foam was simple and took
very little time. I just carved out what I wanted until I was
happy with the result, and if I carved away too much, I just
glued some foam back on.
I loved the way I didn't have to plan too much in advance; I
had an idea of what I wanted it to look like, and then I just cut
away at it with a serrated knife and a Stanley Surform tool. I
had to admit, I was having a lot of fun!
Guidelines for building what used to be
- While almost any material could be used for the base of
the module, the blue (or pink, or green) Styrofoam, which
is extruded high-density rigid insulation, has many
advantages. (Note that this is not the white
beadboard insulation, which has no structural integrity.)
- It is lightweight, making it easy to transport
- It is easy to carve and shape for scenic contours
- It is inexpensive, and comes ready to use in the
2'-0" module width
- Making changes later is also easy, whether
carving it away to add an electrical switch, or
changing the scenery
For cutting the foam board to size use any tool that
cuts wood, a basic hand saw works well. For gluing foam
to foam you must use a compatible adhesive such as water-based
(latex) contact cement, rubber cement (used as a contact
adhesive), or a construction adhesive that's made for use
with foam such as PL-300. Just don't use
solvent-based glues, they'll melt the foam. For
gluing the Masonite and the cork roadbed to the foam you
can use wood or craft glues such as Elmer's or TiteBond
(note: these wood glues require air to dry so they can't
be used to glue foam to foam, no air gets into the
- The modules are all 2'-0" wide (except the end
loops) but may be any length you want. 4.9" (the
length of the bridge track) is the shortest, and
8'-0" is probably the longest practical size, but
anything in between is fine (see the drawings at the end
of this guide).
- The single track mainline is 1" higher in elevation
than the double track mainline. To build up this
additional elevation its easiest to simply stack a layer
of 1" thick foam on top of the base layer. Be sure
to use a foam compatible glue.
- The modules are set on folding "banquet" tables
for display at public shows so they don't require any
legs of their own. If the scenery of any module drops
below the base of the module, then the tables are simply
spaced apart at that point. The module itself must be
able to span this gap between tables.
- The sky backdrop is made from 1/4" thick
"Foamcore", a white paper-faced foam panel
available from art supply stores or
"Gatorboard", a plastic-faced foam panel. It
runs the length of the module, separating it into a
16" deep scene on the double track side and an
8" deep scene on the single track side.
- The front faces of the module are made from 1/8"
thick tempered Masonite hardboard. This durable material
supports the foam module base up off the table, allowing
space for electrical wiring to run below. The Masonite is
also offset 1/4 inch at the ends as a means to align the
modules with each other (see drawings at the end of this
- To fasten adjoining modules together, a 4 1/2" long
strip of Velcro "hook" strip is fastened to
squares of Velcro "loop" that are attached to
each end of the module faces (see the drawings at the end
of this guide). You will need 2 strips of hook material.
Or track fun, depending on your viewpoint.
- Except at the interface at the ends of the modules, the
track configuration can be almost anything you want. The
only constraint is that the minimum radius for the
mainline tracks is 20". See the drawings at the end
of this guide for track centerline locations and
alignments at the ends of the modules.
- Before the track goes down we need some roadbed to put it
on. Standard 1/8" thick N scale cork roadbed like
that made by Midwest works just fine for our modules. It
comes as a strip that has been slit down the middle. Just
separate the two halves and glue the square edges
together along the track center lines.
- Mainline tracks can be any manufacturer you want. Minimum
flextrack rail size is Code 55 which allows most
equipment to run on it. At each end of the module the
rail size must transition to Code 80 to mate with the
connector or "bridge" track.
- Each end of the module must have a removable connector
track to bridge the joint between modules. Use a standard
Atlas 4.9" straight track (Code 80 rail) for this.
You will need 3, one for each mainline track. Since these
bridge tracks are 4.9" long, the ends of the
mainline track rails must be held back from the foam ends
of the module exactly half that length (see the drawings
at the end if this guide). Be sure to cut back the ties
on the mainline tracks to allow for the rail joiners. The
mainline tracks should be straight for the first inch or
so, so there won't be a kink where the bridge track
- Any turnout (track switch) on the mainline tracks must
have a live metal frog and positive acting points.
Turnouts used between mainline tracks should be number 8
or larger. All other turnouts and for that matter all
track that is not part of the mainline can be any size
and configuration you choose.
- Gaps must be cut in the rails in several locations to
prevent shorts and to create "kill" sections of
track. The kill sections are created by cutting the back
rail of each mainline track a few inches from each end of
the module (see the wiring diagram at the end of this
guide). Other gap locations are: both rails on branches
off of the mainlines, both rails on crossovers between
the mainlines, and the rails that diverge out of all live
metal frogs. Of course all of the resulting rail sections
must have power feeders - see the "Electrical"
How we get 'em to run.
- Refer to the wiring diagram at the end of this guide. Note:
All electrical connections must be soldered. The
modules get moved and bumped so any other type of
connection can become loose over time.
- Each module has an eight wire electrical "bus"
running the length of the module below the foam base.
There is a lot of flexibility in what connectors to use
for wiring modules together. Our first attempt used 9 pin
Molex plugs, but we found that they were hard to plug and
unplug and the pins tended to pull out. We are now
converting over to 4 pin automotive plugs, designed for
being hooked and unhooked. Both schemes are described
below. These schemes are incompatible (however, we
have a conversion diagram), so decide on one scheme
and use it consistently!
- The bus wires must be 18 gauge or heavier
(smaller gauge number) stranded wire, and must be
6" longer than the module on each end.
- The bus has Molex plug connectors at each end.
These are available from Radio Shack:
Shack #274-229 9-pin male connector at the right
Radio Shack #274-239 9-pin female connector at
the left end*
* when viewed from the double track
- The bus wires to Molex pins #1 through #6 are for
track power. There is no bus wire #7 so Molex pin
#7 is unused. Pin/bus wires #8 and #9 are used
for accessory power such as building lights. All
of the pins must be soldered, not crimped. Make
sure to put the right pin in the right hole and
use care in installing them into the plastic plug
housings since the can only be removed with a
- The bus wires must be 18 gauge or heavier
(smaller gauge number) stranded wire, and must be
6" longer than the module on each end.
- The bus has automotive connectors at each end.
These are available from auto parts stores and
Radio Shack (#270-027). They are used for
connecting trailer lights and other accessories
to a vehicle. They are polarized and intended for
quick connect and disconnect, yet are weather
resistant. When viewed from the double track
("front") side, the "female"
(1 pin, 3 socket) connector is at the left side
and the "male" (1 socket, 3 pin)
connector is at the right side.
- The bus wires to the double track side go to one
pair of conductors and the bus wires to the
single track side go to the other pair,
distributing the power between the two pair. Make
sure to attach the right feeder wire to the right
- A "kill" switch for each mainline track (ie: 3
switches) should be installed in the Masonite fascia
boards. This allows a section of track to be turned off
in an emergency and can be used to regulate the spacing
of trains when several are being run at once. The
following conventions for switch location and wiring are
used so that all modules are the same and in an emergency
anyone can use the kill switches without having to figure
out how they work first.
- The kill switches need only be single pole single
throw (SPST) toggle switches.
"Sub-miniature" switches such as Radio
Shack #275-624 or #275-634 are fine. Push button
switches should not be used since their use can
cause the lightweight modules to be pushed out of
- The kill switches should be mounted near the
center of the Masonite fascia board such that
toggle up is on and toggle down is off. The
switches on the double track side should be
mounted one above the other. The one on top is
for the back track and the one below is for the
- (Molex) The kill switches get wired between bus
wires #2, #4, & #5 and rails #2, #4, & #5
(see item 5A below).
- (Automotive) The kill switches get wired between
the brown and green bus wires and rails #2, #4,
& #5 (see item 5B below)
- Track gapping to form separate electrical blocks is only
required in a few places - see item 6 under Trackwork.
- Track wiring:
- (Molex) The "front" of the module is
the double track side. The closest rail (the
front rail of the front track) is wired to Molex
pin/bus wire #1; the next rail back is wired to
bus wire #2; and so on back to the farthest rail
(the rail closest to the face on the single track
side) which is wired to bus wire #6. Don't forget
those kill switches.
- (Automotive) The "front" of the module
is the double track side. The closest rail (the
front rail of the front track) and the front rail
on the second track is wired to the single pin on
the "female" connector; the next rail
back and its equivalent on the second track is
wired to the socket next to the pin on the
"female" connector; the rails on the
single track are reversed - rail #5 is wired to
the other conductor on the edge of the connector
and rail #6 is wired to the inner conductor.
Don't forget those kill switches.
- Each piece of rail should have its own feeder
wire soldered to it. Don't rely on rail joiners
to conduct electricity, even if they're soldered.
This also applies to each piece of rail in
turnouts; they should have individual feeders
- Track feeder wires may be 26 gauge solid wire if
they're short (4" or so). If the feeders are
longer, they should be heavier gauge wire.
- Other Wiring (Molex):
- The power pack must connect to the modules at
some point. Since the end loops are always used,
they are the best place to have a connection
strip. We've also found that a connection point
is good at a corner module (if you have any). At
this point Molex bus wires 1, 3, and 6 tie
together and wires 2, 4, and 5 tie together
forming the two track feeder connections. Bus
wires 8 and 9 should also have connection
terminals for lights and switch machines.
- Turnouts (track switches) can be manually or
electrically operated. For electrically operated
switch machines power comes from bus wires #8 and
#9. These two wires are connected to the constant
D.C. voltage of the power pack. This varies from
pack to pack but is usually 12 to 18 volts.
- Lighting for structures and other things on the
modules can also be fed from bus wires #8 and #9.
Just be careful that your miniature bulbs are
rated for the voltage.
- There is no wire to terminal #7 on the Molex
plugs. Its just extra.
- Other Wiring (Automotive): Each outer automotive
conductor ties not to the conductor next to it (for that
would create a short circuit, but to the the one after
that. There is no auxilary power bus, so lights, track
switches, etc. will need their own power feeds.
Thoughts and Ideas
Working with foam insulation board as our
module base has many advantages when it comes to creating
- Its so easy to carve and shape contours that you can
create finished scenery in a very short time. A serrated
kitchen knife and a curved Stanley "Surform"
tool are among the easiest ways to carve and shape basic
contours. Final smoothing and blending is quickly done
using 60 or 80 grit sandpaper.
- To color your foam "ground" any latex house
paint works well to provide a basic earth color, or you
can use any plastic compatible hobby paint.
- For scenic texturing and ground cover most traditional
methods work well, just avoid anything with a solvent
base. The book How to Build Realistic Model
Railroad Scenery by Dave Frary form Kalmbach
Publishing is an excellent guide to water-based scenery.
One of the reasons to build a FoamRail module is to connect up
with other modelers at public shows. Other than making sure there
are a couple of end loops and some folding tables to put
everything on, the coordination is pretty simple. Just take along
a few things:
- Your module.
- 3 bridge tracks with rail joiners.
- 2 strips of Velcro.
- Some scrap Foamcore board and shirt cardboard along with
a knife or scissors to cut it. This is to shim the
folding tables (and the occasional wayward module);
remember, these tables are our foundation benchwork, so
they need to be level even if the floor isn't.
- A power pack. We frequently find ourselves running 4 or 5
trains with multiple locomotives simultaneously, so a
pack with at least 2.5 amp rating is recommended.
- Some stanchions and rope to create an operating aisle
around the layout and to keep little fingers from helping
the trains along.
- And last, but not least, some locomotives and rolling
stock. Have fun!
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