Module Specifications

Module Requirements

  • A module must feature one or more modular ends, modular ends come in two types – see diagram.
    • 18” wide Single track module end – Width of the modular end must be 18”, a single track must be mounted centrally (track centre line 9” from either side) at 90 degrees to the modular end and must continue for 3” straight from the module end. (The 3” of straight track ensures a short straight track between opposing curves on a main line.)
    • 20” wide Double track module end – Width of the modular end must be 20”, two tracks must be mounted at 9” from the nearest side, and 2” track centres. The tracks must be at 90 degrees to the module end and continue for 3” straight from the module end. (The double-track module end allows for longer passing sidings to be created on the single track by combining modules)

Module End Diagram:

Module end plan with dimensions

Module end plan with dimensions

  •  On double track modules with curves you may need to enlarge the spacing between tracks within the module to allow proper clearances – see NMRA standard S8  (class Ia) for reccomendations on the amount of clearance needed for large items of rolling stock on a given radius of curve. Don’t forget that you still need to allow for the 3″ of straight track at 2″ centres at each modular end though.
  • Please allow enough clearance for tall cars such as double stack container cars to use any main or through track.
  • Module-sets need to be individually self supporting and must not ‘lean’ on an adjacent module.
  • The end-piece of the module needs to be constructed with sufficient strength to accept the adjacent module being C-Clamped to it.
  • The depth of the module end must be between 3.5″ and 4.5″ deep to allow the adjacent module to be clamped to it by a standard 75mm C-Clamp.
  • At modular ends: Top of rail above ground must be 45” – legs must allow for a ½” variance in either direction by using adjustable feet.
  • Scenery at module ends must be roughly flat with no features (such as roads, rivers or track other than the modular tracks) crossing modular joints.
  • Roadbed thickness at module ends is 1/8th inch thick.

Module Height Diagram:

Module Height diagram

Module Height diagram

  • Scenery at module ends should include a strip of greenery across the board to disguise the module joint and help modules blend.
  • Modules with more than one modular end should feature at least one designated ‘main’ track that connects the modular ends together.
  • Main tracks, or any other tracks designed to be used by through trains must have a minimum of 36” radius curves and minimum #6 turnouts.
  • Spurs and industry tracks must be 24” minimum radius and can use sharper turnouts. Spurs or industry track switches can be located closer than 3 inches from the board end provided the any main or through track is straight.
  • Main line tracks must be code 83 (we use Peco as it’s now easy to obtain in the UK) – spurs and sidings that do not cross module ends can use smaller rail.

Module Wiring Diagram:

Basic DCC module wiring diagram

Basic DCC module wiring diagram

The only requirement for wiring is for the DCC track bus, which consists of one wire for each pole crossing the board joint.

The track bus connections are by 4mm banana plugs/sockets.

Some notes on the diagram:

  • Colour coding is shown only for clarity – boards can be connected either way round so the two rails cannot actually be reliably colour-coded across all modules.
  • We recommend (shown dotted on the diagrams) a bus wire to be run from one end connector to the other end(s) of your module – this will help with power transfer and ensure that one dodgy rail joint does not switch off every module ‘downstream’ of it!
  • You may add a connection into the DCC track bus to connect your own DCC system when it’s not being used on a modular layout.

 Other electrical issues

Pointwork needs to be controlled locally by your chosen method. Either through switch-machines controlled by a mini-panel (you will need to arrange your own power supply for this) or manually via push-rods or switch levers. If your points are manual please arrange electrical switching to make the frogs live.

 There is no requirement to build in a DCC control bus (such as Lenz X-Bus) – the reasoning behind this is that these modules could potentially be used on a layout running on any NMRA-DCC system. There is nothing stopping you adding a control bus and controller plug in panels for your own system – they will just be bypassed if the module is being used in a setup controlled by a different system.

For example – the RS Tower group use Lenz DCC, so some of the boards built by our own team will contain an X-Bus plug in – however we will also be using portable drop boards with X-Bus connectors to allow us to extend the X-Bus network to where it’s needed, even to boards with no control bus connection.

 Module Recommendations

  • Minimum curve and point specs are minimums. Your trains will look better on larger curves, and if you are building a module with a curved main line then adding transition curves will be very beneficial to smooth operations.
  • Be creative in your designs, why not follow a prototype’s curvature or add a junction or interchange?

Module Notes: 

  • There is no requirement for modules to be a specific width other than at the modular end.
  • There is no restriction on making curved modules apart from the minimum radius requirements and the need for a 3” straight at module ends.
  • There is no requirement for modules to be any specific length.
  • A module can contain any number of baseboards, and the internal baseboard joints in a module do not have to conform to modular specs.
  • Backscenes are optional – they can look nice on single-sided scenes but the centred track allows for modules to be connected in either direction, allowing for a curved module to become a left-hand or right-hand curve on the layout.
  • We currently use Woodland Scenics fine turf burnt grass as our basic ground cover colour for the board end scenery strips.
  • We currently use Woodland Scenics fine light grey ballast on modules as well.


11 Responses

  1. Re. modules, in the mid eighties I ,and a few other like minded modelers ,formed Southtrak ,a modular US based club here in Eastbourne . we used very simple specs as you are ,it worked very well for about 10 yrs until the specs slowly grew more complicated ,trying to please everyone …. stick to simple it works …
    re end of boards ….suggest depth between 4″-6″ …otherwise could end up with a 1″ depth trying to clamp to 8″…..also are you making length 4′ 6′ 8′ ….useful if you end up with a round and round situation …

    name ….. Freetrack ??????

    Good luck ….

    Regards Trevor …

    • Thanks for the thoughts Trevor, some good stuff there – interestingly from within the group all our initial module sets are specific lengths and specific curves to allow us to do things like a roundy or to build return loops (an end-to-end setup seems quite feasible with some of what we’re building using RS Tower at the other end for instance), but I would expect once we know we have enough modules to do layouts in those formats we might see some more varied idea’s in shape and concept maybe – who knows. 🙂

      Totally agree with trying to keep the “rules” to the absolute minimum needed to make the layout work.

      Thanks for the contribution.

  2. As I’ve said elsewhere, I really like the module standard. I agree with Trevor’s comment about depth of ends, but other than that I would say keep going as you are – anything more than 2″ spacing on straights will look odd. maybe allow easments on curves, but these will be within module lengths

  3. Some further thoughts.

    How about ModuleRS for a name 🙂

    The depth of end issue is probably important, since if my ends are 12″ deep and yours are 4″, clamping them together could be a pain!

    I was thinking of 6″ – enough depth for a two inch foam top and then a tortoise or blue switch controller?

  4. Oh, and do we need an end profile. i.e. is the track raised above the flat end profile on trackbed, or should it cross the end dead flat. My guess is on trackbed, but if so, do you need to specify depth of trackbed?

  5. Thanks for all the feedback guys, really good stuff. I think we’re talking about this kind of thing on Saturday so hopefully we’ll come away with all the questions sorted out and update the specs then.

    • Good timing – have a day off on Monday and plan to start my first module then.

      Maybe you can clear something up for me. I’ve no idea what a “4mm banana plug” is – is there a Maplins part number or similar I should be looking for?

      • Hi
        yes you can get them from Maplins.
        Plugs:- L20BH & L23BH ( red & black)
        Sockets:- N32AP & N35AP (red & black),
        other colours are available.
        Neil Rogers

  6. Cheers – will try to get to Maplins tomorrow then!

  7. Some unscientific experiments this morning on the “reverse curve conundrum”.

    If we assume 3″ straight at each module end, rather than the recommended 6″, we still have 6″ min’ between curves.

    I’ve tried my longest stock – SD40-2, autorack, 60′ hi cube, Gunderson maxi iv stack etc. thru a series of reverse curves of Peco 3rd radius (i.e. much tighter than the minimum mainline radius) both pulling and propelling, at considerable speed.

    With a 6″ (Ok, Hornby short straight which is about 61/4″ actually) straight between each reverse curve nothing fell off. Not even when whizzed thru by hand, so all the buffing forces were at odd angles.

    I’m therefore planning to go with just a 3″ minimum straight at the end of my modules. Not that I’m planning to deliberately include reverse curves of this severity, but the experiment convinces me that it should be OK in everyday use. I appreciate a train of Superliners, Autoracks or 86′ box cars will look odd swishing thru such tight curves, but the format I’m planning for home use doesn’t include any S curves, its just useful to believe they should work if ever connected in that format.

    • Okay guys – module specs updated.

      Quick list of the main changes:

      *End straights drop to 3″ – on the real thing you would have a transition curve between any S’s on a running line (not including crossovers) to ease the curve down to nothing and then turn it the other way, that’s impossible to specify in this kind of thing so I think that there needs to be some straight spec in here to effectively transition it – 3″ I think will still do that job whilst allowing a few extra precious inches on the module so 3″ it is.
      *Track spacing remains 2″ centres but we’ve referred the reader to the NMRA track spacing specs if they are building double track curves, they may need to spread the tracks accordingly to retain clearances.
      *Board end height needs to be between 3.5″ and 4.5″, ours are 4″ and a standard 75mm clamp can accomodate around an inch of difference, 4″ can accomodate tortoise motors assuming wooden construction.
      *1/8th inch roadbed (we use cork) height above flat board ends, this is included in the 45″ total rail height.
      *We’ve added our “standard” greenery and ballast specs for the ends as well, not compulsory obviously but I think we will be using it for all our groups modules.

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