T-TRAK-Z - Tabletop Modular Z scale Railroading - Standards and recommendations

Created by Josh Murrah and Vic McTee, Revision 1.5 by Josh Murrah, 8/6/2018

Interactive group area: https://www.facebook.com/groups/ttrakz

What recently changed, and why?

T-TRAK-Z, as of mid-2018 had never taken off, and the feeling is that it's partially due to the previous specifications. The track system choice was out of date, and the lengths and geometries were never considered beyond a basic rectangular shape. This document details a system that is mostly driven by the new track system and its broader radius options, and geometry that allows for larger, more interesting layout designs.


Track system - Rokuhan

Rokuhan has a robust mix of the old spec'd MTL track geometery with very similar joiners, but has the larger radii, wider variety of track lengths and a capability of types of super elevation & concrete ties that exceeds what Unitrack provides. I have been able to recreate all of my T-TRAK-N designs in this smaller scale using this system. Rokohan track is imported to the US by Ztrack, who is also the distributor for AZL. Modeltrainstuff.com carries the full line as well as any local dealer who can order AZL.


Track set back - 3 inches / 76mm From Fascia Edge to Track Center Line

The three inches is perhaps overly generous, but we have the room for it in Z scale (all the below curves still allow a layout to fit on one table), and it will allow for two sidings on the front line plus a "train wreck" easement, or will instead allow some nice scene/scenery options. There's also lack of rearward scenery area on the module, so the front area helps.


Corner radii - three options - 195mm/220mm, 220mm/245mm, 245mm/270mm - minimum mainline radius 195mm

Rokuhan provides a wide number of radii, spaced 25mm / 1" apart. The two core/key radii are 195mm & 220mm. That is what is provided in the starter kit, and they are the two radii available in both 45 degree and 30 degree sections, along with being the radius pair the curved turnouts are designed for. Any radii smaller than 195mm on main lines are not allowed for mainline. Designs have been created for inside/outside corner geometry, T-Junctions, star junctions, various yards and working single and double line balloon loops, in all three radius combos all without cutting any track sections. When planning a layout, there needs to a single radius combo choice, as the three size options will generally not work together. Local clubs should determine their own optimal radius, and build corners and junctions to work with their choice.

  • 195/220 corner module: 295mm (approx. 11 5/8") depth/width
  • 220/245 corner module: 320mm (approx. 12 19/32") depth/width
  • 245/270 corner module: 345mm (approx. 13 9/16") depth/width

Module dimensions

Rokohan has a geometry of 220mm. That's the multiplier that makes all the various radii work, and is also the length of a double crossover, much as the width of T-TRAK-N modules and Unitrack crossovers are both 310mm. That means all modules need to be a multiple of 220mm.

The module max depth is one inch less than a 195/220 corner, which makes it 270mm (approx. 10 5/8"). This does allow for a small central trench for bus cables and backdrops. Regardless of what radius your club uses, the max depth has to conform to the smallest radius. To state this another way, if you build the modules deeper, the modules will not fit into a smallest-radius layout. To make interoperability easier this standard will not include support for modules deeper than this maximum, but they are allowed as long as properly planned. Some examples of planning for very deep modules include such things as a 2" bottom-facing pass through channel for tabletop bus cable, and running sets of modules back to back in a specific area of the layout for geometric or aesthetic reasons.

The module height is the same as T-TRAK-N, 70mm / 2.75" with a additional foot adjustment of 32mm / 1.25". There was some research into scaling down the module height and it would be more pleasing looking, however the hard fact is that the electrical accessories don't actually scale down, a good example is the Digitrax UP5 front panel mount which needs the full 2.75".


Dimension summary:

  • width: multiple of 220mm with 1mm setback on each side
    • single is 218mm (approx. 8 9/16")
    • double is 438mm (approx. 17 1/4")
    • triple is 658mm (approx. 25 15/16")
    • quad is 878mm (approx. 34 9/16")
  • max depth: 270mm (approx. 10 5/8")
  • height: 70mm / 2.75" with a additional foot adjustment of 32mm / 1.25".

Backdrops - optional but highly recommended - 178mm / 7" recommended height

There will be a central trench in almost all cases. Since there is a trench, there is an optional, but highly recommended practice of using backdrops to help hide it for beautification purposes and general use as a backdrop/view block. Due to the module not being as deep and the track being set quite a bit farther back (the backdrop height is limited by the need to see your train on the opposite side), the backdrop needs to be 7" total, with only 4.25" visible above the back of the module.


Electrical - Rokuhan connector/feeders for modules, opposing polarity on lines, buses & DCC recommended for larger layouts

The module plug is the Rokuhan power plug. The Rokuhan feeders need to be inserted from the outside facing edge of the lines to ensure opposing polarities (aka BWWB wiring). DC controllers are to be used for small layouts, mid-sized layouts can add in power splitters and extensions, and then buses and DCC on one or both lines for the largest layouts. For the largest setups, a powerpole-based sectional bus is highly recommended, this can be a single pair reversible cable, or inside+outside pairs, or inside/outside/12VDC to add accessory power (refer to the Tutorials Wiring Section for information on various cable systems).

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