T-TRAK-Z - Tabletop Modular Z scale Railroading - Standards revision, guide, and recommendations

Created by Josh Murrah and Vic McTee, Revision 1.4, 7/11/2018

What's being changed, and why?

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 The track system choice is out of date, and the lengths and geometries were never considered beyond a basic rectangular shape.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


Track system - Rokuhan

The current T-TRAK-Z specs call for the Micro-Trains Line track system. At the time the specs were written (a decade ago), this was the only track system available that had a sturdy plastic/metal joiner that would be durable enough to secure modules like Unitrack does for N. Fast forward to 2018, and the initial track that MTL put out, is still all that's been released. There's a few lengths of straights, two radii in only 45 degree arcs, and no real way to assemble anything other than a basic rectangular module assembly. In contrast, Rokuhan has a robust mix of the MTL 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. Therefore, the first proposed specification change is from Micro Trains to Rokuhan track.


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

This is the same as the previous specification. 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. As previously stated, there is no change for this specification.


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. 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

This proposed change includes the original specified common corner radii but recognizes wider radii as equally important.

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. This is the next proposed change to the current specification (from 330mm down to 220mm) along with a corresponding decrease in the module size from 328mm down to 218mm.

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. This proposed change for module depth, from 286mm to 270mm, is a minor adjustment to allow for better cable access behind the modules.

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). This is the final change to the existing specification as this was not previously specified.


In summary, the proposed changes to the existing T-TRAK-Z specifications are as follows:

Current Specification Proposed Specification Benefit
1 Micro Trains Line Micro-Track Rokuhan Z Gauge Track Larger variety of track pieces, especially curve radii
2 Single Module Track Length - 330 mm Single Module Track Length - 220 mm A much better fit for layout geometry
3 Blue Line Track Offset 3" Blue Line Track Offset 3" from center of track clarify track offset measurement method
4 Single Module Length - 328 mm Single Module Length - 218 mm Corresponding module length for new track length
5 Maximum Module Depth - 286 mm Maximum Module Depth - 270 mm A slight decrease to accommodate cabling and to round off dimensions
6 Common Corner Module Track Radii - r195/220 Common Corner Module Track Radii - r195/220, r220/245, and r245/270 The family of curves provide plenty of options
7 Corner Module Dimensions - 2952 mm Corner Module Dimensions - 2952, 3202, and 3452 mm Corresponding module sizes for family of curves
8 Electrical Connectors - TBD Electrical Connectors - Rokuhan with opposing polarity A specification for a previously undefined item
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