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Design Log

I have spent a considerable time and effort on making design sketches which follow my objectives and preferences. So, for the next few days I shall write some summary notes before proceeding further. A preliminary note is that I am increasingly driven to the conclusion that I must build a portable railway or have no railway. But no railway means no progress on projects. Hmmmm. [dajo 2 Sep 2013]
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These are things that are important requirements. A railway that does not meet these objectives, probably I shall consider not worth building.
  • Manageable by One Person. This means that the railway must be an assembly of pieces that are not too heavy, not cumbersome, etc.
  • Permit Multiple Railway Designs. Railways of different sizes and shapes must be accomodated. This means following some of the ideas implemented in toy train sets, such as standard straight and curved sections that can be assembled in arbitrary order. Also, it means that it must be fairly straightforward, relatively fast, and relatively easy, to make a couple of new modules to accomodate a new railway configuration. A corollary of this objective is that expansion of a small railway must be simple.
  • Support Experimental Projects. This means support for both gauge 1 and gauge 3 at a minimum; also it means a large minimum curve radius, to support long-wheelbase rolling stock.
  • Glitch Free. The assembled railway must be smooth running. Derailments must be very infrequent and due to operator error. Any junctions must operate well and be flagged to show point position.

    This objective comes about because I have seen too many glitches on other railways; and they can be expensive for someone. I have a clear memory of running in Sacramento early on the last day of a meet, when most people had gone home. The tracks all were clear and I thought I could run a long train very peacefully; I started out really looking forward to it. What happened was a nasty tip-over. It seemed that the plastic sleepers of the first junction reached by the train had been attacked by burning alcohol, probably on the evening before. A number of my expensive train carriages ended on their sides, fortunately not on the concrete floor.

    The track on the NG&DR was quite good in its freedom from glitches. I remember only two track failures, both more serious than I ever want again, one a loose check rail, the other is beyond my memory; but they both resulted in engines falling off the track and down embankments. In general, derailments occurred mainly because of operator error, occasionally because of fallen tree twigs, or ballast stones blocking check rails or jamming junction points. So I feel this objective can be realized with some thought.

  • Robust. Damage is the issue addressed here. And damage usually occurs during packing and unpacking, to and from storage, rather than during use. The railway must be easy to store and be self-protecting with built-in stand-offs, or something functionally similar.
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These are things that I want; but, to some degree, they are mechanisms to implement the above objectives, and involve conceptual design decisions that can change.
  • Small First. This is rather obvious: the first railway should be as small as possible without compromising any later desire to expand.
  • Quiet I want the railway not to make noise by vibration of the baseboard, usually manifesting itself as a hollow "empty box" kind of noise. The railway modules should not be drums. This is not about rail hiss, nor clickity-click, nor noises generated by the locomotives.
Hardware Design
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I have reached a stopping point on this project; to some degree driven by outside factors, but also because I have created a design which I plan to use as a proof-of-principle and testbed. Considerable work remains on detail drawings, but I have made decisions that have resulted in a General Arrangement, and all the key concepts have been decided.

This first design is referred to as Track A. The key features are as follows.

  • Track A comprises six straight modules, supported on seven legs. Two different modules widths are used; and two different track gauges are planned, although the latter is independent from other design issues. The railway is nominally 24 feet long, is dual gauge and is not continuous; a re-configuration creates a nominal 36 feet, single gauge, railway. The chosen height, floor to railhead, is 3-1/2 feet.
  • The load-bearing structure is aluminium. This is screwed together, rather than soldered or welded; the latter may be better in the future.
  • The inter-module connections are aluminium, and are designed to allow flexibility in connections. The module ends are positioned with a plug and socket system, and are held together with over-centre latches.
  • The load-bearing structure is supported by detachable legs that are steel weldments mainly made from 3/4 inch square steel tube. A detachable leg arrangement spreads the weight for transport, allows for re-design of one component without affecting the other, and, I hope, will simplify storage. Detachable legs also allow extra-long legs or whatever is required to handle uneven running locations.
  • The basic load-bearing structure is a ladder made from 1-1/2 x 1/8 aluminium bar sides and 1-1/2 x 1/4 aluminium bar stretchers. The legs support the ladder by having a slot into which the stretchers fit. The legs are braced, but brace design is to be decided later, probably after track A is built.
  • All module centrelines are 71 inches long; this size has been chosen to allow for rail manufacture from the standard six feet length of suppliers. This is particularly important for curved modules.
  • The railway baseboard design is under consideration. The current design allows 1-1/2 inches from aluminium to railhead; it is expected that this will allow a solid support baseboard, sound deadening material, sleepers, and rail.
  • No costing has been done. A guess is $100-200 total per module; thus a 24 module railway is estimated to be in the range $2500-5000. This is the cost of a single medium to medium-high price gauge 1 locomotive.
  • A considerable amount of work has been done to ensure that the concepts in the straight modules described here transfer to curved modules, including variable radius curves such as transition curves. Similarly, junctions, sidings, steam-up bays, etc. have been investigated. It has been decided that the straight modules of Track A will demand development enough, and that curved, and other complex, modules are best left until later.

Conceptual Design
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Another facet of design has been production of computer code that generates a railway layout. Modules are represented as a set of vectors, and are not otherwise constrained. Existing hardware modules can be measured and handled by the code; this permits non-standard modules to be codified and incorporated into a railway design. Also included in this code is implementation of the shapes described in Transition Curves.

The layout on the left is an approximation of the current target railway intended to satisfy the Objectives and Preferences above. The straight railway modules are re-used from Track A, although they are not shown accurately here. Also, what is shown is single, not double, track. This layout has nominally 15 feet radius curves, together with transition and easement modules next to the straight modules.

Just for grins, a railway design that came out of the code development is shown on the left. This shows both the flexibility of the computer code, and what it is hoped can be achieved by the actual module hardware. Note the curve reversal, achieved by turning around modules to make them concave, instead of convex, curves. This is a demonstration of use of the toy train standardized module shapes also mentioned in the Objectives above.

This is a large railway, using a lot of modules. All the curves have transition entries and easement exits from and to the straights. There are six special length straights in the railway which are necessary to fit the standard modules together; they are coloured yellow. And, yes, I did this for the fun of it. The layout is about 100 x 80 feet, but the final join closes to within 0.08 inches, even with the integration approximation used for the clothoid curves.

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last-modification-date:  4 Jan 2016