Thursday, December 10, 2009

Designing my train layout - 3 - Folded dog bone

Building on my experience with my previous layout, I decided to start by investigating single track main line designs. Basically, what I wanted was not much more than this schematic:

In other words, an oval with two stations. I wanted a reasonable amount of separation between the two stations. I wanted the train to have at least a short run between the stations. This schematic may seem very simple but it should be noted that complex behavior can arise from deceptively simple systems. Consider for example the difference between a simple and double pendulum. While a simple pendulum can be fully described by equations for simple harmonic motion, the tip of a double pendulum can move chaotically. In an analogous manner, even with just two stations, it is possible to create complex patterns of train movements. Having decided on a two station configuration, the next step was to see how long a main line I could fit within the space available available.

I prefer to do my design work directly on the computer using the 3rd PlanIt layout CAD software from I have been using this package for many years, initially using to design sectional Märklin layouts. I think that 3rd PlanIt is a very powerful package and there is indeed quite a bit of a learning curve. However, once you get the hang of it, 3rd PlanIt just seems to get out of the way and lets you explore designs very quickly.

The first general shape I investigated was a folded dog-bone. I have seen this shape used in many track plans and tried to get it to fit in the space available.

The nice thing about this shape is that there are good locations for locating the stations allowing decent separation between them. However, the main problem is that the curves at the end of the "bulbs" necessarily have to be very tight. Nothing more than 20 inch radius curves can fit in the space available. another problem is that access to the interior of the layout would be problematic.

In order to use curves of minimum 24 inches radius, I discovered that there were two options, neither of which were attractive.

1. Overlap the bulbs: This allows two large radius bulbs to be accommodated. However, as previously mentioned, I was not keen on a multi-layer layout. A second problem is that by having the bulbs on different levels, the main line and the stations must necessarily be on an incline.

2. Widen the layout: Widening the layout allowed the use of 24 inch radius curves but the increased width unacceptably cut into walkway around the layout. One more problem that I discovered was that the station passing loops could not be made very long. I don't really want very long trains but this seemed a bit ridiculous - barely 41 inches for the station on the top.

Clearly a folded dogbone was not going to work for me. In my next posting, I will describe some exotic variants of the folded dogbone that I tried.


  1. Glad you liked it. There is much more to come. After I get through the design process, I'll describe how I built the layout and the control software.