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Track Laying
I planned to use Peco code 55 track from the outset. This looks nice, has electrofrog points and has the "scissors crossover" available.
I wanted to avoid curves that looked daft, while space constraints did not permit prototypical radii. Most rolling stock is specified to operate down to 9" radius; I tested several trains and they negotiated it with ease. (I do know that some co-co type diesel locos will NOT run reliably around 8.5" radius bends).
The Peco 26.5mm track spacing leads to collisions on tight corners, and that spacing can only be used on 15" and above radius. Realistically, to allow margin for error, the minimum radius used for that spacing should probably be 18". At smaller radii, the gap needs to be opened out by 3-4mm.
In practice I have tried to avoid 12" radii except in hidden areas, and most curves are nearer 18" radius. All visible pointwork will be medium radius (18").
Gradients
The layout has multiple levels. I wanted reasonable sized trains to be able to run without difficulty, so I needed to know that the slopes would be manageable.
To find out what slopes could be used, I conducted some tests using three locos with realistic loads:
-
Kato "Eurostar", pulling its 8 carriage rake;
- Farish class 47, pulling 4 carriages + the weight of 4 more;
- Farish 0-6-0 PT, pulling 4 carriages + the weight of 4 more
The conclusions were that in a straight line, these trains would start from standstill on a 1:35 slope and 1:40 was comfortable. I wasn't able to try the effects of a full axle count, or try pulling trains around corners. Consequently I've concluded that I still need to allow some margin.
In practice, my worst case slopes are around 1:60. They were planned to be better than that, but I've kept changes in gradient away from points etc and that resulted in shortening of some of the slopes themselves.
Train Lengths & Blocks
A piece of timber marked with the lengths of various trains has been very useful for final checking of the design. It is planned to run trains with a locomotive and 8 carriages. Some typical train lengths are:
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Class 47 loco + 8 65' carriages: 1275mm
- Class 47 loco + 8 bogie oil tankers: 1133mm
- 8 carriage Eurostar: 1060mm
The design needs to take account of train size for automatic control: the sections between signals need to be slightly larger than the maximum train length and "blocks" for automatic operation will probably follow the signal positions. Each block needs to train detectors: one to sense occupancy, and another to sense the train being at the end of the block so that it can be told to stop. Some detective work led tothe following measurements:
-
The minimum distance between the start or end of a block and a point (measured from the rail join to the peco point itself) is 55mm. This is to make sure that a train stops or starts clear of the point, allowing a train on the other track to pass.
- The "normal" part of the block shall be at least
1280mm, to accommodate a maximum length train.
- The "stop zone" part of the block shall be an
additional 140mm (this is the zone fed be the second block detector).
- The stopping distance will depend on train speed. The "planned" stopping point is approximately 50mm inside that zone.
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