Production

This is a log. In other words, this writing is proceeding more or less as the work progresses. As a result, the final effects of design features are not reflected in the writing; speculation herein may turn out to be wrong; and the design may change as production proceeds 8-).

Legs The minimum number of legs required to support the target railway is arguable. It was decided that 42 would be adopted; this is 2 for each of 20 modules, and 2 extra to set-up the first module. However, also it was decided to make spares while in production mode, and so a target of 60 was established. 6 legs already exist from the prototype work, leaving 54 to be made. It turned out that two kinds of leg were made, explained below; but the total made is 60.

The problem, experienced when connecting the prototype modules into a railway, was that the legs would fall out of the module sockets whenever the module was moved. Moving a module is an infrequent occurance, happening only during railway set-up or tear-down. However, having a leg suddenly go away was irritating; and various solutions were dreamt up. After a while it was realised that 20 modules have 120 sockets for 40 legs, so applying a solution to the legs rather than the sockets made most sense. The current solution is to glue a magnet into the upper end of the leg. This magnet "sticks" to the washer already in place in a module socket and holds the leg in place during module movement.

One development problem was that the chosen magnet, advertised attraction force 4.95lbf, would not support a leg, weighing less than 1.25lbf, under installation and test conditions. The magnets are faced with a 0.046in steel washer, which attenuates the magnetic flux; and the test conditions include shaking the module until the leg rattles in its socket. Gravity won in testing. The solution to this problem is to use four magnets per leg on 24 legs, and do more field tests to establish effectiveness of the system - the problem is an irritation, not a fatal flaw; the solution must not be worse than the problem. A single, larger, magnet can be retro-fitted to the non-fitted legs if desirable; the downside is a $4 increase in the cost of each leg.

A second development problem arose with epoxy glue. When the leg under test fell, onto a concrete floor, the glued joint shattered, and the magnet fell out. This happened twice out of two tests. Current thinking is that, when the aluminium tubing hits the floor, it rings and flexes the joint enough to break an epoxy joint. The solution to this problem is to change to a flexible glue; GOOP is the present selection, which appears to be strong and flexible enough.

The sleeves for the clamps were turned to reduce size prior to glueing, as indicated in Manufacturing; and three dozen of the finished legs look as shown in the images there. The other two dozen legs have magnets fitted, as shown here; and the legs without a magnet are identified with red tape on their feet. My hunch is that the magnets will prove to be desirable, and the tape can be removed as magnets are fitted.

A box of legs.