SYNCHRONISED TRAINS

In a perfect system, a precise world, the synchronised repeated journey of each train would never interfere with that of the other, but in practise the trains come closer and closer to occupying the same space at the same time and within a few minutes they hit one another.

KEY TO SYMBOLS

To clarify each synchronisation, I have used a system of symbols similar to electrical circuit diagram symbolism.

	(in all other diagrams, gravity faces into the paper)
Gravity Loop: This is the first loop I made, before I bought trains in which the motor can be switched to run either direction. This meant I had to use gravity to make the train return to the start of the track: it climbs the hill, the motor is switched off, it falls down the hill, and with its momentum it switches its motor back on again. This loop appears elsewhere in my documentation.
‘O’ Loop: The trains swap ends of the track endlessly. This loop functions because the points act like transistors. They can be in one of two stable states, their two directions. The direction the points guide the trains in can be changed by the trains themselves – if the train approaches the points from the opposite fork to the one they are pointing to, it will flip the points. Crucially, like a transistor, the points then keep this state, in effect ‘remembering’ which direction the trains came from, and sending them back in that direction when it passes over them again.
‘Y’ Loop: The trains share the tip of the ‘Y’, so when one train is there the other should be at the tip of one of the forks. This also relies on the similarities between points and transistors; when each train leaves the tip of the ‘Y’ it is sent back into its own fork, the one from which it came.
	(here the points are connected so as to mirror one another)
‘U’ Loops: Here the trains share the track between the two opposite ‘Y’ shapes, but each describes a ‘U’ shaped path. The points are connected so that when a train enters the straight between the ‘Y’s and flips the points it crosses over, it also flips the points at the other end of that straight.
	(here the points are connected so as to oppose one another)
‘S’ Loops: The track layout here is identical to the ‘U’ Loops, so instead of an overview the picture shows a closeup of the point connection mechanism: you can faintly see the thread running alongside the track, and the points must be raised to allow space for the mechanism. The trains follow opposite ‘S’ paths around the track because the points always oppose one another.
	The track layout in the photograph is curved only to minimise the space it occupies.
Two direction reversers on same stretch of track: Here, one train has a paperclip on its side that allows it to switch a lever on a direction reverser to turn it on or off. When it travels over the reverser plate, it turns the plate on, causing the train’s direction to reverse, and the paperclip turns the plate off again. Therefore only this train is affected by this plate – the other passes over it.
	The set of points and direction reversers at each tip of this square are connected so that when a train reverses direction, the points flip to send it out the opposite way to that which it came in.
4 Train Progress: Any train placed on this track will visit each point of the square in turn. Therefore 4 trains can share this track as long as they set off equidistant to one another.