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computational train track layouts


Duplo Layouts

Duplo is a train set system made by Lego®. It is well built and a great toy for kids. There is a useful Eurobricks forum on Duplo trains and track.

It is ideal for testing computational layouts as it has the two different types of point required: 'lazy' and 'sprung' (as pointed out by Robert Cailliau).

The current 'new' point is a lazy point. The older type has an additional spring mechanism beneath the track so it behaves as a sprung point.

Duplo Points

Duplo points have a red lever that is set by an operator to guide the train onto either track.

New 'Lazy' Points

These are switched by a train arriving on the 'wrong' branch line. The train wheels simply push against the lever, forcing it to switch over.

Duplo lazy point
A new lazy Duplo point

Old 'Sprung' Points

The 'old' type of point allows the operator to set the lever to guide the train onto either branch, but, the train cannot switch the point when arriving from a branch line.

The 'old' points remember the branch line set by the operator. The 'new' points remember the last branch line the train arrived on.

Duplo sprung point
An old sprung Duplo point

As both types of points are available for one system, it makes sense to build some of the train track layouts using Duplo track. However, with only a 30o turn instead of (possibly unrealistic) 90o turn, layouts are a good deal larger.

Here are a few Duplo layouts:

Count Up (increment)

Count Up function
count up
Click layout to pause/run train Click points to switch 0/1 Click start circle to reset train/points

Each stage is built like this:

Duplo counter stage

The complete counter layout. The right hand loop just serves to return the train.

Duplo counter

Peter Nolan from the Duplo Trains Forums has made this layout and posted a video on You Tube !!

A 2-stage counter can be bent round and the end loops overlapped to create a more compact rectangular layout. No one needs know its computational origin.

Duplo APV rectangular layout

Equivalent Circuits

The old types of Duplo point are available on eBay. However, they can be emulated with two linked lazy points. Also see equivalent circuits.

Duplo sprung point sprung point

And a cross-over point equivalent layout.

Linked Lazy Point Cross-over
cross-over (lazy)
Click layout to pause/run train Click start circle to reset train

Duplo cross-over

Flip-Flop Circuit

An important circuit is a flip-flop. This needs both an 'old' style sprung point and a linked pair of lazy points (a co-operative point).

Trains arriving on the main line are diverted up into an inverter loop and then exit the lower lazy point on alternate branch lines. Also see equivalent circuits.

Adam Chalcraft and Michael Greene in their paper 'Train Sets' name the circuit a 'Distributor'. Without the use of linked points they must construct a layout of infinite size.

flip-flop point

Duplo distributor

And here is how it looks as a Duplo layout.

Duplo distributor layout

Auto Switching Layout

This uses 2 pairs of linked lazy points. See Auto Switching Layouts page for more layouts.

Duplo track plan

Duplo track layout



zoom in to enlarge layouts