Introduction
A few years ago, shortly after I first heard about the idea of von Neumann machines (entities that can make copies of themselves, including living organisms - von Neumann was the first to prove mathematically that such a thing was possible by purely deterministic means without invoking some special property possessed only by living things), I wondered if it would be possible to make such a thing out of Lego. I have since given up on the idea having realised that, if not impossible, it would be a) extremely large and b) extremely complicated. I have, however, managed to make a series of models that could all construct objects of varying complexity out of Lego bricks. A technical explanation of the various revisions is given on the pages listed below. I am aware that the description is very involved, and might not be easily comprehensible - if you would like to make any suggestions that would enhance its readbility, please contact me.
I had thought I was the first, if not the only, person to come up wwith this idea but I was incorrect. There is one at an American university which is hugely more complicated than mine and actually builds proper cars, though I protest that they give it partially-assembled models as "raw materials" whereas mine work from isolated parts; they use it to teach manufacturing engineering students about how to control an assembly line. I also saw a model on the Lego Mindstorms website which could build a wall of arbitrary size and height out of standard 2x4 bricks - the model moved on wheels along the wall as it built it, and dropped a stack of batteries on each new brick after it was put in place to stick it to its fellows! I no longer have a precise address for it, however, if indeed it is still anywhere on the Internet.
Versions of the assembly line