Very clever design using the cam. It's also interesting how Robin has a different perspective on the 4RowBot.
I built the 4RowBot (took me a week to learn how to compile Lejos Java apps , in particular, packages - it's all about the paths!, I digress). I agree you have to make sure the board is aligned perfectly, and the background light has to be even so the colour sensor works ok, but I love the overly complicated mechanics like the chain drive
I assumed using a webcam instead of a colour sensor would simply be "better" but so far I've found they are are about equal (obviously Andy's project is about mastering a specific goal which he's done wonderfully).
The classic robot that uses the colour sensor to the max is Tilted Twister 2. Once built correctly, and operated in a gloomy lit room, it works flawlessly. And uneven or bright light and it fails a lot.
I thought the scanning process of TT2 was too slow and that using a webcam solver would speed things up, being able to scan a cube face all at once. In reality I've found it is on a par with the colour sensor as webcams are really succeptible to uneven or too bright light when being used to determine colours. While testing my current cube solver it's been driving me mad. I get the best results with natural daylight. At night time, overhead bright lights are a no no, and I frequently have to shade the machine with my arms and hands to get successful readings.
btw - here are videos of my builds of 4rowbot, and another mini one that uses NXC
Anyhow - on a tangent I guess, but well done Andy - very nice!