Back in year 7 or 8, i was browsing through a book on robotics in the school library. In it i came across Gray Walter's robotic turtles Elmer and Elise. These were two robots built in 1948 which were very simple but completely autonomous and very life like in their behaviour based around the intensity and direction of light. The book had a picture of it with it's cover off. I thought 'That doesn't look too hard'. Unfortunately, I never got around to building it until last year at the same time I was building TIM, but it turned out not to be nearly as easy as I first thought.
I made the front wheels, steering and chassis out of bit's of old change machines (my dad builds them so there were lots of spare parts). Then it came to the circuitry. I did many hours of research into how they worked and behaved, and i eventually came across the original circuit diagram. It consisted of two tetrode valves and two relays, with a couple of other passive components thrown in. Not having any valves, i redesigned the circuit using transistors. This required a full understanding of how the circuits worked. Now not being particularly familiar with valves or transistors this wasn't easy, but my dad helped a lot and we eventually got a circuit that worked. put it all together and a lot of tweaking and it finally worked.