Originally i was going to use a castor wheel. When i saw the tracks i thought they might be good, though after some research and some advice, i decided these would be too slow. I whent back to the idea of a castor wheel. The ultrasonic sensors also seemed attractive at first, with the ability to measure distances. After looking at the price and weighing up how much I wanted to spend, they were just too expensive. So castor wheel and infrared it was. I connected the standard battery pack to the picaxe, three AA batteries, 4.5V. This, however, was not enough to do a significant amount of testing with LED's before the voltage became too low. So I went with two voltage supplies. One 9V supply, regulated to 5V for the picaxe, and one 6V supply to the motors. For my castor wheel, I went with an aluminium bracket for strength and light weight. I used acetal for the wheel with a rubber oring in the middle and tapered on either side with two sealed bearings for smooth operation. The castor rotates via another sealed bearing wich allows smooth, faultless manuverability. The narrow wheels were definately the choice wheel, again with manuverability in mind, the small footprint allowed accurate turning in tight spots. I tested the tamiya gearbox on a ratio of 38.2:1 and this was too slow, i tested 344.2:1, and at the time this seemed too fast and uncontrollable, so i settled with 114.7:1. TAFE supplied the perspex for the base and my design retains a usable amount of space while rounded corners reduce the chance of being caught on corners. And this is how i arrived at my final design.