Back in late August, the first bit of progress happened – tyres! With a daily commute that takes Rob past Red Lodge Karting in Cambridgeshire, Go Kart tyres were the obvious choice for Big Dave 3 – large enough to provide traction on a slippery Glaswegian hangar floor, abundant enough that other roboteers would use them and have experience hooking them up and with cheap enough parts, Rob called up Red Lodge Karting and after an extraordinarily bemused owner was told about the project, he happily donated as many tyres as would fit into Rob’s car! As we weren’t sure in the direction we were going, we got equal numbers of front and rear tyres, and with Rob’s impression of the Michelin Man done, the first step of the parts acquisition was complete.
Back in AutoDesk Inventor, and with Rob’s obsession with a tiny ground clearance, we decided to go with the front tyre size – confusingly, the only bits of the build that are in imperial measurements at 10” x 4.5” – in real money, 254mm x 114.3mm. With our frame plates (and yet-to-be-revealed special ingredient), that leaves us with a ground clearance of 5mm on either side.
Fast forward through the design, we ended up going with HTD5-15 belts for drive, again due to their abundance and relative ease of use. After some trawling through the FRA and associated forums, we decided to gear our motors down. Our chosen reduction ratio is 1:5.33, which should give us just over 12MPH as a top speed at 22.2V.
Come the first build weekend, the tyres and rims from Jet Karting didn’t want to play ball – it took all three of us several attempts before admitting defeat and turning to YouTube for advice. Ali and Chris figured out that if you put some lube on the inside of the tyre and kept pressure on it as you fed compressed air in, one side would eventually seal, and then it was just a case of manipulating the other side into fitting. Took far longer than any of us would like to admit, but it worked!