It's very helpful, thank you! And maybe it would be slower, but wouldn't the 24:1 ratio give it better pushing power? It'd only be a temporary fix anyway, just until I could make some from scratch... I will have a good look into it though, if I can find a solution for the gears too I'll post it here! As for wheels as well, I'm not sure what size I'm going for yet, need to finalise my design yet - just working out what parts to buy at the minute and then building a prototype with some offcuts of MDF I've got laying about!