Depends what you hoe you want to put it together.

Cylons gear box has a spur gear on the motor (8mm shaft with a grub screw through the gear and shaft to hold it in place)

The other gear is screwed directly onto a wheel and runs on a 12mm stainless steel axle. This sits inside a plastic 12mm mount.

What I found was that it is good to drill the holes by sticking the gears in a lathe and you will need some tough drill bits as normal HSS will burn out.

Having driven it a bit it keeps veering off to the right but we (Well Froggy actually) came to the conclusion that this is probably to do with the fact that it needs a couple of washers either side of the gears to hold them in place.

We used the 150w gold motors, but should be the same for any of them.

I also found it ran better and took up less space if you cut the boss off the back and smoothed it over with the lathe. It also means youre not fouling the motor in anyway with the boss.

Andy