Here are some details
I exchanged the original drive shaft with a 2 mm steel shaft. You can easily remove the bevel gears from the original shaft. The new shaft fits perfect in a brass pipe with 2 mm inner and 3 mm outer diameter. The pipe is glued into the lower chassis part.
The two chassis parts are joined together by a ball bearing with 6 mm outer and 3 mm inner diameter. I pressed the ball bearing into a 3 mm thick sheet of alloy, which i screwed to the rear axle. That's it.
in parts
bottom view
The pcb i used is from a kyosho mini-z.
diets - selfmade decals, what a horror trip