The photo above shows the chassis without the body fitted. Note that the motor shaft has bearing on the far end. This removes the tendency for the worm gear to climb up out of mesh. It's just a simple brass bush soldered to a small brass bracket. No great strength is needed as the 1.5mm diameter shaft is quite rigid in itself. In the photo below, you can see the relationship of the chassis to the body. The motor sits rearward in the cab and bunker area, while the side tanks are full of lead, leaving just enough room for the worm and motor shaft. The frames are phosphor-bronze sheet, 0.25mm thick, soldered to printed circuit board chassis spacers. The copper surface of the spacers is gapped to insulate one frame from another (you can just see the gaps below) using a razor saw, cutting just deep enough to break the copper. The motor is electrically isolated from both frames and the body has a layer of Sellotape to prevent it shorting out the frames. A very simple chassis, but so far, very reliable.
