The wheels are the only components on the robot which require any considerable custom fabrication. Surprisingly, we couldn't find a commercially available rubber wheel a few millemetres across! We had a look around for suitable rubber washers, etc, but found nothing. Instead, I developed a simple method of mass producing the wheels from neoprene sheet.

I machined these simple tools on the lathe. The tool on the right is the wheel cutter. On the right is a 5mm steel rod drilled through 3.5mm. The end is machined down to form a thin-walled tube. This tool is loaded into a pillar drill and used to cut 3.5mm wheels from sheet. Alternatively it can be used as a stamp with a hammer, but the resultant wheels are not as clean as those cut with a rotary action. Many wheels may be cut sequentially, stacking up in the tube and chuck, before it must be removed from the chuck and emptied out.

A needle is used to cut a concentric hole in each wheel to accept the axle. To aid this process, I made the jig on the left. It has a 3.5mm recess to hold the wheel and a concentric 1mm hole to guide the needle.

With these tools mass production of wheels is feasible. Around 100 wheels were made in 20 minutes or so. The wheels are a simple friction fit on the axle.

It would be worth experimenting with different materials here; the neoprene has excellent grip but wears quite quickly - after driving for a few hours the wheels become visibly conical. A harder rubber may be better.

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