LEGO wheels are excellent for building robots and other mechanical contraptions. Modifications are often necessary for LEGO wheels to attach to non-LEGO axles and motors.
One choice is to create a coupler with a side that connects to the motor’s shaft and another side that connects to a standard LEGO cross axle (see a picture of such a coupler as used on the Sandwich robot). The LEGO cross axle connects to most standard LEGO parts, such as gears and wheels.
Another choice is to fill in the cross shape in the hub of the LEGO wheel with epoxy (see a picture of a filled in hub as used on the Hard2C robot). When the epoxy has fully hardened, a hole can be drilled that matches the diameter of the desired non-LEGO axle or motor’s shaft.
However, these techniques won’t work for LEGO wheels that lack a cross axle hole. For example, I needed a small rubber wheel for some test equipment I was building. LEGO has a compact rubber wheel that is perfect. Unfortunately, the original LEGO hub lacks a cross axle hole and is made of thin slippery plastic (so epoxy won’t stick).
I couldn’t use a LEGO motor for the test equipment, because I needed a really slow motor. Although I could have added LEGO gears to accomplish the task, it would have made for a large, complex mechanism. An eBay model-railroad engine was more suitable.
Left: Original LEGO hub with large slippery center hole. Middle: Homemade replacement aluminum hub. Right: Corresponding LEGO rubber tire. Note the molded ring in the center that mates with the center groove on the hub.
Rather than attempt to modify the existing LEGO hub, it seemed like better results would be achieved by replacing the center hub. After all, the rubber tire was the critical part I really wanted.
There are two major difficulties in replacing the LEGO hub on this particular wheel. The first difficulty is that the diameter of the hub (8.04 mm) does not match any standard off-the-shelf rod material. The second difficulty is that the hub has a groove in the center that helps hold the tire on.
The easiest way to make a replacement hub (or any other cylindrical object) is on a lathe. However, at the time, I didn’t have a lathe. Could the replacement part be made using a milling/drilling machine, grinder, and a metal file?