APPENDIX B ■ APPENDIX BUnfortunately, the silicon rubber doesn’t grip nearly as well as standard rubber tires. So, I tried Plasti
Dip spray-on rubber. The hub was cleaned, then the sides protected with painter’s masking tape, and finally
the rubber was sprayed on with four or five layers (see Figure B-17).
Failed again. The spray-on rubber has a better grip than the silicon rubber, but is still not good enough.
Perhaps the thickness of the rubber is equally as important as the formulation? Also, air-filled rubber tires
seem to have better grip than solid rubber ties, so allowing the tire to flex must be important.
Compromising with a Hybrid Wheel
According to Guinness World Records, Lego is the largest tire manufacturer in the world. Lego produces
almost a million tires a day. Therefore, it seems sensible to design a wheel around their expertise.
Figure B-18 shows a Lego tire with a Lego hub alongside a Lego tire with a 3D printed hub. The printed
hub includes a D-shaped motor shaft hole to match the Sandwich motor, combined with a rim that mates
with a standard Lego tire. This eliminates the need for a coupler while still providing the benefit of a high-
quality grip.
Figure B-17. Cleaning, masking, and spraying rubber onto the rim of a 3D printed hub
Figure B-18. Replicating a Lego hub with a center hole designed to mate directly with a motor