APPENDIX B ■ APPENDIX BThe finished coupler, with the set screw and cross axle, is shown in Figure B-12.Printing a 3D Wheel
What a minute! With a 3D printer we don’t need to use Lego wheels anymore. We can eliminate the separate
coupler and design a wheel that connects directly to the motor shaft.
The model follows the same principals as the coupler: start with a cylinder and subtract and add other
shapes to produce a hub with spokes. The model and the printed hub are shown in Figure B-13.
The center hole in the hub receives the motor shaft. The motor used in Sandwich includes a small flat on
its shaft, giving it a D shape. By adding a small rectangular box inside the hub center hole in the model, the
hub can also have a D shape (see Figure B-14). This prevents the motor shaft from spinning inside the hub,
even if the set screw is slightly loose. This feature is very difficult to machine conventionally, but easy for a 3D
printer.
Figure B-12. A 3D printed coupler that connects a Lego wheel to a standard motor shaft
Figure B-13. A 3D model and the finished 3D printed hub