APPENDIX B ■ APPENDIX B
The outer dimensions of the original Lego hub were measured using a digital caliper. Figure B-19 shows
how well these details are reproduced. The inner spokes and D-shaped motor shaft hole were copied from
the previous attempt at making a wheel. The ability to copy and rework designs is a huge benefit of 3D
printing.
Designing a Robot Body
A large part of Sandwich’s appeal is its container. However, using a container designed for lunch and
leftovers requires grinding, drilling, standoffs, and fasteners. As illustrated earlier in the chapter, a purpose-
built shell can include a battery compartment and mounting holes molded into the base.
The 3D printed Sandwich body went through numerous generations as I became more proficient
in modeling and printing. In Figure B-20, notice the how much the 9V battery compartment changes
orientation for better balance and retention. Also, the design includes labels, such as “Sandwich” and “9V”,
but transitions from cutouts to raised letters for strength. Sharp corners and slots give way to curves and
holes.
Figure B-19. Matching the dimensions of an industrial-molded Lego hub on a 3D-printed hub
Figure B-20. A progression of design improvements on the 3D printed Sandwich robot platform
To increase rigidity, a rib is included and standoffs are tapered where they meet the base
(see Figure B-21). The front lip is beveled to avoid snagging on cracks on the line-following track.