CHAPTER 20 ■ COUPLER
Matching wheels screw onto the hubs. The wheels are available in a variety of sizes and colors. The
two-inch diameter acrylic wheels (#59571for $3.99) and two-inch diameter foam wheels (#2TMD for $16.95)
are the correct size for Sandwich. The wheels come in pairs, so don’t make the mistake that I did by buying
two of them (because you’ll end up receiving four wheels).
Making Couplers If You Have Metal-Working Equipment
If you have access to a lathe or a milling machine, you may want to consider an alternative to the instructions
in this chapter. In fact, a lathe is the perfect machine to produce the highest-precision metal LEGO couplers.
Instructions are posted at http://www.robotroom.com/LatheCoupler.html.
For readers with a milling machine, Chapters 3 and 4 of Intermediate Robot Building by David Cook
(Apress, 2010) provide complete instructions.
Printing Couplers
Better still, check out Appendix B for instructions on printing the LEGO coupler on a 3D printer. The printed
couplers are designed to match the shape of the LEGO cross axle and the flat on the gearmotor shaft. Thus,
the printed couplers require no adhesive and are less likely to come loose during operation.
The printed couplers still require tapping a hole for a setscrew, so it is worthwhile to at least read that
section of this chapter.
Tubing
At this point, let’s assume you’ve decided to make the LEGO couplers using the instructions in this chapter.
The first step is to acquire the raw material.
The coupler consists of a metal tube. One end of the tube has the appropriate inner diameter to accept
a standard LEGO cross axle. The other end of the tube has the appropriate inner diameter to accept the
selected motor’s shaft. The LEGO axle is permanently glued to the coupler, but the motor shaft is held in
place by a screw to allow for disconnection.
Figure 20-1. The set-screw hub (first motor) and clamping hub (second motor) connect the motor shaft to a
ready-made wheel (right)