CHAPTER 20
Coupler
A coupler connects two things together. This chapter consists of step-by-step instructions for making a
coupler that, in this case, connects the selected gearhead motor’s shaft to a LEGO cross axle. The general
nature of this coupler is applicable even if you choose a different motor or a different type of wheel.
A coupler is needed because the shaft of the chosen motor is neither the correct shape nor the correct
size to accept a LEGO wheel. Even if glue or solder could adhere them together, the robot would probably
need to be disassembled or experimentally modified at some point. This would rule out permanent
adhesion of the wheels to the motors. The coupler presented in this chapter makes it easy to remove or
change wheels at any time.
The line-following robot has two wheels. It needs one coupler for each wheel. Therefore, the robot
needs two couplers in total.
Alternatives
These instructions require some light machining with a handheld rotary tool. Most beginners are
uncomfortable with machining or metal-working tools. Initially, so was I!
Yet, one of the most fascinating and enjoyable aspects of robotics is creating your own custom body
parts. I highly encourage you to at least attempt the relatively simple coupler project in this chapter. It may
open your heart to the human-ingrained discipline of physically working with tools.
Buying ready-made parts instead of making a coupler, you can purchase a motor and wheel that are
designed to fit together. For example, Chapter 18 suggests the Solarbotics “#GMPW Deal” motor and wheel
combination.
If you prefer the Hsiang Neng motors, ServoCity.com sells several different types of ready-made
mounting hubs and matching wheels (see Figure 20-1). The motor has a 4 mm shaft. Therefore, buy either
a pair of the 4 mm Bore Set Screw Hubs (545568 for $4.99 each) or a pair of the 4 mm Bore Clamping Hubs
(545608 for $7.99 each). The clamping hub is a superior design that holds onto the motor shaft more securely
and does not mar the shaft, but it is more expensive.