CHAPTER 24 ■ BODY BUILDING
- Eight #4 screw-size nylon flat washers (same washers as used on the motors)
- Four 1-inch long spacers
See Figure 24-26 to get a look at them all.Figure 24-26. Four #4-40 1½-inch machine screws with two #4 washers each (top), four hex threaded
standoffs (middle), four #4-40 nuts with integrated external-tooth lock washers (bottom)
Selecting and Obtaining Spacers
Spacers position the line-following circuit board away from the container so that the Molex connectors can
fit in the space in between. Additionally, the spacers position the circuit board about 20 cm from the floor,
giving the sensors ample, nearby views of the line to follow.
Shorter-length spacers are commonly used on computers, stereos, and other products with circuit
boards to allow airflow on both sides of the board for heat dissipation.
Hex (six-sided) threaded spacers, like those shown in Figure 24-26, have holes with screw threads that
grip the #4-40 screw. These types of spacers, with threads or integrated screws, are often called standoffs.
The thread’s grip on the screw reduces rattle and permits the circuit board to be removed without the screws
and standoffs falling out. Unfortunately, some of the longer threaded spacers are not threaded all the way
through in the very center, which must be laboriously corrected with a tap.
Round thru-hole spacers are also available. Sometimes they’re called “clear” spacers or “non-threaded.”
Not only are they less expensive than the threaded variety, but also they have the advantage of simply
slipping onto the screw without all the effort of turning them (no threads). But, of course, they fall off just as
easily when the nuts and circuit board are removed.
To compromise, you could select two ½-inch spacers, one threaded and the other thru hole. Put the
thru-hole spacers on first and then add the threaded spacers to the ends to keep everything in place.
Aluminum, nickel-plated brass, and ceramic spacers are common. But nylon is cheaper and lighter.
Table 24-1 lists suppliers of various lengths of nylon spacers.