CHAPTER 24 ■ BODY BUILDINGNeeding Washers
You could drive the screw until the screw head is completely pressed against the container wall. But then, all
of the forces acting on the motor and wheel would be exerted on a tiny, thin area of plastic. After the robot
has a couple of solid hits against a wall or chair leg, one or more screw heads may rip through the plastic
wall, ruining the robot body.
Washers are flat discs with holes in the center (see Figure 24-11). By inserting a washer between the
screw head and the container wall, the forces are spread out across the surface covered by the washer. In this
way, washers provide added strength to the location under the most stress.
Because of the thin plastic throughout the container, all screws on Sandwich have nylon washers added
to them. You can purchase 100 nylon #4 screw size flat washers for $5.50 from Digi-Key (part #3158K). These
washers are 0.047-inch thick.
- Add one washer to each screw if you obtained 6-mm long screws. If you’re using
8-mm long screws, add three washers to each screw (see Figure 24-12) since the
motor holes aren’t deep enough to drive the 8 mm screws in all the way.
Figure 24-11. Four M2.6 x 8 mm screws with three nylon washers each
Figure 24-12. Test fit of motor with screws and washers
- Test both motors to see that they fit in the container holes and that the screws
and washers hold the motors firmly in position. (Don’t forget to remove the
motors before drilling any more holes in the container.)