CHAPTER 24 ■ BODY BUILDINGTake a closer look at the diameter of the tube. Oh, no! The top diameter of the M&M’s candy tube is
slightly wider than the bottom diameter. The gearbox cover of the motor can slide completely into the top of
the tube but not into the middle or the bottom of the tube. Oh, well.
This means that one contiguous tube can’t envelop both gearbox covers across the width of the robot.
So, for symmetrical aesthetic reasons, you’ll want to cut the tube down so that only the motor portions
(not the gearhead cover portions) are contained within the tube. Notice the finished tube at the bottom of
Figure 24-13 is much shorter than the original tube, and that the finished tube consists of the wider end of
the original tube.
- From the top of the tube after the lid is removed, measure 9.5 cm and cut. Retain
the 9.5 cm piece (the one with the larger diameter) and discard the smaller end. - Midway across the tube, use the grinding-stone accessory to grind a 1-cm
diameter or slightly larger hole (see the bottom of Figure 24-13). This is where the
connectors for the motors will pass through to the circuit board. If you discover
later on that the connectors and wires are difficult to insert in this hole, feel free
to make the hole larger.
Sanding the Motor Tube
The cutting process creates burrs on the ends of the tubes. Additionally, you may not have made the cut
evenly straight across.
- With a circular motion, sand the ends of the tube with medium to fine sandpaper
to level the cut (see Figure 24-15).
Figure 24-14. Lid and rim cut off from the top of the tube