The Arduino Inventor's Guide (31 page)

Now, glue down the half of the armature mount without the drilled hole. This goes just to the left of the drinking straw, as shown in
Figure 6-21
; make sure the half with the hole is facing you when the straw is at the right. This is important so that it fits with the servo mounting arm.

FIGURE 6-21:
Gluing the armature mount to the beam

Next, bend the sides of the beam up to form a cradle that will hold the ball, as shown in
Figure 6-22
.

FIGURE 6-22:
Bending the sides of the beam to form a cradle

Use the smaller trapezoidal pieces to secure the ends of the beam and hold the beam together to keep the shape of the cradle. We suggest using a hot glue gun so that the pieces are secure, like in
Figure 6-23
.

FIGURE 6-23:
Gluing the end pieces onto the beam

Next, use the wire cutters to cut down the bamboo skewer to about 3 1/4 inches. We suggest using the blunt end of the skewer. Insert the bamboo skewer into the drinking straw to form the axle for the balance beam (
Figure 6-24
).

FIGURE 6-24:
Positioning the cut bamboo skewer so that it sticks out evenly on both sides

Now you’ll build the base of the balance beam. Score the sides of the base pieces, as shown in
Figure 6-25
, so that you can bend them into shape.

FIGURE 6-25:
Scoring the sides of the base pieces

After scoring, bend the sides to form a U shape as shown in
Figure 6-26
. Repeat this for both pieces.

FIGURE 6-26:
Bending the sides

Before gluing together the base, you’ll mount the servo motor. Remove the servo motor from the breadboard circuit. There is a small, square cutout in one of the templates that should match the submicro-sized servo perfectly. Insert the servo so that the motor is facing inward, as shown in
Figure 6-27
.

FIGURE 6-27:
Inserting the servo motor

Your servo should have come with three small screws, one short and the other two longer. Use the two longer screws to secure the servo motor in place, like in
Figure 6-28
. If you don’t have screws, you can also use a small amount of hot glue to secure the motor.

FIGURE 6-28:
Securing the servo motor in place using the two longer screws

Now, select a servo horn that’s about 0.5 inches long and single sided. Gently push this into place on the end of the servo motor, as shown in
Figure 6-29
. Once you have it securely on the servo, orient the servo to 0 degrees. Gently rotate the servo counterclockwise with your fingers until it stops. You’ll hear the little gears inside the servo turn. Make sure that you move the servo slowly; the gears are often made of plastic and can break.

FIGURE 6-29:
Attaching the single-sided servo horn

With the servo horn rotated as far as it can go counterclockwise, remove the horn and reposition it so that it is pointed straight up, as shown in
Figure 6-30
. This will make it easier to connect the linkage to the beam.

FIGURE 6-30:
Servo horn aligned at 0 degrees

Finally, secure the horn in place using the last small screw that comes with the servo to ensure that the horn does not accidentally pop out. The horn may turn as you tighten the screw. This is okay—it won’t damage anything, but you may want to hold the servo horn in place with your fingers when tightening the screw to keep the horn from rotating. If you lost the screw, it’s not a big deal; you can leave it out and just reattach the horn if it does slip out. If you have to reposition the servo arm, you’ll need to remove this screw, which is why we included a hole on the other side of the base template.

Next, you need a linkage to connect the servo horn to the beam. To make this, you’ll shape a medium-size paper clip with a pair of needle-nose pliers.
Figure 6-31
shows all the steps of this process.

FIGURE 6-31:
The steps to cutting, bending, and shaping the servo linkage