now open without restraint. Build a speaker box with 1/4”
balsa wood, but keep as much room behind it as possible.
You must have enough room behind it to fit the circuit
board to the ‘floor’ of the box. Mount the 2” speakers and
put a grill (3D printed or screen) over them to protect
against pokey fingers.
This enclosure for the speakers has much better bass
response and increases volume. Bring the speaker leads
through the back of the balsa box to be attached later to
the PCB Next, mount the standard servo in a bracket that
brings it near — but not above — the cover. The bracket
can also be made of wood or be 3D printed; see Figure 7.
Lightning is accomplished with white high-brightness
LEDS driven from the microprocessor through an N-channel
FET. Connection to the LEDs is shown back in Figure 3.
I printed the gums, the nose, servo brackets, servo
arms, and the speaker grills on my 3D printer; if you have
a 3D printer, the files are on Thingiverse.com under the
name welwell. I treated the outside of
the plastic with acetone to make it
shiny for the gums and nose. Don’t
worry if you don’t have access to a
3D printer. The first Monster book
was built without one. Plastic parts
simply make it easier. The gums and
nose can be made with polymer clay,
but try to keep the weight low on the
cover; maybe put a thin coat over
Styrofoam. Nasty-looking sharp teeth
are made with OOGOO: a
homemade concoction made with
one part type 1 clear silicon caulk and
two parts corn starch. Once mixed
and let set up for five minutes, you
can shape the teeth with your hands.
These teeth can hold their shape well,
but are very flexible in case a small
hand gets in the chomping monster
jaws. Make the teeth, let them cure, then glue them in
with fresh OOGOO. OOGOO formulations are found at
www.instructables.com/id/How-To-Make-Your-Own-Sugru-Substitute. Refer to Figure 8.
Monster Book Mechanics
Just about any standard servos will work, but the lid of
the book becomes heavy with components and fur, so
one standard servo with bearings is preferable to lift the
cover (jaw) quickly. The eyes and eyebrow servos (micro)
should be light weight, so that weight is reduced on the
cover of the book. There are three servos used: one to
move the cover, one to move the eyes left/right, and one
to move the eyebrows up/down.
Cut two 3” steel rods to act as the eyeball pivots. Drill
the cover with two 1/8” holes located 2-5/8” apart and
centered side-to-side, about 3” from the back ‘binding.’
Put wheel collars on each rod at the very end and push
them through the holes in the cover. Drill a small hole in
the back of the eyeballs to accept the ball of a ball link,
and glue it in. Then, place one more wheel collar against
the top side, then the eyeball, then another wheel collar.
Reinforce the steel rod to the book with epoxy, being
FIGURE 10. Eyeballs
linkage and servo
SERVO 10.2014 57
FIGURE 9. Unibrow servo placement.