■ FIGURE 3.
The PIR motion
■ FIGURE 2A and B. The Pop-Up Trash can is an example
of a complex pneumatic prop deployment system.
microcontroller. The Prop-1 control board was specifically
designed to be used in commercial devices and has proven
to be very robust. To allow the Prop Dropper to operate
without requiring an operator, I used a low-cost PIR
(passive infrared) motion detector as a trigger (Figure 3).
SCARE BY NUMBERS
In this month’s article, I'll walk you through making
the Prop Dropper step-by-step from hardware assembly
through wiring, and then on to software and testing. First
thing to do is get all the parts together (see Parts List). If
you have a reasonably stocked junk box, you may be able to
come up with everything you need just by digging around
your workbench. If you don't have all the parts at hand, an
entire kit of parts can now be ordered from the Nuts &
Volts website (see resources for link). Either way, once
you've gathered the parts, start with assembling the servos.
THE POSITION AND WINCH SERVOS
For the first step, get the winch servo, the position servo,
the large round servo horn, the small round servo horn,
and the wire nut together on your workbench (Figure 4).
Begin by attaching the small round servo horn to the position
servo (Figure 5). Manually rotate the servo horn so that
■ FIGURE 4. The position servo
(left) and the winch servo (right)
ready for assembly.
■ FIGURE 5. The
position servo with
small round horn
the position servo is placed at approximately 90° (i.e.,
roughly centered). This is an important step, as you want
to have the ability to move the winch servo to a straight-down position to deploy the prop, as well as a slightly
up-canted position to allow you to wind the prop back up.
Using a hot-melt glue gun, attach the small round servo
to the body of the winch servo as shown in Figure 6. Next,
mount the large round servo horn on the winch servo as
shown in Figure 7. As the winch servo has no "stop" points,
you do not need to take any precautions on pre-positioning
the horn before you screw it down. Next, use a few drops
of hot-melt glue to attach the wire nut to the center of the
large round servo horn as shown in Figure 8. Once the glue
has set, you should have a nice positionable winch assembly!
■ FIGURE 6. Hotmelt glue the position servo to the winch servo.
■ FIGURE 7. Winch servo with the
large round servo horn in place.
■ FIGURE 8. Winch servo with wire nut
glued to the center of the large round horn.
October 2009 53