■ FIGURE 9. Drilling a hole where
the string to the prop can be
■ FIGURE 10. A temporary bracket created from an old PC card back plane,
glued to the position servo.
■ FIGURE 11. The Prop Dropper in
place with a prop wound up and
ready to drop.
At this point, you need to drill a hole in the large
round servo horn to allow you to attach the string that
connects to the prop (Figure 9). For testing, I fabricated a
temporary hanging bracket using an old PC back plate
that I glued to the back of the position servo (Figure 10).
I then attached a small rubber bat to the large round servo
horn and hung the completed assembly from the ceiling in
my shop for testing (Figure 11). A video of the Prop
Dropper in action is available online (see resources).
motion detector, be sure to watch the polarity of the plugs
to make sure the white lead is connected to the "W" pin of
the jack. The pins are clearly labeled at the top of the
Prop-1 with W, R, and B to help guide you.
WIRE IT UP
Strangely for an electronics project, the wiring for this
device is one of the simplest steps! The EFX-TEK Prop-1
controller makes it a literal matter of plug-and-play — there is
no soldering involved in assembling this entire project. To
illustrate, the schematic is shown in Figure 12 and a photo
of how the servos and motion sensor are attached is shown in
Figure 13. (Note: This simple assembly process makes the
Prop Dropper an ideal project to share with youngsters!)
Following the schematic, plug the winch servo into
the P0 header, the position servo into P1, and the motion
detector into P7. When connecting the servos and the
■ FIGURE 12. The
Now that we're all wired up, it’s time to get familiar with
the software. The basic software used to operate the Prop
Dropper consists of a single loop with one decision point in it.
The flow chart is shown in Figure 14. Following the flowchart,
you can see we begin by waiting in a loop for the input to be
triggered. Once a trigger has been detected, we send pulses
to the position servo that causes it to move the winch servo
to its "pointing down" mode. This causes the string to fall
off the end of the wire nut and allows the prop to drop.
Next, we wait a bit while the prop dangles in the air, then
send pulses to the position servo to position the winch servo
pointing up to the retrieve angle. Once the retrieve angle has
been reached, we send pulses to the winch servo to cause it to
wind the string back up. The amount of time the winch servo
runs is based on the length of the string, i.e., longer string =
more wind time. Once the winch servo has retrieved the prop,
we then pause for a bit to keep the prop from being
prematurely re-triggered immediately after deployment.
DOWNLOADING AND TESTING
You can download the source code for this
■ FIGURE 13. The Prop
all wired in place.