grinning mischievously at you!
After I had successfully tackled
the TCT, I decided to try to animate a
much larger prop. I crafted a spider
body out of PVC pipe with a pneumatic cylinder to raise and lower the
front of the prop (Figure 13). With
legs attached, the width was just over
20 feet! Once wrapped in black fake
fur, placed in our darkened dining
room, and revealed by a well timed
curtain drop, the spider made for a
fantastic finale for our haunted
house. See the Resources section for
a video of this prop in action.
A SIMPLE PNEUMATIC
■ Figure 13. Close-up of the 17" pneumatic cylinder used to cause the giant
spider to bounce and lunge.
So now that we're familiar with
some of the basic components of a
pneumatic system and their usage,
I'm going to walk through the creation of a simple pneumatically activated gripper using a toy robot arm
and a small double acting air cylinder. The finished gripper is actually
capable of doing simple work and is
very straightforward in design, construction, and operation.
I started with an inexpensive
plastic robot griper from a toy store
(Figure 14). I removed the handle
(Figure 15) and then using a Dremel
tool, I cut off some of the plastic arm
to reveal more of the actuator rod
(Figure 16). I then bent the actuator
rod into a Z shape (Figure 17) and
did a test fit on my pneumatic
With the arm all prepped, it was
time to create a bracket to hold the
cylinder to the arm. I used a "nibbler"
■ Figure 15. The handle and trigger
after being removed.
■ Figure 16. Cutting the end of the
robot arm reveals more of the push-rod. Remove the "holed" section to
■ Figure 17. The push-rod after being
bent into a "Z" configuration. An "eye"
has been added to the end of the
cylinder for connection to the rod.
■ Figure 14. A plastic robot arm toy.
DIY vs. Safety
While working with various home and commercial haunted houses over
the last few years, I've seen many pneumatic systems used to power props.
Some used home-brew actuators. A bit of digging on the Internet will reveal a
plethora of designs for converting non-pneumatic devices for pneumatic use.
Some of the most common are plans to convert a bicycle tire pump or a
screen door closer mechanism into an air cylinder. It's also easy to find plans
that show how to build pneumatic devices out of PVC pipe (pistons, cylinders, and air reservoirs are the most common).
Before you head down this path, take a moment to consider that using
compressed air can be very dangerous! As commercially-built air cylinders are
widely available on the surplus market at bargain-basement prices, I strongly
discourage the use of non-pressure rated or DIY devices in pneumatic systems. Not only will converting or creating an air pressure operated device
consume your time, but in many cases there are additional hidden costs in air
fittings/adapters and the like that can make the DIY device more expensive
(yet less reliable) than a commercially built unit!
If you are planning to make a device to which people may be exposed
(i.e., a pop-up scare in a haunted house), please make sure you use only com-mercially-produced cylinders and actuators to keep everyone safe!
84 February 2009
■ Figure 18. Using a metal "nibbler"
to cut an old PC cover plate into a
suitable bracket for the pneumatic