Nuts and Volts - February 2009

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 GRIPPER

■ 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 cylinder.

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 increase durability.

■ 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!