Page 121 - Robot Builder's Bonanza

90 WORKING WITH PLASTIC

The Ins and Outs of Rigid Expanded PVC

Rigid expanded PVC is the robot maker’s dream material, and I use it extensively, more than
any other type of plastic. Figure 9-2 shows a prototype robot made using 1/4″-thick expanded
PVC plastic.
Rigid expanded PVC is commonly used for sign making, so it’s relatively cheap, light-
weight, and available in a rainbow of colors. It’s manufactured by mixing a gas with molten
plastic. The plastic is then extruded into various shapes: sheets, rods, tubes, bars, and more.
The gas forms tiny microscopic bubbles in the plastic, expanding it. The expansion makes the
material bulkier— and therefore lighter. Because of the rough, bubbly appearance of the plas-
tic, expanded PVC is sometimes referred to as “foam PVC” or “foamed PVC.”

BENEFITS OF EXPANDED PVC
Rigid expanded PVC comes in all sorts of shapes, sizes, and colors, but it’s the sheet form we’re
most interested in. Because it’s been “puffed up” in the expansion process, expanded PVC
contains less plastic than ordinary PVC materials. The benefits of the expansion process are:

• Less plastic = less weight. That’s important for building robots where added weight makes
the battery drain faster.
• Less plastic = less density. This makes expanded PVC easier to drill, cut, and mill. If
you’ve ever cut acrylic plastic, you know it chips and breaks easily, and its high density
makes using hand tools a real chore. The thinner expanded PVC materials can be cut using
a knife; the thicker stuff, with an ordinary saw blade.

Rigid expanded PVC (or simply PVC from here on) is often used as a replacement for
wood. As robot builders, we’re more interested in the PVC sheets used to make signs— sign

Figure 9-2 With its ease of drilling
and cutting, expanded PVC plastic lets
you create all sorts of designs for your
robots. This one uses two “decks” or
levels that are merely rectangles with
the corners cut off. The robot is
completed using brackets for the four
servo motors.

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