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Beyond Metal, Plastic,
Plikely it’s made of one of three
materials: metal, plastic, or
ick a robot — any robot — and
wood. And little wonder — these
three groups of materials are used
in the vast bulk of products today.
From houses to cars to the chair
you’re sitting in, very likely it’s made
with metal, plastic, or wood, or a
combination of these.
Just because these are the most
common construction materials
doesn’t mean they are the only kind.
There are also various kinds of foams,
cardboard, unusual wood-based
products, and even clays that can be
used to build robot bodies. True,
many of these are merely sub-types
of wood, plastic, or metal; cardboard
is made of paper, which is a wood
product, and polymer clay is a type
We aren’t going to split hairs
here. It’s the function and design of
the material that’s most important.
These unusual materials — either
because of the way they are made or
how they are constructed — exhibit
properties not typically found in
the average sheet of metal, plastic,
So-called construction foams are
popular at many craft shows where
they are used to make a variety of
homemade projects. Some intrepid
robot builders have picked up on the
idea and use them in various ways to
make or reinforce their bot bodies.
Construction foam was originally
intended to be used in buildings
for sub-flooring, insulation, and
sound-proofing. This material is
commonly referred to as “blue foam”
and represents a rather diverse family
of molded expanded polystyrene
(MEPS) plastics. Blue foam is more
rigid than fiberglass insulation and has
a higher R factor (R factor is the rating
for insulating materials).
Blue foam is from one to three
inches thick, though specialty versions
are available in thinner sheets. This
latter material can be found at
One particularly useful application
of blue foam in robotics is as a
substrate or “rigidizer.” It weighs very
little for its size and bulk, yet offers
remarkable rigidity. Rather than use a
thicker piece of metal, plastic, or
wood, you instead glue a square of
the foam to a thinner sheet. The
combination provides increased
rigidity, but not at the expense of a
lot of unneeded weight. It’s best
used when physically cemented to a
sheet, such as 1/8” (or even thinner)
plywood or plastic. Being foam, it’s
easy to saw or drill, but it does break
off into pieces the way Styrofoam and
similar materials do.
Though called blue foam, its color
may be either blue or pink or even
some other color. The foam is
available in different densities, with
many of the pink variety foams having
the lowest densities. You may find the
heavier blue foam easier to work with
because it’s not as floppy.
The one drawback to construction
foam is that it adds some bulk to your
robot, but you can use this to your
advantage. For example, if you’re
constructing a robot for use around
the home or garage, you might place
panels of blue foam bonded to very
thin styrene plastic sheets to act as
the sides of your bot. Position the
foam on the outside and it’ll act as a
kind of cushion, protecting the fragile
innards of your mechanical beast and
hopefully sparing the furniture and
people it runs into.
Foam board is part foam, part
paper. It is available from art supply
stores in thicknesses from 1/8 to over
1/2 inch. Construction is simple: an
inner foam sheet is sandwiched on
both sides with high quality paper.
Foam board is cheap, easy to cut
with a hobby knife or small scroll saw,
and can be readily glued.
You can provide extra rigidity to
foam board by combining it with
another thick substrate such as
cardboard, thin metal, or plastic.
However, depending on thickness and
weight loads, foam board can be used
by itself. Foam board is often referred
to as Foam Core — a commonly used
brand. It’s available at any art supply
store and many crafts outlets.
One application of foam board is
creating test bases for your robots.
Using just a knife, you can easily
cut and drill different sizes and styles
of bases to test various designs. It