MATERIALS - STYROFOAM
Styrofoam is probably the most overlooked material for robots.
This is mostly because of the general public's misperception that it has low strength and high wear. However,
with the right methods and materials, styrofoam can easily rival balsawood
as a lightweight effective construction material.
First, there are many types of styrofoam. Packing foam for example is generally
low grade. It is designed to be shock insulation only. What you want is a higher
grade styrofoam, one with rigidity. What I will be referring to as styrofoam is a foam core type.
Foam core, most commonly used for home insulation, comes typically as a bright pink or grey color.
These types of foams can be shaped into almost anything. In the design industry, foam is the material of
choice for rapid prototyping, but they can also be used for robot boats and even robot wings.
Styrofoam can float, is very light weight, can be made into any shape, and can actually be high strength if made into a well
designed shape. It is also great for shock and vibration absorbance. Dont forget you can also put wooden inserts
into foam as structural support.
However styrofoam should never be used for precision applications - obviously.
Styrofoam has some give to it, even the more rigid types. But for other applications that can be an advantage.
Non-rigid materials are resistant to vibration. Styrofoam works as a great thermal insulator too.
A side note, do not place robot motors into styrofoam as they poorly conduct heat away. I once fried a motor
trying doing this . . .
Working with styrofoam is very easy. Styrofoam cuts easily with a serrated knife, hacksaw, floral knife,
cookie cutter, or X-acto® knife. But make sure you only use a fresh extremely sharp blade, or you
will not get clean cuts in the styrofoam. A cutter, where you break off old sections of the blade, work
quite nicely. You should use a new blade about every 8 cuts or so. Yes, that sharp.
Also try waxing the knife blade with an old candle for easier, smoother cuts. To cut a thick piece of styrofoam, or several
sheets stacked together, try using an old electric knife, bandsaw, or scrollsaw.
You should also aline your cuts with a ruler. Drill presses are great for making holes.
Hot Wire Cutting
Hot wire cutting is fairly straightforward. Get a long metal wire, apply power to it so that it heats up bright red,
and move foam across it. Basically like a hot knife through butter. You will probably need to buy a special
Hot Wire cutting wire (the google ads above usually have them). Use a
lead-acid battery or a power supply, perferably one with adjustable controls.
Use aligator clips to power the wire. Use a rigid mount to hold the wire taught (straight and stiff).
A hacksaw without the blade (and insulated from the hot wire) would make a great mount. Apply current and raise
the voltage until the hot wire starts turning redish. Not too hot or the wire may break or your clips might melt.
It will take a little practice, but you can get clean perfectly straight cuts with the hot-wire.
Sanding your styrofoam is great for precision shaping, rounding, and smoothing. After cutting to the basic shape you want,
use a rough type sandpaper for the larger changes, and a finer sandpaper to get that professional finish on your part.
Use an extremely fine grain sandpaper for a really clean finish (assuming you are also using a high density foam).
You can also 'sand' styrofoam with other pieces of styrofoam if you do not require perfection.
Painting can give your styrofoam environmental wear protection or just make your robot look cooler.
For rapid prototyping or modeling, if you put a shiny paint over your foam, it would actually look like a solid
plastic part. Very proffesional looking.
Details on painting . . .
Paint with an acrylic craft paint.
Solvent-based paints may damage the foam (see paint manufacturer's instructions for details).
For thorough coverage, try a stiff stencil brush and gently "scrub" the surface with the paint. Or, place the foam shape and
paint in a zip-lock plastic bag, seal the bag, and rotate it until it's completely covered. Remove from bag with
pick and let dry. Spray paints are usually work on styrofoam - read the label carefully to
determine whether or not it's foam-approved. For easier handling when painting,
insert a floral pick or skewer into the foam shape to use as a handle. When done, insert
the handle in a block of styrofoam or stand in a cup or something while paint dries.
For a fast bond, use a low-temperature glue gun (if too hot the foam will melt).
Elmers glue works. For a better bond between two pieces, insert toothpicks between the pieces to
hold them together while the glue dries. Toothpicks can also be used as structural reinforcment.
Texturing and Shelling
If you are an engineer, but an artist at heart (no comment), you can texture your foam too.
Cover your styrofoam with plaster, wallboard compound, gesso, modeling paste or other coating materials.
Then just swirl, shape, or sculpt it or whatever. This is a great way to improve the properties of your foam too.
If you add a thin protective shell around your foam, you have an extremely light weight very strong material.
I have often seen this method for making model buildings and fake rocks - very useful if your a board gamer
(for like Warhammer), an archetect, or a sculptor.
Suppose you didnt want to work with pre-fabricated pieces of foam, but instead wanted to make your own foam
for casting or filling a mold. To do this, you can buy off-the-shelf foam culking - the stuff they use
to fill cracks in window frames, or other such housing insulation projects.
It easily sprays out of a can, and over time expands ~5x to fit any mold as a solid block of tough foam.
Its clean, cheap, and simple. And a lot of fun to play with, too =P
This expanding spray foam insulation is made from just two mixed liquid chemicals (of which I dont know off hand),
but if you have an especially large project, buying the chemicals and mixing it yourself will be the cheapest/easiest option.
Purchasable kits are also available, for your specific needs.
Types of high grade foam core:
(all can be bought at mcmaster.com)
Excellent oil resistance, and good protection from impact, abrasion, and oxidation.
Excellent resistance to oxidation and electricity, and good resistance to ozone, abrasion and tearing.
Excellent protection from degradation from sunlight, ozone, and electricity. Good resistance to impact, abrasion, and tearing.
Excellent resistance to oils and gasoline. Good resistance to electricity, abrasion, weather, ozone, and oxidation.
EVA (Ethylene Vinyl Acetate)
Highly resilient, closed-cell foam. Extremely light in weight. High tear strength and good compression set resistance. Thermoformable.
Extreme-Temperature Polyimide Foam
Low-density, open-cell foam. Emits virtually no smoke or toxic by-products when exposed to flame.
Perfect for outdoor applications. Excellent resistance to weather, oxidation, ozone, abrasion. Good oil, acid, and flame resistance.
The flexibility of rubber and strength of plastic. Resists tears, abrasion, and corrosion. Often used in protective apparel and wire and cable jackets. Excellent resistance to oils, fuels, and chemicals.
Perfect for ducting, tanks, and slightly curved surfaces. Lightweight sheets with porous open-cell structure that absorbs moisture. Can be cut with razor knife and installed with adhesive tape or mounting hardware using washers.
Excellent abrasion and oxidation resistance. Good oil, electrical, flame, impact, tear, and weather resistance.
Washable, moisture-resistant, fire-retardant foam. Hundreds of small pillows per foot keeps items firmly in place. Made from vinyl-coated polyester scrim.
Lightweight, cushioning, and absorbant. Excellent chemical and moisture resistance.
Lightweight and formable foam. Closed-cell structure will not absorb moisture. Sheets can be cut with a razor knife.
Lightweight. Smooth-finish. Ranges from very soft to very hard. Better cut, tear, and abrasion resistance than other elastomers. Also resists breakage on impact, water, oxidation, ozone, and many solvents. Nonbrittle. Returns to original shape. Extremely stable through temperature changes, but not recommended for prolonged steam contact.
Super-Tough Ionomer Foam
Strongest, most durable foam available. Low density. Excellent tear strength, impact resistance, and abrasion resistance. Good flexibility. Virtually unaffected by ultraviolet rays, freezing conditions, and other weather extremes.