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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 . . .



Cutting
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.



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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.



Sandpapering
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
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.

Glueing
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.

Making Styrofoam
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)


Buna-N (Nitrile) Excellent oil resistance, and good protection from impact, abrasion, and oxidation.	Butyl Excellent resistance to oxidation and electricity, and good resistance to ozone, abrasion and tearing.
EPDM Excellent protection from degradation from sunlight, ozone, and electricity. Good resistance to impact, abrasion, and tearing.	Epichlorohydrin (ECH) 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.
Hypalon Perfect for outdoor applications. Excellent resistance to weather, oxidation, ozone, abrasion. Good oil, acid, and flame resistance.	Hytrel� 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.
Melamine Foam 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.	Neoprene Excellent abrasion and oxidation resistance. Good oil, electrical, flame, impact, tear, and weather resistance.
Polyester Washable, moisture-resistant, fire-retardant foam. Hundreds of small pillows per foot keeps items firmly in place. Made from vinyl-coated polyester scrim.	Polyethylene Lightweight, cushioning, and absorbant. Excellent chemical and moisture resistance.
Polystyrene Lightweight and formable foam. Closed-cell structure will not absorb moisture. Sheets can be cut with a razor knife.	Polyurethane 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.

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