Servo - September 2010

and stitch that into a band and you get tape. If you make the bi-directional fabric super lightweight, you get veil; take that bi-directional fabric and change the weave to a 2x2 or 4x4 pattern and you can get twill which easily forms around any shape. The forms of fiber are ever growing.

TTT’s robots are generally heavily built with as much kevlar as we can get our hands on as it is very light but super absorbent to impact. It can be harder to wet out and get proper lamination but it is such a wonderful material to work with because it doesn’t itch when you sand it. However, being so abrasive, it is very difficult to cut.

Carbon fiber is our next most used fabric and it is generally used for strength and stiffness in key areas. We tend to use a lot of tape forms of carbon to keep narrow segments straight. We also are guilty of using it on our final layers on the outside of the robot to give a sexy black exterior that stuns the other robots into submission.

Fiberglass is the cheapest and most readily available material, and TTT does use it heavily when we run out of kevlar or need strength and thickness. TTT also makes prototype parts with fiberglass to make sure the part will be successful before wasting kevlar, as well as using it for the molds we create for such parts. We sometimes come across remnant materials which may be specialty cloths with Mylar coatings, special weaves, or even hybrid fabrics that include carbon fiber woven with kevlar, but these materials are rare and not quite right for the average robot builder.

From bottom to top, you have a phenolic honeycomb, kevlar with a Mylar/aluminum treatment, fiberglass, carbon fiber, and finally another layer of fiberglass. All these fabrics are bi-directional. When you have your entire layup schedule together, you refer to it as a kit.

Beyond just the fabric, you then get into core materials which are designed to add thickness, insulation, structure, or form. Various types and densities of foam, honeycomb, wood, or pretty much anything that can be wet out and jammed into a laminate can be core material. Then, when you start adding resin to the mix you might have gaps or need special surfacing which may require you to add powders or materials directly to the resin before application.

Sawdust, micro-balloons (glass spheres), chopped up glass, carbon, or kevlar may be added to the resin to be used for a wide range of tasks. The beauty of composites is the flexibility of not only the standard laminate, but the array of materials in which you can use them.

Max Bond epoxy system from Polymer Composites, Inc. This would be the marine grade resin two gallon kit as purchased through eBay or directly through the company. It is a 1:1 ratio mix of part A and part B.

There may be a lot of information about various fabric materials that can be used successfully in combat robots, but as far as resins go there is one clear winner: epoxy. Polyester, vinyl ester, phenolic, polyurethane, and bismaleimide resins just aren’t quite capable of being what epoxy is. Epoxy may be a bit more expensive, but you just can’t beat its strength and ease of mixing without using dangerous catalysts.

Most epoxy types have a standard two part system, but make sure you read the exact ratio of hardener to epoxy as per the manufacturers instructions (as well as the MSDS). We have used various epoxies at various price levels and have found a lot of epoxy manufacturers put plastesizers and sometimes just a whole lot of junk that adds nothing to the strength of the resin but merely increases the volume.