The Basics of Choosing Armor
-Matt Bores

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Lacking armor in today's robotic combat cosmos is a very costly lesson to learn whether you are building in the 1lb division all the way up to the 340-390lb classes. This tutorial will outline the basic properties as well as advantages and disadvantages of several of the most popular types of armor used today.

Aluminum:

Aluminum is a very versatile material and is found on a very large percentage of robots in all weight classes. The three main alloys of aluminum used for robotic combat purposes are 6061-T6, 2024-T3, and 7075-T6.

6061-T6 is "softer" than the other two alloys and is very machineable, While 7075-T6 is the "hardest" of the three, but still machineable. 2024-T3 is somewhere in the middle of the road of the other two.

The T3 and T6 at the ends of the alloys specify their "treatment." For more in depth information on aluminum treating, visit this matweb.

The best property of aluminum, especially 6061, is that it is easy to machine. This of course is also its downfall. While it is easy to make parts out of aluminum, it is also easy for those parts to be broken by other robots. Aluminum is great for pillow blocks and motor mounts, but be careful when using it for armor because it can get very chewed up.

Carbon Fiber:

Carbon fiber is now becoming more and more popular in robotic combat, especially in the smaller weight classes. This material has a high strength to weight ratio and is extremely impact resistant. This seems to be the ideal armor for the antweight and beetleweight divisions. Carbon fiber seems best fit to these lower weigthclasses mostly due to the thicknesses that can be purchased. While it could be a great armor at 1/2 inch thicknesses for even classes up to MW, this thickness is extremely uncommon.

Caution must be taken when cutting this material and gloves should be worn at all times, as well as goggles. Face masks should be worn, and all cutting should be done in a well ventilated environment because of the harmful dust produced when machining this material. Using abrasive cutting discs can help reduce the dust, but masks should still be worn. Caution should be taken when sanding due to the strength of the fibers.

Lexan:

The true name of this material is Polycarbonate. Lexan is a trade name from the Dupont company, however it has become synonymous with all brands of the product. The material itself is simply an extremely strong, clear plastic. Lexan is very lightweight and is the same material you see used for the arena walls. Lexan can be a great material fo areas of a bot not prone to multiple impacts, or where you simply don't have the weight. In heavier bots, lexan up to 1+ inch thick can be found as armor, this material is said to be 'bulletproof' at 1/2" thick. Caution should be taken when designing with lexan. Any sharp corners can cause stress fractures which could make the entire piece crack in half. Lexan should never be tapped for the same reason. While Lexan is strong, don't expect to get away unscaved. This material will get extremely scratched because of how soft it is. It's softness can also work to your advantage as it can slow down spinning weapons and lessen the G-force of a direct hit.

Magnesium:

Magnesium is not as popular in the robot combat scene as the other materials discussed in this tutorial, but it possesses properties that make it a very good choice for baseplates and structural components in a bot. In many cases the baseplate should also be considered armor, especially in an invertibal robot. Several bots (Biohazard to name one) use magnesium baseplates to save weight over the more popular aluminum base, without sacrificing much strength or machineability.

The most popular magnesium alloy is AZ31B, and without much effort this can be found purchasable in plates or sheets. Many other magnesium alloys seem to only be found in extruded shapes. Extreme caution should be taken because this material is flammable. For special considerations when machining magnesium, visit searchwarp.

Steel:

Steel is used mostly in heavier bots for protection against high KE weapons. The post popular alloys of steel in the sport include 4130 and 4140. One thing to note about these alloys is that their usefulness as armor drastically increases if they are heat treated to the correct specifications. Machineability is good for these alloys as long as it is done prior to heat treatment. Beware, not every steel alloy is a good armor candidate. Mild steel for example is only slightly stronger than the above mentioned aluminum alloys but weighs much more and would not be adequate for use as armor in a combat robot. Another popular alloy of steel, mainly used for teeth on KE weapons, is tool steel, the most popular form is S7 tool steel. Tool steel gets it's name from the fact that it is the material used in "tools." Drill and mill bits are almost always constructed of tool steel. Some robots are ironically beginning to use S7 for protection against KE weapons. Tool steel should always be hardened to gain it's full potential, anywhere from high 40's to low 50's rockwell hardness should suffice, anything less is too soft and anything greater could end up being too brittle(drill bits for example can easily break when dropped even a few feet). Always be careful to allow tolerances on any heat treated parts. Heat treating can cause parts to warp, and if extreme tolerances are needed the parts may not fit after heat treating.

Titanium:

Titanium is well known for it's extremely high strength to weight ratio. A lot of bots in all weight classes are using it for armor. Antweights can be found sporting it in thin sheets and SHW's can be seen with thick sheets of titanium armor. The strongest grade of titanium used for robotic combat purposes is 6AL-4V or "Grade 5" titanium. A lot of full body spinners use this alloy for their shells. Other alloys are also suitable for armor but are not quite as strong as 6AL-4V. Titanium will never be as hard as hardened tool steels, but it has an extreme weight advantage. This of course comes at a sever price disadvantage. If you have the weight for steel, stell will most likely be better. If you can't afford the weight, titanium is your best friend. Because of all these reasons, Ti tends to be more popular in the lower weightclasses.

Now that a basic understanding of these materials is attained, we can put this to use. Below is a table that will rate each material and how suitable it is in each weightclass. The color band below explains the color ratings as used in the table.