Page 208 - Build Your Own Combat Robot

Robot Material and Construction Techniques
Chapter 9:
used to solder small brass pieces together, but these should not be used in high- 189
strength areas or where shock may be present.
Many hobby shops carry miniature brass extruded sections in 12-inch and 36-inch
lengths that are great for small robot construction. They come in square, rectangular,
hexagonal, and round tubes that fit closely within each other for telescoping applica-
tions, as well as channels, solid sections, and sheet stock. Sizes vary from 1/32 to
about 1/2 inch. Note, however, that brass has a poor strength-to-weight ratio, and is
therefore not a good choice for most combat applications.

Titanium

Titanium is finding more use in combat robots. Though “heavier” than aluminum
at a ratio of 1.7:1, it does not really compare with aluminum—or any other metal,
for that matter. Long used by the military for lightweight armor and jet engine
parts, it is finding uses for consumer applications such as combat robots. It melts
at a temperature of almost 1000 degrees Celsius higher than aluminum, and can
withstand deformation and bending much better than that alloy or most steels. Its
main drawback is its extremely high cost and difficulty to machine and form, but
it is becoming more popular for so many uses that the cost is dropping rapidly.
Titanium alloy 6AL-4V is a general-purpose, high-strength metal that is avail-
able in round bars and flat sheets. As with all titanium alloys, it requires patience
in machining. Ample lubricant and slow feed speeds are necessary. The 40,000
psi yield strength alloy is an easier-to-machine alloy. Each can be found in
lengths of 3 and 6 feet, and diameters from 1/8 to 2-1/2 inches.

Using Extruded Metal Stock for Robot Structure

In discussing the many types and alloys of metals available for robot construction,
we mentioned the many forms in which the metal is available. Careful thought in
design can make use of these forms not only to add to the structural integrity of the
robot, but to simplify the construction. Co-author Pete Miles made use of a wide
piece of aluminum C-channel stock to form the sides of his robot Live Wires. This
heavier piece of preformed metal not only offered much greater side strength from
possible puncture by an opponents weapon, but it offered him a simple and secure
way to fasten the upper and lower plates to form the overall structure. Figure 9-1
shows how C-channel extrusions can be used as external robot structures.
The most common form of extruded structural shape is the angle, or L-shaped,
piece of metal. These shapes can be used in two different ways to achieve a stout and
robust structure for your robot. Each of the sides of the robot’s frame can be con-
structed of pieces cut to form the edges. If either of the metals is to be welded, indi-
vidual end welds will not have sufficient strength without the help of a “gusset”
welded into the corners. These triangular pieces of metal add tremendous strength
to the overall structure. Figure 9-2 illustrates a simple gusset arrangement.