of its high stiffness. It is a myth that
carbon fiber has high impact toughness, though. It surely has a high
strength under static loads, but it
does not take severe impacts.
The undercutter Utterly
Offensive is a good example of that;
its carbon fiber baseplate (see
photo) self-destructed when it was
scraped by its own spinning blade.
The plate was later switched to
titanium. Carbon fiber is not a
good armor material, unless it is
combined with Kevlar to achieve
high impact toughness.
There are several other
composites that use a polymer
matrix (such as epoxy or polyester)
besides plain GFRP, KFRP, and CFRP.
For instance, you can tailor lay-ups
of aramid and carbon fibers cured
(bonded) together with a polymer
matrix to achieve optimum impact
toughness (due to Kevlar) and
stiffness (due to carbon).
It is possible to generate
complex unibody structures by
combining several parts into a single
cured assembly, reducing or even
eliminating the need for fasteners
and saving weight and assembly
time. One technique is to use
adhesive bonding where composites
or metals are bonded to other
composites, honeycomb cores foam
cores, or metallic pieces.
An example is where a
rigid unit is made with a poly-methacrylimide foam core,
sandwiched by CFRP sheets (see
photo). Besides increasing the panel
bending stiffness, the foam core
also works as a shock mount,
increasing the impact strength. It
also becomes a good option for the
robot structure and even the armor.
An even the higher stiffness-to-weight ratio can be obtained if the
core is made out of balsa wood, as
shown in the photo of DragonPlate.
However, its impact toughness is
We use a Kevlar/Nomex honeycomb material, purchased from
in all of our insect class bots, and
have several sheets up to 1” thick
we plan to use in bigger bots. It has
proven extraordinarily effective
against spinners. Babe (see photo)
spent a whole event giving spinner
rides with minimal damage).
Professor Marco notes that,
while these composites are tough,
a metallic overlay such as the
titanium side panels on Babe
significantly increase long-term
Metal Matrix and
Instead of having their fibers
embedded and held together in a
polymer matrix, these composites
use either a metal or a ceramic
matrix. The fibers (or even tiles in a
few cases) can also be made out of
metal or ceramic, which tends to
increase the ultimate strength and
stiffness of the matrix material.
However, most ceramic matrix composites have low impact strength,
which limits their use in combat —
not to mention their very high cost.
On the other hand, when part
of a multi-layer composite armor
plate such as the Chobham armor,
ceramic tiles embedded in a metal
matrix can be very effective to shatter kinetic energy weapons. SV
Completed and Upcoming Events
Completed Events for
July 16 to Aug 15,
PA Bot Blast 2009 was
held July 18th in Bloomsburg,
PA. Twenty-seven robots were
Upcoming Events for
Franklin Institute 2009 will be presented by North East
Robotics Club in Philadelphia, PA
October 4th and 5th. For more
information, go to www.nerc.us.
Mecha-Mayhem 2009 will be
in Rosemont, IL October 23rd
through 25th. For more information,
go to www.theCRCA.org.
Robothon Robot Combat 2009 will be presented by Western
Allied Robotics in Seattle, WA
October 11th. For more
information, go to www.western
32 SERVO 10.2009