then I drilled and tapped additional
holes to connect the blade to the
gear. Volià! A sturdy hub
to mate the two objects
together.
After some decorations, the robot named
“Pacman” was ready just
in time for the competition. While it was not
the best, it was a
favorite to the audience, as they
chanted “Wakka wakka wakka!”
Pacman charges up his blade
and tests his metal against
the titanium tank Fir Darrig.
Photo by Kevin Berry.
when Pacman was called to
compete. The serpentine belt
system worked like a charm, the
robot drove with great control, and
I was relieved to know that I had
survived the two-day gauntlet with a
record of five wins and two losses.
Robot building is similar to
school work. There are deadlines,
there are excuses, and there are
lessons to be learned in both. Just
remember your robot building basics
and there will be no pressure when
your robot is due! SV
MAN UFACTUR IN G:
RioB tz Combat Tutorial
Summarized — Materials
● Original Text by Professor Marco Antonio Meggiolaro; Summarized by Kevin M. Berry
Professor Marco Antonio Meggiolaro of the Pontifical
Catholic University of Rio de Janeiro,
Brazil, recently translated his popular
book, the RioBotz Combot Tutorial
into English. In June and July,
SERVO summarized Chapter 2,
“Design Fundamentals.” This month,
we continue the series with a
summary of the first part of Chapter
3, “Materials,” focusing on
commonly used metals in combat
bot building. Marco’s book is
available free for download at:
www.riobotz.com.br/en/tutorial
.html, and for hard copy purchase
— at no profit to Marco — at
www.lulu.com/content/7150541.
All information here is provided
courtesy of Professor Meggiolaro
and RioBotz.
Mechanical Properties
There are several terms needed
to understand the properties of
materials. Most materials start off
deforming in an elastic manner,
meaning they spring back after
being bent. This is dependent on
the stiffness, or “Young Modulus.”
After some point, the elasticity is
lost. The material begins to yield,
meaning it no longer springs back
to its original shape. This is called
“plastic deformation.” It continues
yielding (bending) until it reaches a
value called the ultimate strength,
where it breaks. Ductility is another
term related to how well it deforms
without breaking, related to the
above terms in a way requiring a
lot more explanation that we can
do here.
The above values are usually
tested in a slow manner. Dynamic,
or “fast” loads use the terms
resilience and impact toughness.
Resilience is how much impact
energy it can take before it starts to
yield, or bend. Toughness tells how
much impact energy it absorbs
before breaking.
How do we use this information? A tough material is not
necessarily resilient, and vice versa.
For instance, the stainless steel (SS)
type 304 — the most used SS —
tolerates large deformations but it is
easily yielded. It is very tough, being
good for armor plates that can be
deformed. However, it has low
resilience, and thus it should not be
used in shafts (which should not get
bent or distort) or in wedges
(because if their edges are bent or
nicked they lose functionality).
On the other hand, the steel
from a drill bit, for instance, is very
hard, with a very high yield
strength, and thus it has a high
resilience. However, its impact
toughness is low. This is why drill
bits do not make good weapons for
combat robots, because they easily
break due to impacts. Titanium is an
excellent choice for use in combat
robots because it is very tough
(good for armor) and resilient (good
for wedges) at the same time.
Fracture toughness is another
useful term which means how well
it resists propagation of cracks. This
is related not only to the material
itself, but the geometry of the
actual piece being used. Thinner
plates, for example, can deform
26 SERVO 09.2009
