MAN UFACTUR IN G:
RioBotz Comb t Tutorial
Summarized:
Design Fundamentals
● Original text by Professor Marco Antonio Meggiolaro; Summarized by Kevin M. Berry
Professor Meggiolaro of the
Pontifical Catholic University
of Rio De Janeiro, Brazil, recently
translated his popular book,
The RioBotz Combot Tutorial, into
English. In the process, he greatly
expanded it and solicited input
from a wide range of robot
builders. The updated version — 367
pages long with an incredible 895
figures, graphs, and photographs —
is available free for download at
www.riobotz.com.br/en/
tutorial.html. SERVO Magazine,
as a service to the building
community, is summarizing the
tutorial in a series of articles
beginning with part of Chapter 2,
“Design Fundamentals.” Look for
the rest of Chapter 2 and additional
chapters in the future. All
information here is provided
courtesy of Professor Meggiolaro
and RioBotz.
Scale Factor
One important thing to keep in
mind during the design phase is
the scale factor. If the physical
dimensions (length, weight, height)
of a bot are doubled, the volume
cubes. However, the cross sectional
area of a structural member just
doubles, so its strength doesn’t
keep up with the weight/volume.
What does this have to do with
combat robots? Everything.
If you want to take your 12
pound hobbyweight design and
scale it up to a 120 pound
middleweight, you’d need
to multiply the weight by
10. You’d do this by
multiplying all the
dimensions by the cube root
of 10, or 2.15. If you were
going to double a 60
pound bot’s weight,
you’d be building
a 120 pound
middleweight with a
scale factor of the cube root of two,
or 1.26, so all dimensions should be
increased by 26%.
Obviously, there is a lot more to
this. Volume doesn’t automatically
equal weight unless the density is
the same, which means precise
scaling of components. Using
commercial parts with standard
sizes, this won’t exactly happen.
Also, stress and strength aren’t
linear factors. The tutorial recommends raising the scaling factor to a
power of 1.5 in critical components
like weapon shafts to account for
TABLE 2
WEIGHT CLASS
• 60 pound Lightweight
• 120 pound Middleweight
• 220 pound Heavyweight
• 340 pound Super-Heavyweight
DIAMETER
0.5”
0.75”
1.0”
1.25”
Weight Classes
Combat robots
range in size from
the unnamed one
ounce miniatures,
through 50 or 75
gram fleaweights,
up to 390 pound
megaweights. Table
1 summarizes current weight classes.
Middleweight, Hobby-weight,
Beetleweight, and
Fleaweight versions of the
same “Touro” drumbot
design, stacked to illustrate
scaling factors.
TABLE 1
NAME
• Unnamed
• Fleaweights, Nanoweights,
UK Fairyweights
• US Fairyweights, UK Antweights
• US Antweight
• Beetleweight
• Kilobots
• Mantisweight
• Featherweight
(full combat & Sportsman)
• BotsIQ (small class)
• Hobbyweight
(full combat & Sportsman)
• Lightweight
• Middleweight
• Heavyweight
• Super-heavyweight
WEIGHT
1 ounce
50 or 75 grams
150 grams
1 pound
3 pounds
1 kilogram
6 pounds
12 pounds
15 pounds
30 pounds
• Megaweight
60 pounds
120 pounds
220 pounds
340 pounds (US);
320 pounds (UK)
390 pounds
SERVO 06.2009
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