resin and formed around the plug —
will take all of the original’s characteristics, including any scratches and
imperfections. Think about this effort
when deciding if you want to go with
a fiberglass shell.
Considering the cost of custom
molded fiberglass shells and the work
required, I would recommend two other
approaches. By far, the cheapest
approach is to use ready made items
like the cases of computer equipment,
office machines, industrial machines,
and even consumer appliances. You will
still require an internal skeleton to support
the shells and internal mechanisms.
Another design method is to build a
metal exoskeleton upon which you can
apply plastic or aluminum sheets.
The first method may leave your
robot looking a bit like an office
machine, but can still result in a quite
pleasing appearance. The second
method might result in a slightly
“boxy” appearance, but your robot will
be cheap and very sturdy.
angle extrusions are quite strong, easy
to drill, and great for all sizes of robot
structures. The 6061-T6 alloy is also
just about right for bending and it is
resistant to cracking.
The sheet aluminum plates are
also of 6061-T6 that I sheared with a
small metal shear, but can also be easily
cut with a saber saw or wood cutting
bandsaw fitted with a fine-toothed
metal blade. I have even cut very thick
aluminum stock for years with a 14”
bandsaw that was made for wood
working, but I highly recommend protecting the motor from the aluminum
dust that can be sucked into the motor
and cause it to go up in flames.
Notice that I used screws and nuts
to assemble the aluminum angle
extrusions to the plate stock pieces.
Yes, I could have used a MIG wire
welder and done a fair job of attaching
the pieces to each other, but I might
have ended up with a slightly warped
skeleton after the joints had cooled.
That happened to me one time and
“un-welding” a structure is almost
impossible; I had even used a jig fixture
to hold it square and it still warped
after I took it out of the fixture.
You’re in luck if you have access to
a heli-arc or TIG welding system, but
you should spend quite a few months
practicing before welding the final
parts. A good welder (and I’m not one
of those) can weld aluminum and create
a great structure, but there are several
negatives. It is very difficult to change
things and warping is very common
with amateur welders. The use of
screws allows you to disassemble and
change the design easily; they also
allow a tiny bit of “slop,” so the
structure is not as stiff — a good thing.
The Guts of the
I have never been a big fan of
plywood robots, even though my first
large robot was made entirely of
plywood and weighed a ton — well,
maybe 350 pounds. Plywood and
wood pieces may seem very easy to
drill and mount things upon; I have
seen some very nice robots made
almost exclusively of plywood structure.
Most projects, however, seem to take
on a “non-professional” appearance
after a period of design changes and
the resulting “trial” holes drilled in the
wood. The best tried and true method
seems to be the use of angle aluminum
pieces for the support edges of a sheet
aluminum exoskeleton shell.
Figure 2 shows the chest structure
of this large robot. This particular robot
used external fiberglass shell pieces to
cover the internal structure, so it didn’t
need to be completely covered with
aluminum, although you might do so
with your bot. The vertical structural
metal angle pieces are 1” x 1” x 1/16”
thick 6061-T6 aluminum. I have found
over the years that these aluminum
The best part of constructing a
robot is designing and building the
arms, mechanisms, and control systems.
For the dentist’s robot, a quick survey
of the human-sized machine told me
that it would weigh approximately 200
pounds. I had to look at all the structural
and mechanical systems of the robot
and scale them proportionally to this
particular robot design.
Weight and balance is important
in a large robot, as most are tall and
can tip over far more easily than
a squat, combat machine. Heavier
batteries, actuators, and motors are
kept as low as possible to bring the
center of gravity (CG) as close to the
floor as possible.
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