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welding (as is typical for assembling a
metal robot) since screws can be
removed or placed differently to
‘tweak’ a robot’s chassis — welds
cannot.
Aluminum sheet metal —
especially 6061-T6 stock — is, in my
opinion, the best material for a robot
base, though I have also used harder
7075 in applications where little
machining is required. Both types are
readily available at many locations and
are easy to cut with a bandsaw,
though I would suggest using a large
metal shear at a nearby machine shop
or technical college as the edges are
so much smoother (especially for
thicker stock). Small holes are easily
cut into thinner aluminum and steel
stock using a chassis punch as shown
in Figure 5. Drill a small pilot hole
and use a ratchet wrench to tighten
the three punch pieces until the
hole pops through.
Cutting large holes in any sheet
metal is a bit harder. Large bandsaws
have a way to cut the blade and insert
it in a small pilot hole, and then weld
it back together with a welder
mounted on the saw. If you don’t
have access to one of these, you can
use a Sawzall type of reciprocating
saw or hand jigsaw fitted with a metal
cutting blade to enlarge holes for
wheels and such.
It takes a bit of practice to cut a
nice hole. You’ll need to do a bit of
filing to smooth out the ragged
edges. A fly cutter as shown in
Figure 6 can cut larger round holes
using a drill press.
Make sure your work piece is
securely clamped down. Either of
these methods work for mild sheet
steel, as well. Plywood, HDPE, most
plastics, brass stock, and just plain
lumber can also be used for robot
bases and structure.
Designing Robots for
Outdoor Operation
Considering the growing
popularity of the RoboMagellan
contests around the country, I will
start with base designs that are best
for these types of autonomous robots
that must traverse rough outdoor
courses during competitions.
I was just at the SRS’s 2013
Robothon exposition at the Seattle
Center (in Seattle) and witnessed
off-road configuration RC
car chassis like Mark Curry’s
robot in the 2012 SRS
RoboMagellan competition
shown in Figure 7 is typical
of most entrants. Large
knobby tires coupled with a
beefy drive train mounted
on a rigid base can easily
traverse thick grass and
inclines.
A large hobby shop —
especially one that deals
mostly in off-road RC cars
Remember, it is not going to be
an RC vehicle anymore; you are going
to need special power supply setups
for the motor drivers and also for the
other electronics. Sensors (cameras
and object detection), GPS antenna
mounting, shaft encoders, and one or
more microcontrollers need unique
mounting locations.
If you are mostly interested in
RoboMagellan-style robots that
generally operate at lower speeds,
large shock-absorber mounted wheels
are not that important, but that also
depends on the area where the
competitions are to be held.
At this year’s Robothon, one
RoboMagellan contestant’s entry was
doing quite nicely until it happened
upon a steep 6” edge of grass next to
a sidewalk. Instead of smoothly
transitioning from the grass to the
pavement, the robot dropped at a 45º
angle to the edge of the concrete and
stalled, unable to move forward or
backward.
Look for vehicles that have wheels
that protrude past the front and rear
portions of the chassis to allow them
to grip and climb over obstacles.
Remember that larger wheels may
have more traction surface, but
Figure 7. Mark Curry's Nomad
in 2012 SRS RoboMagellan.
Figure 6A and 6B.
Fly cutter. Figure 5. Chassis punch in use.