on the three-speed crank axle
gearbox.)
• Tamiya #70145 narrow tire set. These
are 58 millimeters (about 2-1/4”) in
diameter, and securely attach to the
round 4 mm axle shaft of the worm
gearmotors. The wheels come in
pairs, so you need just one set.
• Tamiya #70144 ball caster. Use this
instead of the static skid to provide a
unidirectional caster. You can select
any of four heights; when used with
the above motors and wheels, pick
the 16 mm height option. Drill either
two or three holes for mounting the
caster; the placement of the holes is
somewhat critical as there is little
room for error. You get two ball
casters in the set, but you only need
one.
FIGURE 5. Alternative
Mini T-Bot, using upgraded
worm gearmotors, wheels,
and ball caster.
The worm gears use Mabuchi RE-260
motors which (when operated at six volts) consume about
3 amps of current if stalled. That’s too much even for an
L298, so if you go this route you’ll want to consider using
more robust H-bridge circuitry.
Programming the Mini T-Bot
With your Mini T-Bot constructed, you’ll want to watch
it scoot around the floor. Your options are virtually
unlimited, but for demonstration purposes, I’ll discuss some
simple Arduino code you can use to run your Mini T-Bot
through its paces.
A Menagerie of Found Parts
There are plenty of everyday objects you can use for robot building — all it takes is looking at them a bit differently.
Here are some examples to whet your appetite:
Plastic storage containers. Available in square, round,
and other shapes, these durable plastic boxes — available in
the housewares section of any department store — can be
used with or without their press-on lid. Containers are
available from small snack size to big shoeboxes.
Plastic fishing tackle box. Wheels are mounted to the
sides of the box; motors, batteries, and other critical
components are placed inside. The box can be popped open
to gain internal access.
Small “dorm-size” trashcans. Just large enough to hold a
Big Gulp, these trashcans have a convenient cylindrical shape
and removable top. Great for building miniature R2-D2 bots.
Computer mice. A discarded computer mouse makes a
great body for a micro-miniature robot. Almost all mice can be
disassembled by removing one or two screws on the bottom.
Take out the innards and install small motors, a small battery,
and a one-chip brain.
Compact discs and DVDs. Save the world’s landfills and
use these 4. 7” diameter discs for robot bases. Use care when
drilling holes in the plastic; the material can shatter into very
sharp pieces. If you need added strength, sandwich two discs
together.
Solderless breadboards. Solderless breadboards are
used to experiment with circuits before using more permanent
solder and wire-wrap construction. Mount motors and wheels
on the underside of your solderless breadboard, and you
create a versatile and ever-changeable mobile robot.
Plastic project boxes. These boxes — sold by RadioShack
and other electronics stores — are made to hold custom
electronics projects. The boxes come with removable metal or
plastic lids to allow access to the inside. The plastic is easily
drilled for mounting stuff.
Clear or colored display domes. Also called a hemisphere
or half-round dome, display domes can be purchased in sizes
from about 2” to over 12” in diameter. The dome can be used
as the body of the robot, or as a cover to protect its
electronics. A “robotic ball” can be made by gluing two domes
together.
PVC irrigation pipe. All forms of polygonal frames can be
constructed using PVC irrigation pipe. Most hardware and
plumber supply stores carry PVC pipe in various sizes and wall
thicknesses.
Hardwood laminated flooring samples. Already in about
the right size and shape for a small bot, these samples are
made by laminating a thin veneer over a sheet of high density
board. Thickness is about 1/4”. Cut off the tongue-and-groove
edges used to assemble the wood to make flooring. Round off
the corners to keep the wood from chipping.
SERVO 06.2011 45
