66T, made of 14 gauge galvanized steel. The T
measures 6” x 5” with a strap width of 1-1/2”. The
66T — like most strapping Ts — already has holes in
it for nailing. The holes are offset and most will
not line up with hardware you want to hang on
your robot, so you’ll need to drill new holes. A
power drill (or better yet, a drill press) is
recommended for drilling the holes.
Constructing the
Mini T-Bot
The Mini T-Bot requires a few extra parts in
addition to the strapping T and assorted fastening
hardware. You are, of course, free to substitute
these for others you may have on hand or like
better.
You need two each of the following:
• Tamiya three-speed crank axle gearbox
motor, #70093.
FIGURE 2. The constructed Mini T-Bot,
with a pair of Tamiya three-speed crank
axle gearbox motors, small wheels
pulled from a dollar store toy, and a
non-rotating skid.
The Tamiya parts can be purchased from most any
online hobby retailer; see Sources for a selected list. The
motors are mounted on the ends of the crossbar. To keep
the cost of construction to a bare minimum, I’ve used a
non-rotating skid for balancing the other end of the robot.
The skid is nothing more than a 6-32 x 1/2” machine screw,
hex nut, and steel or nylon acorn (cap) nut. The roundness
of the acorn nut provides a smooth gliding surface.
For your reference, the finished Mini T-Bot is shown in
Figure 2.
Begin by assembling the two gear motors according to
their included instructions. With the Tamiya three-speed
crank axle gearbox, you can select any of three gear ratios:
17:1, 58:1, and 204:1. The 204:1 ratio makes for a fairly
slow bot, but it offers the most power for trekking through
dense carpet. Try the 58:1 speed, which should be
acceptable as long as the robot isn’t unnecessarily weighed
down. You can always disassemble the motors and change
the gear ratio.
After building the gearboxes, don’t snap in the motors
just yet. Use the included tube of grease to lubricate the
gears. Be sure to wash your hands to remove any grease
residue before continuing with the rest of the construction.
For my prototype, I used a pair of 1-1/2” diameter
(1/4” tread width) wheels I pulled off a toy purchased at
the nearby dollar store. The bore in the hub of the wheel
was already just the right diameter for the 3 mm hex axle
used with the gearbox motors. If your wheels have a small
bore, carefully drill it out to the proper size. Don’t make it
too large, or else the axle will simply spin inside the wheel.
Cut the axle to about 2-3/8” in length. Use a small
hammer to gently tap the axle into the bore of the wheel.
Then, secure the axle inside the motor using the included
setscrew. Use your fingers to manually rotate the gears so
that the setscrew is accessible from the top of the motor
(the bottom has the two flange eyelets for mounting).
Here are selected sources for the Tamiya motors, wheels, and
ball caster detailed for the Mini T-Bot, plus online sellers of
motor bridge modules:
Parallax - www.parallax.com
Motor bridge modules.
Sources
Pololu - www.pololu.com
Tamiya motors, wheels, and other accessories; selection of
motor bridge modules; high efficiency replacements for FA-130
motors.
Robotshop - www.robotshop.com
Tamiya motors, wheels, and other accessories; DFRobot
Arduino motor bridge; other motor bridge modules.
Robot Store/Jameco - www.robotstore.com
Selection of Tamiya motors and wheels; L298 motor bridge
chip; and assorted components.
Solarbotics - www.solarbotics.com
Tamiya motors, wheels, and accessories; motor bridge modules;
high efficiency replacements for FA-130 motors.
SparkFun - www.sparkfun.com
Motor bridge modules; breakout boards; and chip-level
controllers.
The Robot Marketplace - www.robotmarketplace.com
Tamiya motors, wheels, and other accessories; motor
controllers.
Tower Hobbies - www.towerhobbies.com
Full line of Tamiya products.
SERVO 06.2011 43
