Page 335 - Robot Builder's Bonanza

304 BUILD ROBOTS WITH WHEELS AND TRACKS

using only one caster instead of two, or place slightly more weight over the end with the
caster. You may also reduce the height of the casters, or mount the casters on a spring
suspension, as shown in Figure 26- 4. Select a spring that, under normal load, just begins
to compress from the weight of the robot.

Two- Motor BasicBot

The BasicBot is a simple differentially steered base that’s easy to construct of wood, plastic,
cardboard, picture mat, or foamboard. It’s an ideal first robot, and its round shape makes it
well suited for use as a wall follower, maze solver, or other robot that works in confined spaces.
The base measures 5″ in diameter; many craft and hobby stores sell 1/8″- or 1/4″-thick wood
and plastic already cut into this size (or close to it), saving you from cutting out a circle using
a saw or mat- cutting blade. A finished BasicBot is shown in Figure 26- 5.
The BasicBot uses the following motors and mechanical parts, all of which are available at
Tower Hobby and many other online hobby stores (see Appendix B for Web sites).
• Tamiya Twin- Motor Gearbox, #70097. The motor comes as a kit and is assembled in
about 20 minutes using a screwdriver and small needle- nose pliers.
• Tamiya Ball Caster, #70144. You get two ball caster units; you need only one for the BasicBot,
so save the second caster for another project. Construction takes about five minutes.
• Tamiya Truck Tire Set, #70101. You get four tires; you need only two.

Tamiya also offers the model #70168 Double Gearbox kit. It is functionally identical to the
G Twin- Motor kit, except its dimensions are slightly different. This means that if you use the double
gearbox you’ll need to adjust the drilling pattern in order to properly mount the motor to your
robot base.

CONSTRUCTING THE BASICBOT
Refer to Figure 26- 6 for the cutting and drilling layout. Use a 1/8″ bit to drill the holes. The
location of the four holes on the base isn’t supercritical, but the spacing is. You may wish to
use the constructed motor and ball caster to mark off the holes.

1. Begin by constructing the twin- motor gearbox according to the instructions that come
with it. You have the choice of building the motors with a 58:1 or 203:1 gear ratio.
Opt for the 58:1 ratio if you’d like a faster robot. For maze following and other tasks
you’re better off with the slower, 203:1 ratio.
2. Before inserting the motors into the gearbox, solder wires to them and connect the
wires to a set of switches or control electronics. See Chapter 22, “Using DC Motors,”
for ways to control small motors.
3. Construct the ball caster according to the instructions that come with it. The caster
comes with various pieces to alter its height. Your finished caster should measure about
1″ from the base to the ball socket.
4. Mount the motor box and ball caster. Assuming a 1/4″-thick base, use 4- 40 1/2″
machine screws and nuts. You can use 3/8″-long screws if the base is 1/8″ thick.
5. Mount rubber tires onto two of the truck tires, then insert the wheels over the motor
shaft. Figure 26- 7 shows the underside of the BasicBot, with motor and ball caster
attached.

26-chapter-26.indd 304 4/21/11 11:52 AM