now turn to constructing the motors and wheels.
You’ll need the following:
• Two — Tamiya #70093 three-speed crank
axle gearbox motor kits
• One pair — Tamiya #70096 off-road tires
These items are widely available through
online retailers and some local hobby shops. See
the Sources box for a selected list of Web retailers
that carry these and other Tamiya parts. Assembly
instructions are provided with the motor
gearboxes and wheels. You will need a #0 Philips
screwdriver and small needle-nose pliers. A pair of
flush cutters — like the kind for snipping off the
ends of wires when constructing circuit boards —
is useful for separating the various plastic pieces.
The gearboxes can be constructed using one
of three speed ratios: 17:1, 58:1, and 204:1. For
Phase 1 of the BeginnerBot, select the 204:1 ratio.
This is the slowest speed and the easiest to
control. You can always disassemble the motor
gearboxes and remake them at a faster speed (the
17:1 ratio is not useful for robot locomotion). Be
sure to save all the extra parts in a reclosable
plastic baggie so you can change out the gearing
should you ever want to.
Each gearbox kit comes with a long hex-shaped drive shaft. You’ll need to cut the shaft to
length as shown in Figure 8. Do this before final
assembly of the gearbox. After each gearbox has
been built (but before you have inserted the small
DC motor into the gearbox), loosen the set screw
that holds the drive shaft in place. Adjust the
position of the shaft within the gearbox as shown
in Figure 8. You want about 1” of the shaft
protruding from the outside of the gearbox.
Retighten — but don’t over tighten! —the set screw
when the shaft is in the proper position.
(In order to access the set screw, you may need to
manually rotate the gearing to make the screw accessible.
Each motor comes with its own miniature hex wrench for
tightening the set screw. Be sure to save the wrench for
use later.) The wheels likewise come with their own
assembly instructions. When mounting the rubber tires,
orient the treads so the “V” pattern points to the same
direction. Remember that the wheels are opposite one
another, so the rubber tires need to be mounted on their
wheel rims in mirror image.
FIGURE 8. The
construction detail of
the drive motors and
how the wheels are
attached. Note you
need to cut the drive
shaft to length as
FIGURE 9. Notice where to mount the motors and other
parts on the BeginnerBot base.
Assembling the Base and
With the motors and wheels made, you can now
assemble the BeginnerBot base and control panel. Refer to
Figure 9 for where to mount the motors, skid, and cable
clamp to the BeginnerBot base. The Parts List calls for
mounting the motors using 4-40 x 7/16” pan or flat head
screws. The head of the screws are on the side of the
gearbox; the nuts are on the opposite side of the base.
FIGURE 10. The balance skid is constructed using a pan
head machine screw and two nuts. The head of the
screw points down.
SERVO 08.2011 49