Build Your Own Combat Robot

FIGURE 14-3
Wheel shown
bolted to
drive plate.
Chapter 14: Real-Life Robots: Lessons from Veteran Builders 311
The ammo box was destined to receive all the electronics. It took time to determine
the arrangement of all the items inside the limited space. Inside the ammo case
are the Vantec speed controller, the radio and its battery pack, two Futaba servos
driving standard microswitches to switch the weapons systems, and three relays for
the weapons systems—two for the arm mechanism and one for the saw motors. An
evening of careful planning and trial-and-error assembly found the configuration
that worked best. They all fit, albeit in a densely packed configuration.
Between the axle and the rear of the box are the batteries—two high-rate-discharge
Yuasa MPH1-12 batteries that can supply 100 amps or more. They were
chosen for their high discharge rate, something many gel cell batteries are incapable
of, as it was needed to run the saw motors. Quality varies widely among gel cell
manufacturers. The Yuasas ran $26 each—not inexpensive, but battery quality is
an area where you can’t afford to scrimp. Everything was fitted in and tested; the
robot was driven around as a mechanical ammo box to be certain the design
worked. The axle through the center of the robot, the gearbox, and the wheels
help to brace the batteries in place. The motors are held in place by hose clamps
over PVC pipe. It may not have looked pretty, but the parts were inexpensive, effective,
and easily obtainable. Most of this robot’s parts were obtained from scrap
yards, hardware stores, scavenged materials, and a surplus catalog or two. Although
work on the basic drive box was completed and initial testing showed the
design to be a solid one, there was still much more work to be done.
Step 4: Creating Weapons and Armor
Chew Toy’s weapon is a rotary spinning mass. The design is simple: two milling
saws on each side of the prow are driven by a chain sprocket mechanism. As you
can see in Figure 14-1, a large chain sprocket was used; it takes chain reduction