Build Your Own Combat Robot

310 Build Your Own Combat Robot
Metal shops can also use your balsa template as a guide. If a shop is also going
to be doing all your welding, it is a good idea to give these folks your design sketch
and review it with them so they understand exactly what you want your finished
piece to look like. Showing them the balsa mockup before you disassemble it for
template parts is also useful, especially if you are working with people who have
no prior experience with robotics.
Step 3: Building the Bot
I decided to use a surplus ammo box as part of Chew Toy’s structure because it
was inexpensive, yet an effective way to house the electronics, but it wound up becoming
the structural backbone of the robot. All the weapons systems and other
features on Chew Toy are attached to the ammo box. The metal of the ammo box
was not as tough as I’d originally hoped, but it provided adequate protection from
impacts. All the electronics of the robot went inside, as well as the stationary axle
that was a part of the robot’s drive train. The axle—a long steel rod that goes
lengthwise through the center of the ammo box—does double duty as part of the
drive mechanism and as a means of holding the batteries securely in place.
The robot’s motive power is supplied by a pair of kiddy-car motors (power
wheel motors) that were inexpensive. I found them in the same surplus catalog
where I found the ammo box. Because of their low price, I could purchase extra
motors to use for experiments. When I tested these motors to achieve maximum
performance, I found that when these 12-volt units are run at 24 volts, a good
amount of power was produced. Subjecting motors to higher-than-rated voltage
occurs frequently at robotic competitions. It’s risky, though, so it requires a lot of
trial-and-error testing to determine how much extra voltage the motors can handle.
Chew Toy’s motors were broken in before being tested to their voltage limits.
It is also important to cool the motors properly. Breaking in the motors and
cooling them well will prevent their melting. I learned this the hard way during the
test phase. Knowing a few motors would fail during testing, we purchased extras
to ensure an adequate supply.
My team chose motors that were easy to modify and that were designed to use a
stationary axle. Working from the outside in, we attached the motor casing solidly
to the chassis. The armature of the motor is mounted on a hollow shaft, or torque
tube, that turns on the motor’s stationary axle. Attached to this torque tube is a plate
that transmits the motor’s power to the gearbox input. The motors use a threegear
reduction system that gives a motor-to-wheel ratio of 110 to 1, greatly increasing
the torque delivered to the drive wheels—no chains or belts here! The
wheels are also designed to fit on a stationary axle and have bearings so all that was
needed was to drill holes through the wheels and the drive plate of the gearbox and
bolt them together. If you look at how a wheel is arranged on the axle (Figure 14-3),
you can see a washer over the axle with a cotter pin securing the wheel in place.
The point where the wheel is bolted to the drive plate of the gearbox is also visible.
The wheels are decent sized with deep treads for added traction.