Build Your Own Combat Robot

FIGURE 2-1
The welded frame
structure of Minion.
(courtesy of
Christian
Carlberg)
Chapter 2: Getting Started 25
Wheels are the most effective way of providing propulsion to a bot. They are
cheap, and easy to mount, control, and steer, and there are several methods you
can use. We’ll discuss all this in Chapter 3. There are many sources of bot wheels,
from toys for the smaller bots to small trailer tires for larger machines. Some
builders have used wheels from industrial casters, lawnmowers, go-karts, and
even small bicycles. Your choice depends on the size and steering configuration of
your bot’s design.
The majority of bots use differential or tank-type steering (also known as “skid
steering”). This means that the bot uses different speeds for left and right wheels (or
sets of wheels), causing the bot to go straight, or to one side or the other. Having one
wheel stopped and the other moving makes the bot pivot on the stopped wheel, and
vice versa. Having one wheel move forward and the other in reverse makes the bot
spin about its center axis. (We’ll discuss this in more detail in Chapter 3.)
Once you choose your locomotion method, the first set of major components
you need to identify are the motors. Most motors operate at speeds that are way too
fast to control the robot. So, you’ll need a gear reduction. Some motors have built-in
gearboxes, while others require a speed reduction system. This can be in the form of
gears, sprockets, belts, or even gearboxes. Chapter 6 will talk about these various
power transmission methods. The advantage of a gear reduction is an increase in
the torque to the wheels, which gives your bot more pushing power. Another reason
you should select your motors first is that they will dictate your electrical power
requirements, which affects the battery and motor speed controller selections.