Page 66 - Build Your Own Combat Robot

Chapter 3:
Robot Locomotion
at your friend’s shop and he tells you that he’ll have to grind the rubber down, 47
rather than machine it like metal. After a few hours of experimentation, he hands
you two rubber drive spindles.
Now you have four spindles to mount both belts for a complete robot base, two
rubber and two aluminum. After assembly, you find that the new drive spindles
work pretty well. The rough ground surface of the spindle does a decent job of
gripping the smooth rubber belt’s surface. After trying the base out on the floor,
you find that the turning is erratic and decide that you need a row of idler wheels
to keep the entire length of each belt firmly on the floor. Your friend patiently ma-
chines for you 10 idler wheels, which you mount to a series of spring-loaded lever
arms. Wow, this robot is beginning to be a bit complicated! After a few tries on
your garage floor, you begin to notice that the teeth are wearing down. You smile
at your creation and decide to put it away. It was a good learning experience.

W heels: A Tried and True Method of Locomotion

Many people in the field of experimental robots would not think of any way to
make their robot move other than using tank-type treads. Others feel the same way
about legs, whether two, four, or six. As mentioned earlier, many other means of lo-
comotion and propulsion for robots are out there, including flying or swimming,
but we’ll concentrate on wheels from this point on. Wheels are pretty much proven
in all types of robot applications, from the smallest desktop Sumo machine to the
largest mobile industrial robots. Even designers for NASA’s Mars-exploration ro-
bots gave up on legs and other means of locomotion in favor of wheels.

Types of Steering
Wheels are generally categorized by steering method and mounting technique.
The two types of steering that are used with wheels are Ackerman steering and dif-
ferential steering.

Ackerman Steering

Ackerman steering, also known as car-type steering, is familiar to all of us. Figure 3-3
illustrates several variations of Ackerman steering. Note that only a single motor
source drives the wheels, and a separate motor controls the steering. This method
uses two wheels in the front turning together to accomplish the turn. Sometimes a
single wheel is used, as in some golf carts, or the rear wheels can turn, as in fork-
lifts. A child pedaling a tricycle is powering the front wheel, but she is also using
that same front wheel to control the direction of movement of the vehicle. This
turning method has been used in robot applications, but it is not as popular as the
differential drive method that we’ll discuss in a moment.