Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Chapter 6 Steering History 197
Figure 6-8 Drive/steer module
with vertical compliance
All-terrain cycles (ATCs), when they were legal, ran power through a
differential to the two rear wheels, and steered with the front wheel in a
standard tricycle layout. ATCs clearly pointed out the big weakness of
this layout, the tendency to fall diagonally to one side of the front wheel
in a tight turn. Mobility was moderately good with a human driver, but
was not inherently so.
Quads are the answer to the stability problems of ATCs. Four wheels
make them much more stable, and many are produced with four wheel
drive, enhancing their mobility greatly although they cannot turn in
place. They are, of course, designed to be controlled by humans, who
can foresee obstacles and figure out how to maneuver around them. If a
mobility system in their size range is needed, they may be a good place
to start. They are mass-produced, their price is low, and they are a
mature product. Quads are manufactured by a number of companies
and are available in many size ranges offering many different mobility
capabilities.
As the number of wheels goes up, so does the variety of steering
methods. Most are based on variations of the types already mentioned,
but one is quite different. In Figure 4-30 (Chapter Four), the vehicle is
divided into 2 sections connected by a vertical axis joint. This layout is
common on large industrial front-end loaders and provides very good
steering ability even though it cannot turn in place. The layout also