Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Chapter 4 Wheeled Vehicle Suspensions and Drivetrains 141
FOUR-WHEELED LAYOUTS
The most basic four-wheeled vehicle actually doesn’t even use a differential.
It has two wheels on each side that are coupled together and is
steered just like differential steered tricycles. Since the wheels are in line
on each side and do not turn when a corner is commanded, they slide as
the vehicle turns. This sliding action gives this steering method its
name—Skid Steer. Notice that this layout does not use differentials, even
though it is also called differential steering.
Skid steered vehicles are a robust, simple design with good mobility,
in spite of the inefficiency of the sliding wheels. Because the wheels
don’t turn, it is easy to attach them to the chassis, and they don’t take up
the space required to turn. There are many industrial off-road skid
steered vehicles in use, popularly called Bobcats. Figure 4-10 shows that
a skid steered vehicle is indeed very simple.
The problem with skid steered, non-suspended drivetrains is that as the
vehicle goes over bumps, one wheel necessarily comes off the ground.
This problem doesn’t exist in two or three wheeled vehicles, but is a
major thing to deal with on vehicles with more than three wheels. Though
not a requirement for good mobility, it is better to use some mechanism
that keeps all the wheels on the ground. There are many ways to accomplish
this, starting with a design that splits the chassis in two.
Figure 4-10
steered
All four fixed, skid