Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

154 Chapter 4 Wheeled Vehicle Suspensions and Drivetrains
Figure 4-26
Rocker bogie
can negotiate obstacles that are twice the wheel height. This figure shows
only the basic parts of the mobility layout. The part labeled “chassis” is
the backbone or main support piece for the main body, which is not
shown.
The very fact that each wheel is passively loaded by the rocker bogie
suspension reduces its negotiable chasm width. Lockable pivots on the
bogie can extend the negotiable chasm width by making the center
wheels able to support the weight of the entire vehicle. This adds yet
another actuator to this already complicated layout. This actuator can be
a simple band or disc brake.
The rocker bogie suspension can be skid steered, but the side forces
on the wheels produce moments in the rockers for which the rockers
must be designed. Since the wheels are at the end of arms that move relative
to each other, the most common layout puts a motor in each wheel.
Steering is done by turning both the front and the rear wheels with their
own steering motors. This means that this layout uses 10 motors to
achieve its very high mobility. In this design, the large number of actuators
reduces the number of moving parts and over all complexity.
The steering geometry allows turning in place with no skidding at all.
This is the layout used on Sojourner, the robot that is now sitting on Mars
after completing an entirely successful exploration mission on the Red
Planet. Mobility experts claim this layout has the highest mobility possi-