Page 31 - Introduction to Autonomous Mobile Robots

16

Figure 2.4 Chapter 2
RoboTrac, a hybrid wheel-leg vehicle for rough terrain [130].

In effect, the efficiency of wheeled locomotion depends greatly on environmental qual-
ities, particularly the flatness and hardness of the ground, while the efficiency of legged
locomotion depends on the leg mass and body mass, both of which the robot must support
at various points in a legged gait.
It is understandable therefore that nature favors legged locomotion, since locomotion
systems in nature must operate on rough and unstructured terrain. For example, in the case
of insects in a forest the vertical variation in ground height is often an order of magnitude
greater than the total height of the insect. By the same token, the human environment fre-
quently consists of engineered, smooth surfaces, both indoors and outdoors. Therefore, it
is also understandable that virtually all industrial applications of mobile robotics utilize
some form of wheeled locomotion. Recently, for more natural outdoor environments, there
has been some progress toward hybrid and legged industrial robots such as the forestry
robot shown in figure 2.4.
In the section 2.1.1, we present general considerations that concern all forms of mobile
robot locomotion. Following this, in sections 2.2 and 2.3, we present overviews of legged
locomotion and wheeled locomotion techniques for mobile robots.

2.1.1 Key issues for locomotion
Locomotion is the complement of manipulation. In manipulation, the robot arm is fixed but
moves objects in the workspace by imparting force to them. In locomotion, the environ-
ment is fixed and the robot moves by imparting force to the environment. In both cases, the
scientific basis is the study of actuators that generate interaction forces, and mechanisms