Page 29 - Introduction to Autonomous Mobile Robots

Chapter 2
14
Type of motion Resistance to motion Basic kinematics of motion

Flow in
a Channel Hydrodynamic forces Eddies

Crawl Friction forces Longitudinal vibration

Sliding Friction forces Transverse vibration
Oscillatory
movement
of a multi-link
Running Loss of kinetic energy pendulum

Oscillatory
movement
of a multi-link
Jumping Loss of kinetic energy pendulum

Rolling of a
polygon
Walking Gravitational forces (see figure 2.2)

Figure 2.1
Locomotion mechanisms used in biological systems.

Owing to these limitations, mobile robots generally locomote either using wheeled
mechanisms, a well-known human technology for vehicles, or using a small number of
articulated legs, the simplest of the biological approaches to locomotion (see figure 2.2).
In general, legged locomotion requires higher degrees of freedom and therefore greater
mechanical complexity than wheeled locomotion. Wheels, in addition to being simple, are
extremely well suited to flat ground. As figure 2.3 depicts, on flat surfaces wheeled loco-
motion is one to two orders of magnitude more efficient than legged locomotion. The rail-
way is ideally engineered for wheeled locomotion because rolling friction is minimized on
a hard and flat steel surface. But as the surface becomes soft, wheeled locomotion accumu-
lates inefficiencies due to rolling friction whereas legged locomotion suffers much less
because it consists only of point contacts with the ground. This is demonstrated in figure
2.3 by the dramatic loss of efficiency in the case of a tire on soft ground.