Submitted version of the thesis - Airlab, the Artificial Intelligence ...

2.1. Locomotion 11
Omnidirectional robots that are able to move in any direction (x, y, θ) at
any time are also holonomic. There are two possible omnidirectional configurations.
Thefirstomnidirectional wheel configuration has three omniwheels, each
actuated by one motor, and they are placed in an equilateral triangle as depicted
in Figure 2.7. This concept provides excellent maneuverability and is
simple in design, however, it is limited to flat surfaces and small loads, and
it is quite difficult to find round wheels with high friction coefficients. In
general, the ground clearance of robots with Swedish and spherical wheels
is somewhat limited due to the mechanical constraints of constructing omnidirectional
wheels.
Figure 2.7: Palm Pilot Robot with omniwheels
Thesecond omnidirectional wheel configuration has fouromniwheel each
driven by aseparate motor. By varyingthe direction of rotation and relative
speeds of the four wheels, the robot can be moved along any trajectory in
the plane and, even more impressively, can simultaneously spin around its
vertical axis. For example, when all four wheels spin ’forward’ the robot as
a whole moves in a straight line forward. However, when one diagonal pair
of wheels is spun in the same direction and the other diagonal pair is spun
in the opposite direction, the robot moves laterally. These omnidirectional
wheel arrangements are not minimal in terms of control motors. Even with
all the benefits, few holonomic robots have been used by researchers because
of the problems introduced by the complexity of the mechanical design and
controllability.
In mobile robotics the terms omnidirectional, holonomic and non holonomic
are often used, a discussion of their use will be helpful. Omnidirectional
simply means the ability to move in any direction. Because of the
planar nature of mobile robots, the operational space they occupy contains