Page 359 - Concise Encyclopedia of Robotics

One axle turns
at different speeds
Two-section robot Rear wheels run Work Envelope

Wheel-drive locomotion

the sections can be turned, causing the robot to change direction. This
scheme is shown in the lower illustration.
Simple wheel drive has limitations.One problem is that the surface must
be fairly smooth. Otherwise the robot might get stuck or tip over. This
problem can be overcome to some extent by using track-drive locomotion
or tri-star wheel locomotion. Another problem occurs when the robot must
go from one floor to another in a building. If elevators or ramps are not
available, a wheel-driven robot is confined to one floor. However, specially
built tri-star systems can enable a wheel-driven robot to climb stairs.
Another alternative to wheel drive is to provide a robot with legs.
This is more expensive and is more difficult to engineer than any wheel-
driven scheme.
See also BIPED ROBOT, INSECT ROBOT, QUADRUPED ROBOT, ROBOT LEG, TRACK-DRIVE LOCO-
MOTION, and TRI-STAR WHEEL LOCOMOTION.
WORK ENVELOPE
The work envelope is the range of motion over which a robot arm can move.
In practice, it is the set of points in space that the end effector can reach.
The size and shape of the work envelope depends on the coordinate
geometry of the robot arm, and also on the number of degrees of freedom.
Some work envelopes are flat, confined almost entirely to one horizontal

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