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to move and to handle objects. One is mechatronic engineering de- sign, which couples the mechanical principles of wheels, gears, and joints to electrical and electronic devices such as computer chips and servos.A servo is a type of actuator that animates artificial limbs. It is similar to an electric motor, with a shaft that can be rotated to any desired angle as set by an electrical signal.The units are powerful for their small size, and because they can be positioned just as desired, are good choices for versatile control of artificial body parts.The charac- teristic whine that always seems to accompany robotic movement in the movies is the sound of a servo being driven to a specific position.

Equally important, and generally more difficult to construct, are the bodily senses and cognitive abilities that enable the being to work out, for example, where and how its legs must be set to walk in a given direction, and then issue the necessary commands to its servos. Thats a complicated task.To make it even more demanding, the com- putation and the mechatronic response must occur quickly enough to allow the being to function in real time.

Depending on the bodily details,different levels of cognitive abili- ties are needed.As we will see below, wheeled robots, for instance, and robots that walk on four or six legs need less brainpower than those that walk on two legs.


Like a tricycle resting firmly on its three wheels, a wheeled being rolling on more than two wheels is inherently stable, and needs mini- mal cognitive capability to maintain its balance.Wheels offer a rela- tively simple mode of locomotion that is a good choice for robots when humanoid appearance is neither necessary nor desired. Never- theless, wheels are not right in all circumstances.They work well on smooth surfaces, but rough terrain or a profusion of obstaclessuch as occur in nature, at disaster sites, or in warfarecan defeat them. Under those conditions, continuous treads or tracks with cleats, like those on a bulldozer or military tank, serve better and still provide stable underpinning.

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