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44 Modern Robotics

Robot Mules

An important early advance in many civilizations was the use of
beasts of burden such as horses, mules, oxen, and camels to carry
goods. In the past few years, Raibert has been a key researcher in
a project to create the mechanical equivalent of the mule. Called
“BigDog,” a prototype walking robot offers the military the
ability to increase the carrying capacity of infantry. The robot

SOLVING PROBLEMS: ROBOTS AND ANIMATION

In 1872, photographer Eadweard Muybridge (1830–1904) set up a
series of cameras at a racetrack. Each camera was set up so that as a
galloping horse passed, a cord would break and a picture would be
taken. The result was the first photographic study that revealed the
exact sequence in which the legs of the horse moved. If one takes
enough such pictures in rapid succession the result is a “moving pic-
ture”—a movie.
While film can be used to “decompose” walking or running into
discrete movements, traditional animation is the reverse process. It
attempts to create smooth action from a series of discrete images.
There have been many approaches to animation, ranging from car-
toons with hand-painted frames (cels) to computer animation that uses
algorithms to create smooth transitions from one defined “key frame”
to the next.
The ultimate problem for animators is how to turn discrete images
into smooth, realistic motion. One approach commonly used is to cap-
ture the motions of live human actors and incorporate them into the
animation model. Unfortunately, the ability to integrate such captured
motion smoothly is limited—fundamentally, because the modeler lacks
real understanding of the mechanics and dynamics. Without knowing
why things move the way they do, the ability to determine where they
should move next is limited.
One of Raibert’s key insights is that the same algorithms that
enabled his robots to walk or run smoothly and realistically could also