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188 CHAPTER SEVEN
doses.” At the very least, that should prod the curious. As in all things, some truth can
be found in everyone’s thinking.
ENERGY REUSE, REVISITED
Although it is difficult to reuse energy by converting it from one form to another, it is
easy to reuse energy in its existing form. We’ve already seen how we can use the exist-
ing kinetic energy of the robot to coast to a destination and save energy. We can extend
this concept further by keeping track of the kinetic energy in various parts of the robot.
Here’s an example.
Suppose a robot has a relatively human form. This being the case, we can run a quick
experiment using on our own bodies. Stand up one arm’s length away from a light switch
on the wall with your left shoulder closest to the wall. Now turn so that your right shoul-
der is closest to the switch with your left shoulder away from it. If you want to turn on
the light switch with your left hand, you have a couple of ways to accomplish this task.
You can rotate right (90 degrees) at the waist until facing the wall and only then raise
your left arm to touch the switch. These two motions are disjointed and consume rela-
tively known quantities of energy.
An alternative way to do this is to raise your arm to touch the switch when the rota-
tion is halfway completed (45 degrees). It may seem easier to do it this way because the
momentum of the arm is already headed in the direction of the switch when the rota-
tion is halfway completed. But if the rotation of the waist is completed before the arm
is raised, energy is wasted in raising the arm.
The bottom line is that robots can use coordination. Very few people ever bother to
define just what human coordination is. All we know is that some athletes seems to soar
above the others effortlessly and perform dazzling feats. But broken down to physics,
at least some aspects of coordination come down to energy conservation and the con-
servation of momentum. Just as the human brain must act to turn a awkward person into
a graceful athlete, so too a robot’s control system must run algorithms capable of
streamlining the motions of the robot.
The motion and energy computations that would streamline the motions of the robot
need not be done at the spur of the moment just before they are needed. It is possible to
compute many of the motions ahead of time and store the results for future use. The
designers of the robot can experiment in advance to find the proper combinations of
motions to achieve a desired effect. If the robot’s repertoire of motions is small, this may
work well. But if the robot must move in multiple dimensions at once to achieve com-
plex, spur of the moment tasks, then the control system may need to perform these cal-
culations quickly, in real time.