GREY WALTER - The Cybernetic Brain - page 43

by a proliferation of such models, including the maze-learning robots built
by Claude Shannon and R. A. Wallace—which Walter liked to call Machina
labyrinthea —and Ashby's homeostat ( Machina sopora ) (Walter 1953, 122-23),
but we need to focus on the tortoise. 10
The tortoises (or “turtles”) were small electromechanical robots, which
Walter also referred to as members of a new inorganic species, Machina
speculatrix . He built the first two, named Elsie and Elmer, at home in his spare
time between Easter of 1948 and Christmas of 1949. In 1951, a technician at
the Burden, W. J. Warren—known as Bunny, of course—built six more, to
a higher engineering standard (Holland 1996, 2003). The tortoises had two
back wheels and one front (fig. 3.3). A battery-powered electric motor drove
the front wheel, causing the tortoise to move forward; another motor caused
the front forks to rotate on their axis, so the basic state of the tortoise was a
kind of cycloidal wandering. If the tortoise hit an obstacle, a contact switch on
the body would set the machine into a back and forth oscillation which would
usually be enough to get it back into the open. Mounted on the front fork was
a photocell. When this detected a source of illumination, the rotation of the
front fork would be cut off, so the machine would head toward the light. Above
a certain intensity of illumination, however, the rotation of the forks would
normally be switched back on, so the life of the tortoise was one of perpetual
wanderings up to and away from lights (fig. 3.4). When their batteries were
low, however, the tortoises would not lose interest in light sources; instead,
they would enter their illuminated hutches and recharge themselves.
The tortoises also executed more complex forms of behavior which derived
from the fact that each carried a running light that came on when the tortoise
was in search mode and went off when it locked onto a light. The running
lights were originally intended simply to signal that a given tortoise was work-
ing properly, but they bestowed upon the tortoise an interesting sensitivity to
its own kind. It turned out, for example, that a tortoise passing a mirror would
be attracted to the reflection of its own light, which light would then be extin-
guished as the tortoise locked onto its image; the light would then reappear as
the scanning rotation of the front wheel set back in, attracting the tortoise's
attention again, and so on (fig. 3.5). The tortoise would thus execute a kind of
mirror dance, “flickering, twittering and jigging,” in front of the mirror, “like
a clumsy Narcissus.” Likewise, two tortoises encountering one another would
repetitively lock onto and then lose interest in one another, executing a mat-
ing dance (fig. 3.6) in which “the machines cannot escape from one another;
but nor can they ever consummate their 'desire' ” (Walter 1953, 128, 129).