Machina Speculatrix
Over
fifty years ago W. Grey Walter started building three wheeled, turtle like,
mobile robotic vehicles. These vehicles had a light sensor, touch sensor,
propulsion motor, steering motor, and a two vacuum tube analog computer. Even
with this simple design, Grey demonstrated that his robots exhibited complex
behaviors. He called his creation Machina Speculatrix after their speculative
tendency to explore their environment. The Adam and Eve of his robots were
named Elmer and Elsie ( ELectro MEchanical Robots, Light Sensitive. ) The
following is a photo of Elsie without her shell.
The following is a
spectacular photograph taken by Eric Long of the second generation Grey Walter
turtle in the collection of the Smithsonian Institution. It is presented here
by permission from Peter Liebhold of the Smithsonian Institution.
His robots were unique
because, unlike the robotic creations that preceded them, they didn't have a
fixed behavior. The robots had reflexes which, when combined with their
environment, caused them to never exactly repeat the same actions twice. This
emergent life-like behavior was an early form of what we now call Artificial
Life.
In the 1950's Grey wrote
two Scientific American articles and a book "The Living Brain." You
can probably find them in a local library. There are several excellent online
articles about Grey Walter and his robot turtles that include photographs of
them searching for lights and avoiding obstacles. I have obtained
permission from Scientific American and the original illustrator Bernarda
Bryson to reproduce some of the illustrations from the 1950 article. The first
shows Grey's turtle (he called it a tortoise) seeking a light while the second
shows the reaction of the tortoise to a short obstacle.
I have started to
recreate the basic structure of the robots using LEGO
Mindstorms. Grey's turtles used a front wheel drive tricycle style chassis. The
propulsion motor sits in the fork of the front wheel assembly and moves with
it. The steering motor is mounted to the body and rotates the steering assembly
trough a worm gear. The light sensor is rigidly fixed to the steering assembly
so that it is always pointing in the direction of travel. This is my third
generation design and I have reduced the construction to the bare necessities
to make it easier to build.
Grey's turtles had a
steering assembly that rotated 360 degrees and in only one direction. This
requires slip rings to carry electricity to the drive motor and the light
sensor. Since there is no LEGO part like this, I added a switch to detect when
the steering assembly is pointed backwards. This condition is used to reverse
the steering motor direction creating a windshield wiper action. The post that
supports the light sensor also pushes the switch. The small wheel on the front
is used for debugging and to set the initial direction.
The propulsion motor is
mounted in the fork of the steering assembly. It drives the front wheel through
pulleys and a rubber band. This gears down the speed and also smoothes out the
motion. Because the zero power level of the RCX was still too fast for some of
the modes of operation I used an on-for-a-while off-for-a-while scheme to slow
the motor down.
The touch sensor of
Grey's turtles was a stick-in-ring switch connected to a plastic shell that
covered the entire robot making it look like a turtle. This produced an all
around touch sensitivity that is difficult to reproduce with Mindstorms. I was
forced to make a homebrew stick-in-ring sensor by mounting a 1/4" inside
diameter, 12-10 wire gauge, connector (Radio Shack #64-3120) on a short piece
of copper rod for the ring and wrapping a LEGO cross axle with copper foil for
the post. The Shell is made as illustrated with the help of some extra #5201
Angle Pieces.
The turtles had four
modes of operation: Search, Move, Dazzle and Touch. The first three modes are
determined by light level. Dark is search, moderate light is Move and bright
light is Dazzle. Touch causes an oscillation between Search and Dazzle. In
Search mode the steering motor is on full and the propulsion motor is on half
speed. In Move mode the steering motor is off and the propulsion motor is on
full speed. And in Dazzle mode the steering motor is on half and the propulsion
motor is on full speed.
At first the Dazzle mode
may seem superfluous, but it really helps to create unique behaviors. For one,
it prevents the moth drawn to the flame phenomenon. When there are two light
sources, the turtle is drawn first to one light and then the other rather than
being stuck between the two. When lights are attached to the turtles
themselves, they are attracted and then repelled from each other creating a
dance something like mating and territorial aggression. The following are
illustrations used by permission from Scientific American and the original
illustrator Bernarda Bryson from the 1950 Scientific American article showing
the Dazzle mode in action.
Here is an example run
with my Mindstorms turtle. I made it by attaching a white board marker to the
back and letting it record the path it took while it drove over a large sheet
of plastic. The path was then transferred to graph paper and scanned into an
image. I think the behavior is pretty close to the ones that Grey recorded with
time lapse photography. Examples of the Grey's turtle paths can be found on
many of the links listed below.
I programmed the
Mindstorms turtle using Visual Basic through the Spirit.OCX. After
initialization the program is broken down into four tasks:
So far this program
doesn't even reproduce all of the functions Grey managed to make with only two
vacuum tubes. As time allows, I plan to duplicate the Walter turtle behavior
more exactly. It is a real testament to W. Grey Walter's genius that 50 year
after his experiments a state-of-the-art product is sold that allows people to
essentially duplicate his work.
References:
Walter, W. Grey,
"The Living Brain," W. W. Norton,
Walter, W. Grey,
"An Imitation of Life," Scientific American, May 1950, p42-45.
Walter, W. Grey, "A
Machine that Learns," Scientific American, August 1951, p60-63.
Morris, Brian, "The
World of Robots," Multimedia Products, 1985, p23.
Long, Eric, American
Heritage of Invention & Technology, Vol. 14, Number 4, Spring, 1999, Back
Cover.
More biographical
information about Grey Walter can be found in Mark Ward’s book on Virtual
Organisms.
A great Biographical Sketch
of Grey Walter by Walter Freeman in PDF form.
Robot Builder has an
article on W. Grey Walter
and His Turtle Robots.
Near the bottom of this
page is the text of the Time Magazine
article from March 27, 1950, p. 74:
Holland, Owen E.,
"Grey Walter: The Pioneer of Real Artificial Life, Artificial Life V :
Proceedings of the Fifth International Workshop on the Synthesis and Simulation
of Living Systems , Christoper Langton Editor, MIT Press, Cambridge, 1997,
ISBN# 0-262-62111-8, p34-44.
Levy, Steven,
"Artificial Life" Vintage Books, 1992, p 282-284.
This type of robot is
similar to Braitenberg Vehicles.
Or BEAM Robots.
Web Links:
Here is where you can
buy LEGO Mindstorms online.
The following link is
from Owen E. Holland: http://www.ias.uwe.ac.uk/Robots/gwonline/gwonline.html
There is also a Grey Walter
Picture Archive.
New Scientist article: http://www.robotbooks.com/robot-critters.htm
John Purbrick has
written a simulation
of Grey Walter's turtle that can be downloaded.
More general robot
information can be found on the Robotbooks homepage.
Professor Antonio
D'Angelo at an
Other Grey Walter sites:
http://www.frc.ri.cmu.edu/~hpm/book98/fig.ch2/p018.html
http://en.wikipedia.org/wiki/Walter_Grey_Walter
My General LEGO
Mindstorms site:
http://www.plazaearth.com/usr/gasperi/lego.htm