Machina Speculatrix by Michael Gasperi


The name of the Robot is: Machina Speculatrix
My name is:Michael Gasperi
My email is gasperi@alynk.com
Here is the description:

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 turtles exhibited complex behaviors. He called
his turtles 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.)

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." that you can probably find in a local library.
There are also several excellent online articles about Grey Walter and his
robot turtles that include photographs of the turtles
searching for lights and avoiding obstacles. 

I have started to recreate the basic structure of the turtles 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.

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. Rather than make a
non-LEGO shell I opted for a different solution. I put a rotation sensor on
one of the rear wheels. It is programmed so that if the
robot has not moved very much for a period of time, it is considered to be
blocked and will execute the touch reflex.

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.

For more information and images please go to this page:
http://www.plazaearth.com/usr/gasperi/walter.htm


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