W. Grey Walter and his Turtle Robots

by Arthur Ed LeBouthillier

This article appeared in the May 1999 issue of "The Robot Builder"


Simple robots based on animal-like neural systems and behaviors may seem like a novelty today, but they have their genesis in the work of one of the early pioneers of robotics and artificial life, W. Grey Walter. W. Grey Walter developed a number of robots in the 1940’s and 1950’s which demonstrated great sophistication for their day. The technique he used are reflected in today’s reactive and biologically-inspired robots such as those based on the B.E.A.M philosophy.



Born in Kansas City, Missouri in 1910, William Grey Walter later moved to England where he got his education and started a career as a neurophysiologist. As part of this endeavor, he studied the operation of the brain in-depth through the instrument which he had developed into a practical tool, the Electroencephalogram (EEG). In using this instruments, H. Grey Walter was responsible for identifying the brain waves known as Alpha, Delta and Theta waves.


Walter’s Robots

In order to better understand the operation of animal brains, Mr. Walter  proposed building simple models of their basic operations. In 1948 and 1949, Mr. Walter built two robots to demonstrate his theories of nervous systems. Named Elmer and Elsie (short for ELectro MEchanical Robots, Light Sensitive), Walter’s robots were simple front wheel drive tricycle-like robots covered by a clear plastic shell. These first robots were rather crude prototypes but his technician later built better quality robots on his design which were widely shown in public. These robots represented some of the first examples of autonomous robots.


Machine Speculatrix

Mr. Walter dubbed his first type of robot “Machina Speculatrix,” because "it explores its environment actively, persistently, systematically as most animals do". The first robots each used one vacuum tube to simulate two interconnected neurons. These simple amplifier circuits connected two sensors to two motors. The first sensor was a photocell and it was connected to the drive and steering motors. The second sensor was a contact switch that indicated that the turtle’s “shell” had bumped into something; this sent the vacuum-tube amplifiers into oscillation and changed the robot’s direction. This circuitry allowed the turtles to wander a room and return to a hutch to recharge their batteries.

From the simple neural circuitry, several sophisticated behaviors arose. Under normal operation, the steering motor turned slowly with the drive motor at half speed. This scanned the photocell and produced an arcing motion. When the photocell detected a bright-enough light, the turning stopped and the robot headed towards it. This demonstrated simple phototropic (light attracted) behavior. Once the light detected by the photocell became too bright, though, the steering motor began turning; this demonstrated photophobic (light avoiding) behavior. If the shell struck an object, then the system would oscillate until it successfully avoided the object.

Machina Docilis

After building his first robots, Mr. Walter added additional capabilities naming his new robot, Machina Docilis. Based on the same physical design, these robots included a Conditioned Reflex Analogue (CORA) which demonstrated simple Pavlovian learning. The new robots had three sensors: a sound detector, the light detector and a bump switch. The CORA circuitry could be trained to establish learned connections between the three sensors and the motor drive oscillators. This resulted in an ability to learn different behaviors which were initiated by sounds, light or the bumpers. This kind of circuitry is structurally very similar to neural circuitry most recently identified in marine snails.

Roboticist’s Inspiration

W. Grey Walter’s work has inspired generations of roboticists. Rodney Brooks, recent innovator of reactive robots, drew on Walter's work. As a child, Brooks had read Walter's book, The Living Brain, and built his own versions of the machines described in it. Even this author has to credit seeing pictures of Walter’s robots as being a major motivator for his interest into robotics.


W. Grey Walter was a robotics pioneer who demonstrated early autonomous robots based on neural-like circuit designs. His robots demonstrated sophisticated emergent behaviors despite their very simple construction. His designs were responsible for motivating generations of robotics enthusiasts.