A six-legged robot walks with no central control
In February 1989 Rodney Brooks described in MIT AI Lab memo 1091 a six-legged machine about 35 cm long and roughly 1 kg in mass, controlled by a network of 57 augmented finite state machines built incrementally: each network is a strict augmentation of the previous one, and at every step the robot remains a working system. The robot walks over rough terrain and follows a person it senses passively with six pyroelectric infrared sensors. The paper appeared in Neural Computation, volume 1, issue 2, in June 1989.
Why it matters
The subsumption architecture of 1986 had been a proposal; here is a robot that walks on it. Walking emerges from simple leg reflexes with no central control, which the author explicitly holds against the hypothesis from insect-walking studies that a central generator is needed. It is the idea that the world is its own best model, put into legs.
By figure 2 of the memo: each leg is rigid, attached at a shoulder joint with two degrees of rotational freedom and driven by two orthogonally mounted model-airplane servo motors (twelve in all, which is this record's arithmetic rather than a figure in the text); an error signal tapped from the servo circuitry gives a crude force measurement (5 bits including sign) on each axis; the other sensors are two front whiskers, two four-bit inclinometers (pitch and roll) and six IR sensors with about 6 degrees of angular resolution over a 45 degree span; four on-board 8-bit microprocessors on a 62.5 Kbaud token ring, about 1 Kbyte of RAM and 10 Kbytes of EPROM, three silver-zinc batteries between the legs. All clocks in the network tick at about 0.04 s; messages are limited to 8 bits; inhibition and suppression last two ticks. The network can be run partially by deactivating later machines: the simplest level is standing up with two machines per leg, then a simple walk, and so on. The memo was read from the copy on the author's site (a scan without a text layer, pages 1 to 6 rendered); the DSpace download sits behind a human-verification step, which was not worked around. What the record does not claim: the name Genghis, which does not occur on the pages read and is used in the atlas as the common name of this machine; the walking speed and the battery life.