Les Earnest

Stanford Cart

December 2012

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The Stanford Cart has had a 46 year career of ups and downs. It was born as a research platform for studying the problem of controlling a Moon rover from Earth. It then was reconfigured as a robot road vehicle for research in visual navigation, then went into show business for a few years. It now is on display in a home for retired robots at the Computer History Museum .

Stanford Cart with cable, 1961

1960-61 - The Stanford Cart was originally constructed by Mechanical Engineering (ME) graduate student James L. Adams to support his research on the problem of controlling a remote vehicle using video information. He had been working at the Jet Propulsion Laboratory on a NASA project called Project Prospector, which was proceeding with the assumption that someone on earth could drive around the Moon using a TV camera on a vehicle and a radio control link However Adams showed that assumption to be false.

The Cart had four small bicycle wheels with electric motors powered by a car battery and carried a television camera with a fixed view in the forward direction. Tests were conducted using both 2-wheel steering, like a car, and 4-wheel steering, in which the wheels and television camera swivel together. The cart was connected by a very long cable to a control console with a television display and controls for steering and speed. A magnetic tape loop made it possible to vary the time delay of steering commands, to simulate communication delays.

Adams explored the controllability of the vehicle while avoiding obstacles with various combinations of communication delay and speed. When steering commands are delayed by communications there is a tendency for the operator to over-steer and lose control. Among other things, Adams showed in his dissertation that with a communication delay corresponding to the round trip to the Moon (about 2 1/2 seconds) the vehicle could not be reliably controlled if traveling faster than about 0.2 mph (0.3 kph).

Stanford Cart with radio links, 1963

1962-63 - Mechanical Engineering graduate student Paul W. Braisted devised a scheme to improve the controllability of the vehicle by adding an analog computer that functioned as a predictor that took into account preceding steering commands and put a bright dot on the television screen at the predicted location of the cart when a current steering command would begin to take effect. With this addition the vehicle could be controlled at 5 mph (8 kph). Still there was a fundamental limitation on teleoperation in that if the travel during the time delay is greater than the distance from the vehicle to an unseen obstacle there is no way to avoid hitting it. Braisted completed his dissertation in 1963.

However, the immediate prospect of applying this technology was put off as a result of President John F. Kennedy's announcement on September 12, 1962 of the U.S. manned mission to the Moon.

Stanford Cart configured as an autonomous road vehicle at SAIL

1964-71 – The cart evidently sat unused in a Mechanical Engineering laboratory until 1966 when Les Earnest, who had recently joined the Stanford Artificial Intelligence Lab (SAIL) as Executive Officer, found it and talked its creator, James Adams, into letting SAIL use it to try making a robot road vehicle using visual guidance. However the radio links and other electronics that had existed earlier had vanished, so he recruited Electrical Engineering PhD student Rodney Schmidt to build a low power television transmitter and radio control link to undertake the visual guidance project.

SAIL was granted an experimental TV license by the Federal Communications Commission for Channels 22 and 23 and experimental operation began with a human operator controlling the cart via the computer based on television images. This initially allowed students to drive it around the neighborhood while seated at a desk watching television views, which became a popular pasttime. Prof. John McCarthy then became interested in the project at this time and, as Director of SAIL, took over its supervision. Using the KA10 processor, which ran at about 0.65 MIPS, Schmidt was eventually able to get the cart to automatically follow a high contrast white line under controlled lighting conditions at a speed of about 0.8 mph (1.3 kph), considerably slower than had been hoped for. Schmidt completed his dissertation in 1971.

Stanford Cart with slider, 1979

1971-80 - The cart was changed from 4-wheel to 2-wheel steering during this period. Hans Moravec, who had come to Stanford specifically to work on visual navigation, stayed with it but suffered a setback in October 1973 when the cart toppled off an exit ramp while under manual control and ended up with battery acid throughout its electronics.

Moravec was able to enlist the aid of roboticist Victor Scheinman in 1977 to build a “slider,” a mechanical swivel that moved the television camera from side to side allowing multiple views to be obtained without moving the cart. Using the KL10 processor then available, which ran at about 2.5 MIPS, Moravec was eventually able to use multi-ocular vision to navigate slowly around obstacles in a controlled environment. The cart moved in one meter spurts punctuated by ten to fifteen minute pauses for image processing and route planning. In 1979, the cart successfully crossed a chair-filled room without human intervention in about five hours. Moravec completed his dissertation in 1980 and there is a short video of the cart in action.

1980-2000 – After SAIL was shut down in 1980 the cart again went into storage until 1987 when, at the request of the Computer Museum in Boston, a number of retired robotic devices were sent to a new exhibit there. The Smart Machines Theater, later renamed Robot Theater, was a collection of artifacts on stage, lit up in sequence with some moving in their moments of glory, synched to a video, proving that even old robots can have a second career in show business.

Meanwhile in 1980, upon completion of his PhD, Hans Moravec moved to Carnegie Mellon University’s Robotics Institute which had been founded earlier by Prof. Raj Reddy, another SAIL graduate. In 2003 Sebastian Thrun moved from that organization to Stanford, revived SAIL and initiated a new autonomous vehicle project, as discussed below.

2000-present After the Boston museum shut down, the robots and other artifacts were sent to its successor, the Computer History Museum in Mountain View, California. Beginning in 2011 it was put on static display at the Museum, where it can be seen today. Perhaps some day it will again be allowed to roam the world.

Successors

More recently SAIL, under the direction of Sebastian Thrun, developed a robot vehicle called Stanley, which in 2005 won the DARPA Grand Challenge, a race across the Nevada desert. In 2007 the SAIL team took second in the DARPA Urban Challenge, which simulated an urban driving environment.

Sebastian Thrun and some of his colleagues then moved to nearby Google and created the Google driverless car which is still under development though Thrun has gone elsewhere.

Acknowledgement

Thanks to James Adams, Bruce Baumgart, Hans Moravec, Oliver Strimpel and Sebastian Thrun for providing information for this account.

References

The following Ph.D. dissertations at Stanford University came out of research with the Stanford Cart.

[1] Adams, James Lowell, Remote control with long transmission delays, PhD in Mechanical Engineering, 1961.

[2] Braisted, Paul Wilder, Study of a predictor for remote control systems operating with signal transmission delays, PhD in Mechanical Engineering, 1963.

[3] Schmidt, Rodney Albert, Jr., A study of the real-time control of a computer-driven vehicle, PhD in Elecetrical Engineering, 1971.

[4] Moravec, Hans Peter, Obstacle avoidance and navigation in the real world by a seeing robot rover, PhD in Computer Science, 1980.