Obstacle Avoidance and Navigation in the Real World by a Seeing Robot Rover, Hans Moravec, 1980
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Appendix 2: History

The following chronology, which goes to 1974, was written in 1974 just before the meeting that resulted in the acquisition of the new cart TV transmitter and my first foray into cart vision. It provides a historical perspective on the history of Chapter 2. Many of the emotions expressed in it were fleeting.


A cart, thrown together by Mechanical Engineering for a short term research project, becomes available to the AI Lab. Les Earnest seizes on this as an opportunity to add mobility to the lab's bag of tricks, and convinces Rod Schmidt to do his thesis on the subject.


Schmidt spends several years single-handedly constructing radio links between the cart and the PDP 6. In this he values quick completion over high quality, and succeeds at least in minimizing the quality. It quickly becomes obvious that the model airplane control link (unlike the link used by M.E., presumably) is incapable of specifying the position of the four wheel steering (which has a range of two full turns) with manageable accuracy (a 5% jitter in the control pulse width is a 30° change in the wheel orientation). His solution is conversion of the steering to a conventional arrangement, which requires a much smaller total range of steering angles. Vic Scheinman helps, but his emphasis too is on speed over sturdiness. The first few attempts don't work very well, because simple connection of the front wheels with a chain drive causes them to want to go in slightly different directions when pointed anywhere but straight ahead. A bar linkage is finally installed. This doesn't work very well either, because of the short wheel base, but everyone is tired, and in any case there are no other new ideas. The result is a general mechanical degradation. Schmidt, now under the guidance of McCarthy, uses this vehicle to write a thesis concerning automatic cars. Realizing how long he has already been here, he applies to the thesis the same attitude that has made the hardware what it is, and completes it with the minimum possible expenditure of effort. He is aware of the state of things, and includes in it (on p 151) the paragraph:

“In conclusion let me comment that this vehicle was intended as a low-budget way of getting some experience with driving problems, and that if this research is continued, a new vehicle should be obtained. The lmitations on operating time caused by battery discharge and the lack of equipment space, nonexistent suspension, and low speed of the present vehicle will make future work increasingly difficult and unrealistic.”

The silence is deafening.


Baumgart decides he likes the idea of a robot that reasons visually, and concocts a grand scheme in which every scene viewed by the camera would be related to a model of the lab and surrounding territory. He notices the uncertainty in the analog link, and decides make it into a digital one. This is his first digital design effort, and the result, which provides for on-off control of the motors and has no indication of the orientation of anything, is considerably inferior to the original in concept, and in addition works unreliably. The original servo electronics are disassembled or misplaced, making his changes irreversible. He rationalizes that the problems with the link are unimportant, since, when his visual reasoner works, it will be able to deduce the state of things, and detect when a transmitted command has failed, to try again. The enormity of the effort needed to make his plan a reality becomes apparent to him as he works on sub-problems. Since it would become possible to actually use a vehicle only when his proposed scheme was almost completed, and since he now sees that it is unrealistic to think that it could be brought to fruition in a reasonable number of years, he abandons any serious efforts directly concerned with the cart, but maintains his association with it, as a status symbol and a toy. He occasionally drives it around for show, often over rough ground, contributing to its mechanical decline. During this time several other graduate students are steered towards this essentially nonexistent “cart project”. They are disillusioned by the lack of a coherent plan and suffer from too little guidance and from conflicts with Baumgart's personality. All these associations are short lived and unhappy. Baumgart finds success and happiness working on the graphics and vision sub-problems suggested by his original concept.


Quam, having done his thesis on the processing of Mars pictures, expresses an interest in using the cart for Mars rover research. He has picture processing algorithms, but little else. Interfacing with Baumgart is impractical, so nothing much happens. Moravec, who had decided he liked the idea of an automatic car before he came here, and who had wanted to come to Stanford largely because of that, decides it is time to start serious work towards a thesis on this topic. He is steered towards Quam, who, at this stage, has little to offer other than admonishions to “get this show on the road”. He trys, rebuilds the control link to make it a little more reasonable, and plays with the vehicle for a few weeks, contributing to further deterioration in its already delicate mechanical condition. Then, in collaboration with Quam, who is tuning up his picture correlation programs, he writes a control package for vehicle. Before these two efforts can be combined, he throws a wrench into the works by running the cart off a ramp, which provides the excuse to stop working that the TV transmitter had been looking for from the day it was born. He spends six months trying to recover from the effects of his folly, with only limited success. Very frustrated and anxious to get back to productive work, he writes a proposal to McCarthy and Earnest, begging for help out of his predicament. For similar reasons, on a slightly larger scale, Quam writes a proposal to his friends at JPL.

The story to this point was an example of that well known conservation law “you can't get something for nothing”. By definition, there can hardly be a cart project without a cart, since in the absence of a vehicle we have only computer vision. The impression grows on me that what we have now is worse than no vehicle at all. At no time has the state of the cart hardware ever approached a level comparable to that of the hand-eye in the Rancho arm days, yet the comparison between the two projects is undoubtedly behind the hostility the cart now faces. I wonder if any arm theses would have gotten beyond the first few months if the arm required massive repairs after every half hour of operation, and if these repairs had to be effected by the student trying to write the programs. This situation is exactly the one that has faced everyone considering doing a cart thesis. It instantly excludes those who are not hardware inclined, and makes technicians of those who are.

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