Section of Final Report: NASA ACRP NCC7-7, Bush Robots, Hans Moravec, Jesse Easudes


1: Motivation

Most present day remote controlled and robot arms fall short of human dexterity, especially in their viselike hands, which are unable to manipulate complicated objects, or apply the combinations of forces needed to accomplish some simple tasks. These limitations, among others, exclude them from many interesting applications in construction, repair and exploration.

Some research manipulators achieve better dexterity by imitating the structure of the human hand, often at the expense of precision, strength, reliability and especially economy. Robot hands with three, four and five dexterous fingers have demonstrated the ability to roll eggs, twirl batons and tie knots.

There are imaginable tasks (for instance, those requiring simultaneously maneuvering together more than three uncooperative components in a precise way) for which even human dexterity is inadequate. Today, most are never attempted, while a few are approximated using specialized tools and fixtures.

Finer Fingers

It may be possible in future to leapfrog the dexterity not only of conventional mechanical manipulators, but of human hands. Consider the following observation.

Once upon a time, the most complex animal was a worm. The stick-like shape was poorly adapted for manipulation and even locomotion. Then these stick-like animals grew smaller sticks, called legs, and locomotion was much improved, although they were still poor at manipulating. Then the smaller sticks grew yet smaller sticks, and hands, with manipulating fingers were invented and precise manipulation of the environment became possible.

Generalize the concept. Visualize a robot that looks like a tree, with a big stem, repeatedly branching into thinner, shorter and more numerous twigs, finally ending up in vast numbers of microscopic cilia. Each intermediate branch would have several degrees of freedom of sensed and controlled motion. Though each branch would be a rigid mechanical object, the overall structure would have an organic flexibility because of the huge numbers of degrees of freedom. At the outer extremes, the machine would have an enormous number of individually positionable and naturally swift manipulators, coordinated for simultaneous execution of otherwise unimaginable tasks by signals and power from the central regions.

Taken far enough, the smallest fingers operate at nanoscale, able to shape matter at the atomic level. Compared to the free-floating, self-powered, self-directed nanobots envisioned by others, each nano finger in a bush robot would be a simple device, controlled, coordinated and powered by mechanically connected computers and energy sources located in the direction of its stem. Bush robots may provide a uniform, top down, incremental bridge to nanotechnology. Macroscopic machines with a few levels of branching could be built today, and could exhibit human-like dexterity. As microtechnology advances, the number of branching levels could be increased with ever finer sub-fingers. An ultimate nanoscale bush robot might begin with a stem a meter in length and a few centimeters in diameter, able to move with a one second timescale. At 30 levels of branching, one might find a billion fingers each a micron long, able to move at a megahertz. At 50 levels, there could be 1015 fingers, each a nanometer long, and in principle able to move at gigahertz rates, if not constrained by exotic physical effects.