Andy Ruina: Simulating life with robotic efficiency, one step at a time

Andy Ruina, professor of theoretical and applied mechanics, in his Kimball Hall lab with one of the 19th-century children's walking toys that inspired his work on energy-efficient walking robots. Ruina discussed his work on the robots at a Feb. 17 news briefing at the AAAS annual meeting. Kevin Stearns/University Photography

By Bill Steele

Robots that walk like human beings are common in science fiction, but not so easy to make in real life. The most famous current example, the Honda Asimo, moves smoothly but on large, flat feet. And compared with a person, it consumes much more energy.

But researchers at Cornell, the Massachusetts Institute of Technology (MIT) and Holland's Delft University of Technology have built robots that seem to more closely mimic the human gait, and the Cornell robot matches human efficiency. The researchers' inspiration: simple walking toys that fascinated children in the 19th century.

"Already our robot seems to be at least 10 times more efficient than anybody else's," said Andy Ruina, Cornell professor of theoretical and applied mechanics, who discussed the robots at a news briefing at the American Association for the Advancement of Science in Washington, D.C., on Feb. 17. Ruina and his colleagues were questioned by a large press contingent, and Ruina gave interviews to newspapers and TV crews from the United States, Canada, Britain and Australia.

The Cornell robot consumes an amount of energy per unit weight and distance comparable to a human walker. In contrast, they estimate that the Honda Asimo uses at least 10 times as much energy as a human. The MIT and Delft robots, though not built deliberately to be energy-efficient, also use much less energy than the Asimo. More important, the researchers say, is that their robots provide a more realistic model of how humans walk.

Ruina, his former student Steven Collins (now a graduate student at the University of Michigan), MIT postdoctoral researcher Russ Tedrake and Delft postdoctoral researcher Martijn Wisse describe their new robots in the latest issue of the journal Science (Feb. 18, 2005).

Cornell's robot equals human efficiency, Ruina explained, because it uses energy only to push off, while other robots needlessly use energy to absorb work, for example in moving the limbs forward more slowly than they would naturally swing under gravity power. "In other robots the motors are fighting themselves," he said.

Researchers at each of the three universities have built walking robots, differing slightly but based on the same principle. They are an extension of several years of research into "passive-dynamic walkers" that walk down a shallow slope, very much like simple walking toys that have been around since the 1800s and developed more scientifically starting in 1988. These downhill walkers were developed further in Ruina's lab, leading to a two-legged version with articulated knees built by Wisse during a visit to Cornell. Collins further refined that and then built the first Cornell powered model, while Wisse returned to Delft and developed other unpowered and powered robots.

For the robots described in Science -- and on view at the AAAS -- the researchers at all three institutions have simply substituted small motors for gravity power. Ruina says the research followed the example of the Wright brothers, who carefully researched gliders, then simply added a motor to achieve powered flight.

The robot work was done primarily to study the biomechanics of human locomotion, but it could have applications in practical robotics. Collins noted at the press briefing that he is applying some of what he has learned to the design of a powered prosthetic foot for amputees. Information gained from studying walking robots should be of use to the rehabilitation community, he added.

The work in Ruina's lab was funded primarily by a National Science Foundation biomechanics grant.