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A new step forward for robots

Engineers decode human balance to build walking robots.

By Jesse EmspakCorrespondent for The Christian Science Monitor / December 8, 2009

Jerry Pratt (l.) with research associates push M2V2 to test its balance at the Institute for Human Cognition in Pensacola, Fla.

Carmen K. Sisson/Special to The Christian Science Monitor


For the past 30 years, scientists and technicians have grappled with making robots walk on two legs. Humans do it effortlessly, but the simple act has a lot of hidden complexity. And until recently, computers were very bad at it.

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Now, several teams across the country are refining the first generation of robots that are close to walking like people. That includes the ability to recover from stumbles, resist shoves, and navigate rough terrain.

In walks PETMAN, designed by Boston Dynamics in Waltham, Mass. The two-legged robot saunters with uncanny realism. The android has no upper body, just steel and plastic legs attached to a system of power cables. But it walks on its own, using the same heel-to-toe motion that humans use. When pushed from the side, PETMAN sidesteps to recover its balance. The robot even wears shoes.

Why make a robot like this? Researchers say walking robots provide them with a benchmark to gauge engineering precision, a chance to improve the lives of older people, and the ability to create more useful machines capable of navigating a world built for humans.

In PETMAN’s case, the Army, which funds the project, needs a machine that can simulate realistic human motions to test dangerous equipment such as chemical protection gear. Boston Dynamics plans to deliver a version with a head and a torso by early 2011.

Marc Raibert, founder and president of Boston Dynamics, says the secrets of balance were almost a complete mystery back in 1980, when he and other robotics experts started the Leg Lab at Carnegie Mellon University in Pittsburgh. In 1986 he moved the Leg Lab to the Massachusetts Institute of Technology in Cambridge, Mass.

With “a lot of the first walking robots, [scientists] tried to make them like a table,” he says. Researchers thought that robots should be permanently stable. These early efforts in robotics attempted to program exactly where each foot should fall, calculate all the possibilities ahead of time – but human and other animals don’t work that way. Instead, we are actually in a kind of controlled fall, using our feet to sense how best to regain balance after each step.

So, the students at the Leg Lab tried different tacks. They created a succession of robots ranging from stiff-legged machines that bounced to droids that looked progressively more natural. Boston Dynamics’ first successes jogged on four legs, such as Big Dog, a military project designed to carry heavy loads across rough terrain. Big Dog can negotiate snow, forests, and rocky hills – terrain that might stymie wheeled vehicles.

Until recently, moving over anything but level ground was out of the question for most robots. Perhaps the most famous walking humanoid robot, ASIMO, was introduced as a prototype by Japanese car company Honda in the early 1990s. Even after years of revisions and learning to run, ASIMO can still be pushed over easily, struggles with uneven terrain, and moves with a bent-knee gait that doesn’t look much like normal walking.

Leg Lab alumni have since fanned out to several different universities and corporations. One of them, Jerry Pratt, is a research scientist at the Institute for Human and Machine Cognition in Pensacola, Fla.