Homayoon Kazerooni is about to lift 500 pounds with one arm. The slender 36-year-old mechanical engineering professor is no bodybuilder, yet when he slips into an extender, he becomes a man of steel.
An oversize multijointed robotic arm, the extender is the brawniest of a half-dozen machines built by Kazerooni and a dedicated cadre of students at the University of California at Berkeley. All black metal, chunky, and menacing, it is hinged to a support pedestal like an abandoned prop from an Arnold Schwarzenegger movie. Motors bulge at every joint, and thick cables snake away to a nearby hydraulic engine the size of a desk.
Shoulder to shoulder with the extender, Kazerooni slides his right hand into a glove inside the machine’s hollow metal brace of a forearm, which extends a foot and a half beyond Kazerooni’s hand. At the end of the brace is the machine’s hand, two six-inch-square metal plates that open and shut like giant tweezers. Kazerooni’s left hand squeezes a hand-held safety switch, and the engine roars to life, drowning the lab in white noise. Kazerooni’s eyebrows cock, and a knowing smile breaks under his mustache. He begins to twist and bend his right arm, swiveling shoulder, elbow, and wrist like a tai chi master. Even though the pedestal- supported extender weighs 250 pounds, it moves fluidly and weightlessly along with Kazerooni’s arm. Then, when Kazerooni closes his right hand, the extender grabs a quarter-ton steel ingot and waves it triumphantly.
Welcome to the latest episode in the herky-jerky history of human amplifiers, machines designed to augment muscle power. Half gadgets, half garments, human amplifiers are the ultimate hard-guy hardware. But while they’ve long been a fixture in science fiction, they have yet to pull their weight in the real world. Engineers have been doggedly plugging away at them for more than 30 years, but they are technically complex. The results have been a series of elephantine contraptions and outlandish concepts. Kazerooni has inherited this dubious legacy and is bent on winning the human amplifier some newfound respect.
