A slight man with a stubbly gray beard and elfin features, Brown led me down a set of creaky stairs to his basement workshop. A smorgasbord of screws, wires and electronic capacitors filled rows of washed-out peanut butter jars that Brown had somehow affixed to the ceiling. In the world of robotics, one of his colleagues told me, Brown has a reputation as a “mechanical designer extraordinaire.”
“This is the graveyard,” Brown said, nodding at piles of wooden dowels, fiberglass strips and slotted aluminum shafts—detritus from the decade he’s spent refining his pogo stick, the BowGo. Razor, the company that rode the toy scooter to riches in the early 2000s, licensed Brown’s technology in 2010 and sells a children’s version of his stick, which they call the BoGo.
Brown developed the BowGo to prove a simple idea: that with the right design and materials, a lightweight spring could conserve an extraordinarily high share of the energy put into it, with minimal losses to friction.
“A pogo looks to us like a toy,” said Matt Mason, the director of Carnegie Mellon’s Robotics Institute, where Brown has worked for three decades. “To Ben, it’s an idea taken to its most radical extreme.”
Brown, a onetime mechanical engineer for Pittsburgh’s steel mills, joined Carnegie Mellon in the early 1980s and worked on Defense Department-funded research into “legged locomotion”—robots that walk, run and hop. The military was interested in vehicles that balanced on legs and could roam mountainsides, swamps and other terrain too rugged for trucks or tanks.
Brown and his colleagues built a stable of hopping one-legged robots that could leap over objects and move nimbly at nearly five miles per hour without losing their balance. But the hoppers—picture a 38-pound bird cage on a swiveling stilt—were energy hogs. Powered by hydraulics and compressed air, they had to be tethered to pumps, electrical outlets and computers. Brown was left wondering: Could you build a leg light and efficient enough to bounce without external power?
“Kangaroos were always inspiring,” Brown told me, “because the kangaroo uses an Achilles tendon that stores a huge amount of energy and allows it to hop efficiently.”
In the late 1990s he and a graduate student, Garth Zeglin, bent a six-inch length of piano wire and joined the ends with a piece of string that held the wire taut, like a bow. They called it a “bow leg,” and tested it on an inclined air-hockey table. When dropped, the leg flexed and recoiled, bouncing back to between 80 and 90 percent of its original height, a feat of energy conservation.
Brown wanted to put his idea to a bigger test. One route would be to build a battery-powered, human-size hopping robot with an onboard computer, stabilizing gyroscope and giant bow leg. He opted instead for a pogo stick.
“It was really the easiest way to build a robot without all the robot technology,” Brown said. The only power source, thrust actuator, leg position controller and altitude sensor you needed was a flesh-and-blood rider.