STEAM may be the answer to a problem that has always dogged robotics: how to feed a robot enough energy to do useful work.
A team at Vanderbilt University in Tennessee has tackled the problem by using hydrogen peroxide to generate steam. This powers novel robot motors that pack 50 times the punch of the best electric motors of similar size and weight.
A major barrier holding back humanoid robots is the lack of decent motors. They also need a power supply that doesn’t take all the robot’s available energy just to lug it around, says Michael Goldfarb at the university’s Nashville campus.
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So while Honda’s acclaimed P3 humanoid robot looks impressive as it walks around and climbs stairs, its batteries are so heavy that it only has enough power for 15 to 25 minutes, and even then it doesn’t have enough strength to do much useful work. Goldfarb reckons that a similar robot equipped with his new steam-powered motor would be a lot faster and could operate for up to 10 hours.
The Vanderbilt motors harness energy liberated when liquid hydrogen peroxide (H2O2) decomposes to form oxygen and water. The reaction, set off by a palladium catalyst, is almost instantaneous, and the heat it generates turns the water into high-pressure steam. This is fed into a chamber where it forces a piston to expand. Controlling the steam with a system of springs and valves allows the piston to extend and retract as required, says Goldfarb.
Electric motors trade power for speed: you can get one or the other but not both. Vanderbilt’s steam pistons give you both, says Jerry Pratt at MIT’s robotic locomotion centre, the Leg Lab. “There’s also a good power-to-weight ratio,” he adds.
Other researchers have tried using small hydrocarbon combustion engines to drive compressors or hydraulic pumps for robots or future “exoskeleton” suits for soldiers, (91av, 10 November 2001, p 32). But these devices are noisy and polluting, and so can’t be used indoors, says Pratt.
But Goldfarb says the steam system is much more efficient at converting chemical energy to kinetic form, and doesn’t require the complex fuel mixing or ignition a combustion engine needs. And the only noise comes from the occasional hiss of spent steam being expelled.