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Energy Recycling, Lighter Robo Legs

Humans are able to naturally recycle about 40% of the energy in a springy step. If this can be accomplished in artificial legs, then the motors and batteries will not have to be quite as large and heavy, making life easier for developers and potential future users of the technologies, such as exoskeletons, prosthetic limbs, robots and other artificial substrate locomotion devices.


Legs with joints driven by motors struggle to recycle energy during walking in the way biological legs with springy tendons and muscles do.This is essentially becuse usually motors are unable to recycle external forces acting upon them semi-randomly, and add that force to their own power, dialing down and up their own output.

However, thanks to scientists at Oregon State and Carnegie Mellon Universities, a new design of motorised leg, driven by steel cable tendons and with built-in springs could provide the answer.

"The spring is important. That's something that is fundamental to being able to run in an efficient way," says Jonathan Hurst, a roboticist at Oregon State University, Oregon. Hurst created three of the robot legs while a student at Carnegie Mellon University in Pittsburgh. One of them, called Thumper, joined him for his new appointment at Oregon State and is attached to a boom that prevents it from falling left or right, but not to the front or back

Two others, teamed up to to build a biped called MABEL, are at the lab of Hurst's collaborator, Jessy Grizzle, at the University of Michigan in Ann Arbor. The springs inside each leg can store a kilojoule of energy per kilogram, enough that a 75-gram spring can easily store the energy required for a single hop. To get the required power from a motor alone would require a motor that weighed 30 times as much as the spring.


New robot legs have a spring in their step

Grizzle's MABEL photos and video

IEEE Robotics and Automation Magazine

ECD Leg page

Lighter Robo Legs Thanks to Energy Recycling

Student Designs Robot Leg

Carnegie Mellon's Robotics Club

Jonathan W Hurst Contact Details

Staff Comments


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