'Cheetah' Robot Hits High Speeds, Wastes Little Heat

A 70-pound “cheetah” robot designed by MIT researchers may soon outpace its animal counterparts in running efficiency: In treadmill tests, the researchers have found that the robot — about the size and weight of an actual cheetah — wastes very little energy as it trots continuously for up to an hour and a half at 5 mph. The key to the robot’s streamlined stride: lightweight electric motors, set into its shoulders, that produce high torque with very little heat wasted.

The motors can be programmed to quickly adjust the robot’s leg stiffness and damping ratio — or cushioning — in response to outside forces such as a push, or a change in terrain.

To combat heat loss from motors, the group proposed a high-torque-density motor — a motor that produces a significant amount of torque at a given weight and heat production. The team analyzed the relationship between motor size and torque, and designed custom motors that exceed the torque performance of commercially available electric motors. The team found that such high-torque motors require fewer gears — a characteristic that would improve efficiency even more, as there would be less machinery through which energy could dissipate.

The researchers also attached strips of Kevlar to connect sections of the robot’s legs, simulating the structure of tendons along a bone. The Kevlar strengthens the leg with little additional weight, and further reduces the leg’s inertia. The group also constructed a flexible spine out of rings of polyurethane rubber, sandwiched between vertebra-like segments. Kim hypothesizes that the spine moves along with the rear legs, and can store elastic energy while galloping.

Currently the team is assembling a set of new motors, designed by Jeffrey Lang, a professor of electrical engineering at MIT. Kim expects that once the group outfits the robot with improved motors, the cheetah robot will be able to gallop at speeds of up to 35 mph, with an efficiency that rivals even fliers. The researchers are convinced that this approach can exceed biological muscle in many aspects, including power, torque and responsiveness.