Last year, we reported that MIT’s cheetah robot broke the speed record for four-legged robots by running at 18mph. Now, MIT researchers say that their robotic version of the wild cat may soon outpace its animal counterpart in running efficiency! The robot’s streamlined stride and its lightweight electric motors produce high torque with very little energy wasted.
Speaking about the development, MIT Department of Mechanical Engineering professor Sangbae Kim said that traditional robots had been held back by “heavy gasoline engines and hydraulic transmissions”. “In order to send a robot to find people or perform emergency tasks, like in the Fukushima disaster, you want it to be autonomous,” Kim says. “If it could run for more than two hours and search a large field, that would be useful. But one of the reasons why people think it’s impossible to make an electric robot that does this is because efficiencies have been pretty bad.”
With the Cheetah, MIT sought to create a robot with the perfect balance of flexible response upon impact, high power, torque and efficiency — characteristics that have historically been difficult to achieve with electric motors. The research team found that most wasted energy came from three sources: “heat given off by a motor; energy dissipated through mechanical transmission, such as losses to friction through multiple gear trains; and inefficient control, such as energy lost through a heavy-footed step, as opposed to a smoother and more gentle gait.”
To combat heat loss from motors, the group proposed a high-torque-density motor that produces increased torque relative to its weight and heat production. They found that high-torque motors also require fewer gears — a characteristic that would improve efficiency even more, as there would be less machinery through which energy could dissipate. The group installed shock absorbers to minimize shaking and stabilize the robot, and they found a way to capture lost energy and direct it back to the electric motors.
“The majority of impact energy goes back to the battery because the damping is created by custom-designed electric control of the motor,” Kim says. “[The motor] regenerates energy that would have been lost. There are so many ways to design, and each legged robot has a different system. If you design the motor properly, it’s more powerful, simpler robotics.”
Images: MIT (M. Scott Brauer)