Two-legged robot takes machines in a new direction
Engineers at the Institute for Human and Machine Cognition in Pensacola, Florida have developed a two-legged robot that uses mechanical design – rather than sensors – to maintain stability. The simple machine, called the Planar Elliptical Runner is driven by a single motor, and relies on the elliptical motion of its legs to stay upright. The engineers behind it wanted to examine how mechanical design could be used to create sophisticated legged locomotion, and suggested it could be used in niche areas such as nuclear power plant decommissioning and planetary exploration.
In contrast to many other legged robots, this one doesn’t use sensors and a computer to help balance itself. Instead, its mechanical design provides dynamic stability as it runs. “All the intelligence is in the physical design of the robot itself,” says Jerry Pratt, a senior research scientist at IHMC who leads the team that developed the robot. Pratt's group at IHMC is working on a range of different robots.

The design might feed into future systems. “We believe that the lessons learned from this robot can be applied to more practical running robots to make them more efficient and natural looking,” Pratt adds. “Running will be eventually useful for any application that you want to do quickly and where wheels can't work well.”

Pratt previously led a team that participated in the DARPA Robotics Challenge, a contest that saw robots try to perform a series of tasks in an environment designed to simulate a nuclear disaster. The challenge showcased some spectacular technology, but numerous mishaps and falls also highlighted the difficulties robots face dealing with unfamiliar, real-world situations. Many of the robots involved in that challenge used two legs, but some were unable to walk over sand or uneven ground (see “Why Robots and Humans Struggled with DARPA’s Challenge”).

The Planar Elliptical Runner has a single motor that drives the legs, and the elliptical motion of its legs together with its body shape provide inherent stability. The robot runs at 10 miles per hour, but if it were the size of a human it would travel at 20 to 30 miles an hour, the researchers say.

There is a small but growing interest in finding commercial uses for legged robots.

Boston Dynamics, a prominent robot maker owned by Alphabet, has shown two- and four-legged systems carrying boxes around warehouses and delivering packages outdoors. A company spun out of the University of Oregon by Jonathan Hurst, a professor of mechanical engineering, has developed another ostrich-inspired system called Cassie. Researchers at the University of Michigan led by Jessie Grizzle, a professor there, are developing advanced algorithms that allow for more efficient and graceful dynamic locomotion. Machines that balance themselves dynamically can traverse difficult terrain, but they are complex, expensive, and power-hungry.

“Robots with legs will be particularly useful in places where you want a human presence, but it's too dangerous, expensive, or remote to send a real human,” Pratt says. “Examples include nuclear power plant decommissioning and planetary exploration. These are very small, niche, markets, though.”