RAIBO2 robot dog runs full marathon faster than average in single battery charge

A four-legged robot built by researchers in South Korea has demonstrated it can complete a full marathon on one battery charge. The robot, called RAIBO2, ran the Sangju Marathon in South Korea alongside human competitors, finishing in 4 hours, 19 minutes and 52 seconds, a pace that beat the average human runner.

Built by a team at the Korea Advanced Institute of Science and Technology, RAIBO2 traveled roughly three times farther per charge than existing four-legged robots. Researchers say the achievement could point toward longer battery life for legged robots used in search and rescue.

Why legs cost energy

Legged robots hold real promise for disaster response and mountain rescue work, since they can cross terrain that wheels cannot. Until now, though, most quadruped robots have been limited to about 12 miles (20 kilometers) per charge.

Unlike wheeled machines, legged robots burn energy constantly just holding up their own weight, and each footstep wastes additional power. Roboticist Choongin Lee, the study’s lead author, said the team focused on cutting energy lost per unit of distance traveled rather than chasing speed alone.

Finding energy losses

The researchers found that about two-thirds of a legged robot’s energy budget disappears as heat inside its motors and drive electronics. The remainder is lost to gear friction, slipping feet and the jolt of each footfall.

To fix that, the team lightened each leg, designed lower-resistance motor circuit boards, and used the resulting weight savings to fit a bigger battery. They also built motors that produce the same torque using less current, and trained RAIBO2’s walking style through reinforcement learning that rewarded soft footfalls and penalized slipping or overheating. The robot was also designed to recover some energy on downhill stretches, feeding it back into the battery.

A new efficiency record

During the race, RAIBO2 held an average speed of 5.9 miles per hour (2.64 meters per second) across a course with 938 feet (286 meters) of elevation change and slick patches of terrain. It used 1,280 watt-hours of its 2,016 watt-hour battery capacity, achieving a total cost of transport, a standard measure of energy spent per unit of body weight and distance, of 0.25.

That figure beats the human benchmark of 0.37, making RAIBO2 the first quadruped robot on record to move more efficiently than an average human runner. Researchers estimate the robot could have covered another 16 miles (25 kilometers) before running out of charge, giving it a projected range of around 40 miles.

Sarah Bergbreiter, a mechanical engineer at Carnegie Mellon University who was not involved in the study, said she was impressed by the robot’s combination of efficiency, speed and mobility.

Still needs a human

The robot cannot yet navigate on its own. It carried a camera during the race but no software to interpret the road ahead, so a human operator steered it remotely throughout the course. Katie Byl, an engineer at the University of California, Santa Barbara, who also was not involved in the research, said RAIBO2 was essentially running blind.

Lee said adding autonomy would require additional onboard computing power, which costs energy. His team is now developing smaller onboard networks and sensors intended to add capability without a major increase in power use.