A four-legged robot that can complete a marathon on a single battery charge has been demonstrated by a team from KAIST. The robot, which completed the Sangju Marathon in South Korea in 4 hours and 19 minutes alongside human runners, traveled three times as far per charge than existing robots and could pave the way for improved battery life in legged robots.

Legged robots have the potential to assist in rescue operations in mountainous or disaster-stricken areas. However, recent advances in quadruped robots have been limited by their ability to operate beyond approximately 20 kilometers (12 miles) because of limited battery life. Unlike robots on wheels, legged robots must continuously expend energy to support their body weight and compensate for energy lost with each ‘step,’ reducing the distance they can travel between charges.

In their article published in Nature, Jemin Hwangbo and colleagues present RAIBO2, a four-legged robot designed to reduce energy loss through both software and hardware. Its features include lightweight legs, optimized motor-driving circuits and movement rules reinforced by machine learning.

In the marathon, the robot maintained an average speed of 2.64 meters per second (5.9 miles per hour), navigating a notoriously difficult course with 286 meters (938 feet) of elevation change and slippery sections of terrain. Upon completion of the run, RAIBO2 had used 1,280 Watt-hours (Wh) of energy and achieved an average total cost of transport of 0.25 (a measure of the energy expended during motion, factoring in the weight of the robot).

The authors propose that this is the first quadruped robot to have a lower cost of transport than the human value of 0.37. Based on the robot’s total battery capacity of 2,016 Wh, the authors estimate that RAIBO2 could have traveled a further 25 kilometers (16 miles). The robot travels approximately three times as far per battery charge as existing quadruped robots.

The findings offer insights into improving the efficiency of legged robots, with the aim of extending their operational ranges and boosting their utility.

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Lisa Lock

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Robert Egan

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