An AI-designed quadrupedal robot developed by the Korea Advanced Institute of Science and Technology (KAIST) ran a whole marathon using just one charge, covering a distance of 42.195 kilometers within 4 hours, 19 minutes and 52 seconds.

The robot was nicknamed RAIBO2 and took part in the Sangju Dried Persimmon Marathon along with humans in November 2024. The research team led by KAIST mechanical engineering professor Je Min Hwangbo has now published its analysis of the robot’s energy efficiency in Nature.

The RAIBO2 managed an average speed of 2.64 meters per second in the competition and used up around 1,280 watt-hours of energy. The robot’s battery has a total capacity of 2,016 watt-hours. This means that there is much spare energy left for the robot after the race. From the leftover energy, the scientists believe the robot could drive for about 25 more kilometers.

The marathon’s course included about 286 meters of total elevation change, slopes approaching 18 degrees and sections of asphalt covered with fallen leaves.

The team used the event as a real-world test of the robot’s ability to maintain energy-efficient locomotion over a long distance.

The researchers focused on reducing energy losses throughout the robot rather than relying on a larger battery alone.

RAIBO2 uses lightweight legs, integrated motor-driver electronics and a high-torque-transparency joint mechanism. Its locomotion controller was trained with reinforcement learning, allowing the robot to adjust its movement to reduce losses when its feet contact the ground.

The system can also recover some mechanical energy while traveling downhill. KAIST said the robot’s joints allow energy generated during descent to be fed back into the system, partially offsetting the energy required to climb.

According to the Nature paper, RAIBO2 recorded a total cost of transport of about 0.25, compared with a human benchmark of 0.37. The researchers also report that the robot can travel more than three times as far per battery charge as existing quadrupedal robots considered in their comparison.

That comparison is based on energy-efficiency measurements and battery-range data from previous quadruped research, rather than a claim that RAIBO2 has been deployed for three times the operating range of every existing commercial robot.

The marathon itself took place nearly two years before the publication of the new research. KAIST originally reported the finish in November 2024, describing RAIBO2 as the first quadrupedal robot to complete a full marathon in an official event.

The work remains a research demonstration rather than evidence of a commercially deployed marathon-capable robot.

According to researchers, the increase in efficiency might assist in extending the range of operations of legged robots, which includes robots designed to operate outdoors where battery replacements may prove to be difficult. However, the current study does not establish a commercial product, customer deployment or production schedule.