Like humans, robots that are working hard generate a lot of heat, a byproduct that adds stress to their systems and limits the amount of time they can be active before they need to recharge. One of the things that makes humans such good distance runners is our ability to sweat, a liquid discharge that helps to cool our bodies as it evaporates. Researchers at the University of Tokyo's JSK lab decided to borrow from that behavior to try and improve robotic performance, building a metal frame that could be filled with water which would seep out when it was in motion.
The team created custom "bones" by 3D printing porous aluminum. Water moves through these channels in predictable ways, and the "sweat glands" are positioned near motors, the pieces that typically overheat during strenuous activity. The unit can run for about 12 hours on half a cup of water, and the teams testing found that it was about three times more efficient with the sweat method than it was with ordinary air cooling.
The sweat method wasn't quite as effective as traditional active cooling, which involves a system of radiators, tubes, and fans. But it took up far less space, allowing the team to pack more sensors, circuits, and gears onto the robot. It's a promising avenue for further research, although there's no word yet on how scientists plan to deal with the robot's stinky armpits.