Humanoid robots place near-constant, high-torque demands on their motors and generate enough heat that it regularly impedes their performance. This problem is usually solved in mechanical systems by using fans, heat sinks, and radiators, which take up space and add mass. University of Tokyo researchers have designed “Kengoro” - a musculoskeletal humanoid with over 100 motors, and are using the robot’s skeletal structure (its metal frame) as a coolant-delivery system. Their technique goes beyond circulating water through the frame - they have allowed the water to seep out through the frame around the motors to cool them evaporatively. The frame is laser-sintered from aluminum powder. This technique is precise enough to build up aluminum structures with areas of both low and high permeability, allowing for seamless metal components that have microchannels embedded in them through which water can flow. The sweat “glands” that let water seep through the frame are positioned next to the robot’s motors. As the motors heat up during operation, the evaporating water efficiently cools them down.