Researchers from the University of Tokyo have solved a cooling problem on their humanoid robot by learning from biology: this robot sweats.

Kengoro is a musculoskeletal bot, designed to work as much like the human body as possible and to study how the robotic body interacts with the environment. The IEEE profiled it in a recent article. In order to make it work, the researchers have had to balance weight and efficiency: the humanoid form was a good idea in terms of keeping the robot’s weight down, but it still calls for 108 individual motors and weighs 56 kilograms (123.5 pounds).

Adding radiators and fans to cool it would have made the robot too bulky. Instead, the designers turned its metal skeleton into a network of carefully constructed channels. Water can flow through them and naturally evaporate, giving the robot the same cooling benefit as sweating gives humans – as long as the robot is topped up with water now and then.

The frame is made of laser-sintered aluminum, which can be built up with layers of high or low permeability. This lets water flow through the tiny channels in the aluminum. The different levels of permeability also prevent the water from simply spilling out of the robot; it seeps from a less porous layer to a more porous one, letting the water evaporate slowly.

In a recent test, this technique allowed the robot to run for half a day under moderate conditions on just a cup of water. It still isn’t as effective as using a radiator, but it is more effective than air cooling or simply piping the water around the body, and means that the robot’s frame weighs about the same as it would have if it was used only for carrying weight. Sometimes, the best designs are found in nature.