Humans get hot when they work out, and so do robots. Just as our muscles generate heat when they work, a robot's motors get hot enough that heat concerns can limit their performance. To cool down, humans sweat. Now, a robot can do the same.
The conventional way to cool a robot is to either just let the heat dissipate into the air, which doesn't work well because air is a poor conductor of heat. The other solution is to add water cooling, which requires pumps, tubes, and heat-sinks to radiate away the excess heat. Now researchers at the University of Tokyo’s JSK Lab have built a humanoid robot that sweats. Its name is Kengoro.
Kengoro uses his metal skeleton to sweat, and the key is, as ever these days, 3D printing. The Tokyo team 3D printed the metal bones using a process called sintering, in which powder is deposited a layer at a time and cured with a laser. The process allows the designer to vary the porosity of the metal. In the case of Kengoro's bones, they were made to allow water to permeate the metal, seeping out at a rate slow enough not to start dripping, but fast enough to evaporate and carry away excess heat along with it, just like an animal sweating.
"Usually the frame of a robot is only used to support forces," project leader Toyotaka Kozuki told IEEE Spectrum. "Our concept was adding more functions to the frame, using it to transfer water, release heat, and at the same time support forces."
The sintering process is so precise that the porosity can be varied to make permeable channels to guide the water through the skeleton. In tests, Kengoro's cooling system performed three times better than air cooling, as well as beating plain-old water circulation. It doesn't do as well as a dedicated pumped-water-with-radiators setup, but it is also a lot less bulky, and simpler.
One curious side effect of Kengoro's perspiration-based cooling is that it needs to stay hydrated. It doesn't take much, though. Just a cup of water is enough to keep Kengoro and its 108 motors cool all day long.
"In practice," writes Spectrum IEEE's Evan Ackerman, "this means that Kengoro can run at full power longer, letting it do push-ups for 11 minutes straight without burning out its motors."
I can't even imagine 11 straight minutes of pushups, but one thing's for sure. If you managed it, you'd end up smelling a lot worse than Kengoro.