When we use our muscles, they produce heat as a byproduct. When we use them a lot, we need to actively cool them, which is why we sweat. By sweating, we pump water out of our bodies, and as that water evaporates, it cools us down. Robots, especially dynamic robots like humanoids that place near-constant high torque demands on their motors, generate enough heat that it regularly becomes a major constraint on their performance.
Ref: Skeletal Structure with Artificial Perspiration for Cooling by Latent Heat for Musculoskeletal Humanoid Kengoro. 2016 IEEE/RSJ International Conference on Intelligent Robots and Systems.
In this paper we propose a novel method to utilize the skeletal structure not only for supporting force but can also cool by using latent heat. To enable robots using motors to exert great power, cooling the motor is known to be effective to prevent motors from burning out. Considering the fact that the spatial constraint is severe and that the surface of the skeletal structure is not used effectively in humanoid robots, we propose a skeletal structure with bi-layer porous that is fabricated with laser sintering using aluminum, that can not only function as skeletal frame but also help cool the motors by latent heat through artificial perspiration. First we show the detail of the fabrication process of the bi-layer porous structure that prevents water leakage, then we show the strength of the structure, evaluate the cooling effect of the system. In the end the proposed structure is applied to the skeletal frame in musculoskeletal humanoid Kengoro enabling the robot to perform powerful motions under low gear ratio configuration.