Servo - December 2016

PUSH-UPS?

NO SWEAT!

When we humans use our muscles, we produce heat as a by-product. 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. 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 becomes a major constraint on their performance.

Engineers solve this heat-generating problem in most mechanical systems by using fans, heatsinks, and radiators, which means that you’ve got all of this dedicated cooling infrastructure that takes up space and adds mass. However, Japanese researchers presented a novel idea at a recent conference of how to cool humanoid robots in a much more efficient way: Design them to be able to sweat water The researchers from the University of Tokyo’s JSK Lab, led by Professor Masayuki Inaba, were trying to figure out how to add a cooling system to their 1.7 meter tall, 56 kilogram musculoskeletal humanoid named Kengoro (who joins Kojiro and Kenshiro as part of the JSK robot family). Kengoro is already stuffed to the brim with structural components, circuit boards, gears, and 108 motors, and there was simply no room to add active water cooling with tubes and a radiator and fans. The researchers started looking at how they could make better use of Kengoro’s existing components, and they came up with the idea of using the robot’s skeletal structure (its metal frame) as a coolant delivery system. The approach goes way beyond just running water channels through the frame and circulating water through them since that wouldn’t have solved the problem of needing to place a radiator in there somewhere. The researchers instead decided to try a passive technique, allowing the water to seep out through the frame around the motors to cool them evaporatively. In other words, Kengoro sweats.

Kengoro can run for half a day on about a cup of de-ionized water and it has to keep itself hydrated for the cooling to be effective, especially if it’s working hard — just like with us. Testing shows that this method of cooling works three times better than air cooling, and is significantly better than just circulating water through the interior channel (although it’s not as effective as a traditional radiator using active cooling.) In practice, this means that Kengoro can run at full power longer, letting it do push-ups for 11 minutes straight without burning out its motors.