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.
SERVO 12.2016 25
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Image courtesy of JSK Lab/University of Tokyo.