bots IN BRIEF
16 SERVO 11.2015
OUT OF THE FRYING PAN, INTO THE FIRE
Abimetal consists of two different kinds of metal stuck together. Bimetals are different than alloys, where the two metals are blended; in a bimetal,
the two metals are just layered on top of each other. The reason to do this is
to take advantage of the different characteristics of different metals when
they’re heated. They expand at different rates, causing the piece of bimetal to
deform until it cools off again.
Essentially, a bimetal is a way to convert heat directly into mechanical
energy, and researchers at the University of Tokyo have come up with a way to
leverage this to get a robot to walk. The robot — called Thermobot — has no
sensors and no actuators, and as long as it’s got a hot surface to walk on, it
can keep going pretty much forever.
The trick to this is a combination of
two things. First, Thermobot’s feet are
heavily weighted at the backs, meaning that
when the bimetal on one foot deforms and
the robot rocks sideways, the foot swings
forward. At the same time, the weights on
Thermobot’s legs control the distance that
the robot tips laterally. If everything is
calibrated properly, Thermobot will tip back
onto the swinging foot when it’s ahead of
the body and the robot has taken a step.
It’s important to note that this
technique won’t work in an environment
that’s hot overall. The surface has to be
significantly hotter ( 50 degrees Celsius,
ideally) than the rest of the environment in
order to give the bimetal a chance to cool
so the cycle can repeat itself. In this particular case, Thermobot is walking on a hot plate
that’s 170 degrees C in a 26 degree room. However, it doesn’t matter that much what the
absolute temperatures are, just that there’s a significant relative difference between them.
Thermobot is quite happy to walk in 300 degrees C temperatures as long as the surface is
hotter than ambient.
This is certainly one of the more novel walking techniques — especially since it’s able to
walk on a level surface by harvesting heat. However, no practical applications immediately
come to mind. Researchers say they’re working on combinations of metals that will allow
Thermobot to operate at much lower temperatures — perhaps even safe temperatures —
and that it might make for a pretty cool toy. They’re also going to be working on “other
locomotion mechanisms that can be realized using the self-oscillation of bimetal sheets.”
Perhaps we’ll see more creative robots making use of this tech in the near future.