STAR POWER
This little guy from UC Berkeley's Biomimetic Millisystems
Lab is called STAR for Sprawl-Tuned Autonomous Robot — a
six-legged skittery thing just 12 cm in size that can adapt its
limbs and its gait to zip over and under obstacles. More info on
STAR is scheduled to be presented at ICRA 2013 in Germany
in May.
The robot can achieve legged performance over rough
surfaces and obstacles using a high sprawl angle, and nearly
wheel-like performance over smooth surfaces for small sprawl
angles. By changing the sprawl angle, it can climb over obstacles
or crawl underneath them. STAR can run at 5. 2 m/s ( 43 body lengths/second, Froude number 9. 8) over a smooth surface,
which makes it the fastest untethered crawling robot.STAR was developed by David Zarrouk,Andrew Pullin, Nick Kohut, and
Ronald Fearing. Check it out at http://robotics.eecs.berkeley.edu/~ronf/Biomimetics.html#NEW.
GONE BATTY
Bats are awesome. They are spectacular fliers, and
roboticists can learn a lot from them. Problem is, real
bats are more interested in catching and eating a
bellyfull of bugs than sitting still while biologists fiddle
with high speed cameras and x-ray machines and
whatnot. The solution, of course, is a robot.
Brown University's robotic bat wing can't quite fly
(not by itself, anyway), but it does a great job of
pretending. With three servos, seven movable joints,
and bones 3D printed to match the real thing, the wing
can match the basic flight parameters of bats well
enough to allow biologists to measure energy
consumption. By tweaking these parameters, it's
possible to see what sort of flight techniques make a
difference, and then use this data to inform future wing
designs for flapping wing UAVs.
One experiment looked at the aerodynamic effects of
wing folding. Bats (and some birds) fold their wings back
during the upstroke. Previous research from Brown had found
that folding helped the bats save energy, but how folding
affected aerodynamic forces wasn't clear. Testing with the
robot wing shows that folding is all about lift.
In a flapping animal, positive lift is generated by the
downstroke, but some of that lift is undone by the
subsequent upstroke which generates negative lift. By running
trials with and without wing folding, the robot showed that
folding the wing on the upstroke dramatically decreases that
negative lift, increasing net lift by 50 percent.
As it turns out, the robot wing breaks a lot, but even
that's a learning experience, according to Brown grad student
Joseph Bahlman.
During testing, for example, the tongue and groove joint
used for the robot’s elbow broke repeatedly. The forces on
the wing would spread the groove open, and eventually break
it open. Bahlman wrapped steel cable around the joint to
keep it intact — similar to the way ligaments hold joints
together in real animals.
The fact that the elbow was a characteristic weak point
in the robot might help to explain the musculature of elbows
in real bats. Bats have a large set of muscles at the elbow that
are not positioned to flex the joint. In humans, these muscles
are used in the motion that helps us turn our palms up or
down. Bats can’t make that motion, however, so the fact that
these muscles are so large was something of a mystery.
Bahlman’s experience with the robot suggests these muscles
may be adapted to resist bending in a direction that would
break the joint open.
The researchers plan to start figuring out all of the
complex relationships between flapping frequency, flapping
amplitude, flapping angle, wing downstroke time, and wing
folding, and also what's energy efficient and what's not. Then,
they can start messing with things, swapping out materials and
structures to improve on the real thing. If they could teach
the resulting robot to survive on insects, they'd be totally set.
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