18 SERVO 12.2014
With an eye toward making better running robots,
researchers have made surprising new findings about some of
nature's most energy-efficient bipeds: running birds.
Although birds are designed primarily for flight, scientists
have learned that species that predominately live on land and
scurry around on the ground are also some of the most
sophisticated runners of any two-legged land animals. These
characteristics may have been evolving since the time of the
dinosaurs and, some would say transcend the ability of other
bipedal runners, including humans.
In a study published in the Journal of Experimental Biology,
researchers from Oregon State University, the Royal
Veterinary College, and other institutions outline how
running birds have achieved an impressive ability to run while
minimizing energy cost, avoiding falls or injury, and
maintaining speed and direction.
"Birds appear to be the best of bipedal terrestrial
runners, with a speed and agility that may trace back 230
million years to their dinosaur ancestors," said Jonathan
Hurst, an associate professor and robotics expert at the
OSU College of Engineering.
Running birds come in an enormous range of sizes, from
tiny quails to an ostrich that has 500 times as much body
mass. Most — but not all — can fly, but spend a lot of their
lives on the ground, and they don't always look that graceful
when they run. However, researchers found that they
maximize the results while keeping their priorities straight:
Save energy and don't break a leg.
In the wild, an injury could lead to predation and death,
and in like fashion, when food resources are limited economy
of motion is essential.
"These animals don't care that they appear a little
unstable or have a waver in their gait," Hurst said."Their real
goal is to limit peak forces, avoid falling, be safe, and be as
efficient as possible. If their upper body seems to lurch
around a little as a result, that's okay. What they are
accomplishing is really quite elegant."
Even more surprisingly, a wide variety of ground-running
bird species with very different body sizes use essentially the
same strategy to accomplish these sometimes conflicting
tasks. In order to hop over obstacles on uneven ground, they
use a motion that's about 70 percent a "vaulting" movement
as they approach the obstacle, and 30 percent a more
crouched posture while on top of the obstacle.
"Evolution has shaped running birds into all different
sizes and skeletal structures," said Christian Hubicki, a
doctoral student at Oregon State who co-authored the
study."But we found their behavior in how they run is
essentially the same."
In collaboration with Monica Daley at the Royal
Veterinary College in London, the researchers studied five
species of birds and developed a computer model in OSU's
Dynamic Robotics Laboratory that closely matches that
"We should ultimately be able to encode this
understanding into legged robots, so the robots can run with
more speed and agility in rugged terrain," Hubicki said.
"These insights may also help us understand the walking and
running behaviors of all the common ancestors involved,
including theropod dinosaurs such as the velociraptor."
The researchers began the study with a hypothesis that
body stability would be a priority since it might help avoid
falls and leg injuries. That's not what they found, however.
Instead, running birds have a different definition of
stability. They do avoid falls, but also allow their upper bodies
to bounce around some, just so long as they don't tumble.
RUNNING ROBOTS ARE FOR THE BIRDS
Reported by David Stauth