Go for a walk?
Motors, springs, cables, and the right model could open the door to walking robots.
The left and right sides of the BiMasc walker with labels identifying components.
The left and right sides of the BiMasc walker with labels identifying components.
"Cables are a nontraditional approach to robot
design," says Hurst. "But they let us mount the
springs on the walker rather than on the leg segments where they would have to travel back and
forth with the walker's movements."
Hurst's goal is to build a dynamically simple
walker, one that almost walks itself on flat, level
ground. He notes that some engineers have built
passive dynamic walkers that have no power
source, just properly distributed masses and linkages. These devices have a slow but natural walking gaits when traveling down a slight hill. "I'd like
to take that idea and wrap a good control system
around it," he says.
The software and controls involved in walking
are relatively straightforward. But they get more
complicated when handling disturbances such as
bumps in the road, strong winds, or perhaps inclines. So Hurst is looking for a simple mathematical
model of walking with known natural dynamics.
Then controls for BiMasc can take advantage of
those natural dynamics.
"I want the robot to be good at walking and running over a variety of terrains. If it looks human or
animallike when it runs, it would be a fortunate coincidence, not a goal," says Hurst. This project is not
about biokleptics, a term I've heard which refers to
taking ideas from biology to use in robotics."
Currently, Hurst is developing a controller to
handle running. Next come experiments to find the
optimal stiffness or compliance for running. During
these trial runs, all parameters for the gait will stay
constant, except for stiffness. For example, speed,
stride length, and maximum height will be held the
same as Hurst changes the stiffness (through the
smaller pretensioning motor). Hurst will also measure how much energy BiMasc is using. If his theory
is correct, Hurst will find a specific stiffness that
corresponds to the best efficiency (least energy
used.).
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Who needs a walking robot? People with problems walking, including the
aged, could also use exoskeletons for getting
around. "If we build a device that works with
the body's natural biomechanics rather than
fight them, we could assist a lot of people with
disabilities by using only a small amount of additional energy." One of the few ways to make mobile robots
compatible with spaces designed for humans is
to give them legs, says Hurst. "Wheeled robots
are fine for roads and even some fairly rough terrain," he says. "But they can't climb stairs and
have problems in narrow corridors. "It may take time, but eventually humans will
be working with robots," he continues, "We'll
want to do that on an eye-to-eye level, so they
will have to be tall and thin. "Eventually, we will have walking, humanoid robots," insists Hurst. "People want it to happen, so it will." |
Hurst is working on his bipedal robot with help from his adviser, Al Rizzi, as well as Professors Jessy Grizzle and Ben Morris at the University of Michigan. Funding is through the National Science Foundation.
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