18 SERVO 02.2014
Robonaut 2's space legs have been a not-secret since astronaut
Rick Mastracchio posted a picture of them on Twitter last year. Since
then, pictures have popped up all over the place, but what we haven't
seen is much in the way of footage of Robonaut legging itself around.
Finally, there’s a video (see link below) which can be summarized in one
These legs are not for walking, obviously, because Robonaut is
designed for space where it doesn't need legs that'll be able to
successfully stand up to gravity. Rather, Robonaut's legs are more like
secondary arms with secondary hands that the robot will use to climb
around the outside of the International Space Station, and to hold itself
in place as it works with its primary arms and hands.
With its seven-jointed legs fully extended, Robonaut can span a gap
of nearly three meters. Cameras and grippers on the ends of the legs
lets the robot see where it's grabbing, and there are already plenty of
rails and sockets on the ISS to help Robonaut get from place to place.
The legs will be functional inside the station as well, and the
Robonaut torso currently on duty in space is scheduled to receive this
upgrade early next year.
GETTING ITS WATER LEGS NINJA STYLE
These new amphibious legs from McGill University roboticists
— the creators of the Aqua robot — are called "Ninja legs" because
the researchers figure that "the design resembles a spinning ninja
star." Essentially, Ninja legs are flippers that can flex up to 120
degrees, each contained inside a carbon fiber and spring steel frame
that are mounted on Aqua's rotary leg joints. On land, the frame
works just like a leg; while in the water, the frame allows the flipper
inside it to move freely, resulting in efficient swimming.
As is usually the case when you take two very different things
and combine them into one thing, the Ninja legs involve some
compromises. The most obvious disadvantage is perhaps complexity, and the
efficiency for both walking and swimming decreases relative to legs that are designed
and optimized specifically to perform one of those tasks. This decrease is not nearly
as bad as might be expected, though.
For walking gaits, the Ninja legs require perhaps 15 to 20 percent more power
to rotate at a given frequency, but they can also achieve higher stable speeds due to
higher inherent compliance. As for swimming, the Ninja legs hit a sweet spot at a 2. 5
Hz oscillation frequency and 50 degree oscillation amplitude where they produce
nearly as much thrust as flippers can ( 35 N as opposed to 40 N).