bots IN BRIEF
SERVO 12.2014 17
We’re all used to seeing two basic types of hovering
robots. The first type is the more traditional helicopter
design with a single main rotor (or two) and maybe a little
tail rotor. The second type is the pervasive quadcopter (or
hexacopter or octocopter or whatever). With a helicopter,
you have to manage a very complex multiple-actuator linkage
system for control and stability, and quadcopters have at least
as many motors as they do rotors.
The Modular Robotics Laboratory at the University of
Pennsylvania has been seeing what it takes to reduce both
the complexity and number of actuators of rotorcraft, and
they’ve come up with some very cool solutions.
To clarify what’s going on here, the rotor at the top (the
bottom one is fixed) has to alter its angle of attack every
single time it spins around — which is 40 times every second.
It’s a complex thing to control, and if you’re trying to do it with just
one motor you have to somehow manage to make it work with the
only thing you do have control over: the acceleration of said motor.
By reducing the number of motors and actuators, the price of the
robot drops drastically, plus, its weight goes down and endurance goes
up making it much more versatile.
Part of what makes snakes so
adaptable is how they can choose
from a variety of gaits depending
on what they’re trying to do or
where they’re trying to go. Robot
snakes can do this too, and in some
ways they can do it even better because they can execute
behaviors that real snakes don’t know how to do — like
rolling longitudinally to climb up poles.
However, we still have a lot to learn about how and why
snakes move the way they do. In the latest issue of Science,
researchers from Georgia Tech, roboticists from Carnegie
Mellon, and herpetologists from Zoo Atlanta describe how
sidewinders climb up steep sandy slopes, and show how snake
robots can learn from their technique.
When a sidewinder moves, the
parts of its body that are in contact
with the ground remain still. This
helps to minimize slip — especially
on loose surfaces like sand or dirt.
The value of this technique
increases as the slope increases,
since slipping becomes more likely.
The researchers want to figure out
exactly how the snakes would
change their gaits to better adapt
to steeper slopes.
High speed footage of six adult
sidewinders from Zoo Atlanta
revealed that the snakes would progressively increase the
length of their bodies in contact with the sand as the slopes
got steeper (up to 20 degrees of incline), keeping themselves
stable. Other kinds of pit vipers who didn’t use this
sidewinding motion would tumble down the hill instead.
Snake robots are versatile and durable, and teaching them
to climb steep slopes covered in loose granular material
seems like it would come in especially handy somewhere like,
say, Mars. Yep, we’re talking about snake robots in space.
Images courtesy of University of Pennsylvania MODLAB.
PROPS TO BETTER DESIGNS
ON STEEP SANDY