Due to the robotics and programming that make the
three-legged stance possible, there is no calculable scenario;
no dynamics where the robot could or would topple. "That
is the deliberate aspect of the design. It could stop moving
at any time and sit there indefinitely if it is confused or
whatever," Kennedy said.
Using the three-legged stance, RoboSimian has a single
limb remaining free that can operate as an arm and
Kennedy and his colleagues write the RoboSimian
software in the popular C programming language. It is
nearly all custom written code in C, according to Kennedy.
All the commands are based in achieving intent by using
any of a number of established programmed robotic
"Those might be, walk from point A to point B, or turn
the valve. The DARPA Challenge dictates all the behaviors
and tasks the robot must have the capacity to perform,"
stated Kennedy. Supportive behaviors include sitting,
grasping, turning, and many others.
The communications protocol between the robot and
the human controller is Wi-Fi.
Deliberate and Stable vs.
Dynamic and Reactive
The deliberate and stable approach to RoboSimian has
advantages over the more obvious dynamic and reactive
approach that other roboticists use. Operating with the
given that in the DARPA Challenge, human operators will
have to pause robotic movements and applications while
they consider their next move, Kennedy and colleagues
knew there will be times when the robot
will need to simply stop moving and hold
its position for indefinite periods of time.
"You don't want the robot burning power
or getting in trouble in those intervals. And
you don't want the robot making
mistakes," Kennedy said.
Another important reason for taking
the deliberate and stable path is that it is
much more difficult to figure out what
went wrong with learning algorithms than
with the kinds of software and algorithms
that RoboSimian uses. "If RoboSimian does
do something that is bad, we will figure
out exactly what the robot was thinking at
that point, and see what comes out the
other end, and why that was not what we
wanted. The retrieval of state is what you
want here," commented Kennedy. The
deliberate and stable approach of RoboSimian is similar to
what the Mars rovers applied, and that is why NASA could
diagnose issues so well with the Rovers so far away on
Mars, according to Kennedy.
A deliberate and stable robot equipped with multi-jointed limbs makes for broad capabilities. "Every limb is
designed for manipulation and mobility, and they are all
identical — each with seven joints," said Kennedy. The seven
joints enable seven independent rotations which end up
being and accomplishing the same things that a human
arm can do, though they are set up differently. "RoboSimian
has the same number of rotations, but these are distributed
along the limb in the joints," Kennedy explained.
The RoboSimian's joints use brushless motors with
brakes and encoders, including output encoders to sense
the angle of the joint. The motors drive harmonic drives
that are typical in robotics applications. "These drive trains
are deployed with cartridges such that if an actuator fails,
we can slide it out and replace it with another, and screw
that in," stated Kennedy.
An important part of the technology is the fact that
the limbs and joints are very generalized, so operators who
find different ways to use the robot to do things can count
on the ability for the robot to fulfill those expectations
without changing the hardware. "For example, last year we
had added a mode where the robot can sit down, and we
can use the upper limbs to do manipulation. This also freed
up the lower limbs to do a forklift mode where we slide the
lower limbs into something and pull it out like they would
using a forklift," said Kennedy. So, the generalization of the
hardware capabilities enables the human operators to
12 SERVO 05.2015
RoboSimian's inner workings.
RoboSimian is a robot that avoids trial-and-error learning
in order to avoid making mistakes.