Servo - May 2015

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 grasping end-effector.

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 behaviors.

"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 innovate.