  This paper describes the control, and evaluation of a new human-scaled biped
robot with liquid cooled viscoelastic actuators (VLCA). Based on the lessons
learned from previous work from our team on VLCA [1], we present a new system
design embodying a Reaction Force Sensing Series Elastic Actuator (RFSEA) and a
Force Sensing Series Elastic Actuator (FSEA). These designs are aimed at
reducing the size and weight of the robot's actuation system while inheriting
the advantages of our designs such as energy efficiency, torque density, impact
resistance and position/force controllability. The system design takes into
consideration human-inspired kinematics and range-of-motion (ROM), while
relying on foot placement to balance. In terms of actuator control, we perform
a stability analysis on a Disturbance Observer (DOB) designed for force
control. We then evaluate various position control algorithms both in the time
and frequency domains for our VLCA actuators. Having the low level baseline
established, we first perform a controller evaluation on the legs using
Operational Space Control (OSC) [2]. Finally, we move on to evaluating the full
bipedal robot by accomplishing unsupported dynamic walking by means of the
algorithms to appear in [3].
