  We design, build, and thoroughly test a new type of actuator dubbed
viscoelastic liquid cooled actuator (VLCA) for robotic applications. VLCAs
excel in the following five critical axes of performance: energy efficiency,
torque density, impact resistence, joint position and force controllability. We
first study the design objectives and choices of the VLCA to enhance the
performance on the needed criteria. We follow by an investigation on
viscoelastic materials in terms of their damping, viscous and hysteresis
properties as well as parameters related to the long- term performance. As part
of the actuator design, we configure a disturbance observer to provide
high-fidelity force control to enable a wide range of impedance control
capabilities. We proceed to design a robotic system capable to lift payloads of
32.5 kg, which is three times larger than its own weight. In addition, we
experiment with Cartesian trajectory control up to 2 Hz with a vertical range
of motion of 32 cm while carrying a payload of 10 kg. Finally, we perform
experiments on impedance control and mechanical robustness by studying the
response of the robotics testbed to hammering impacts and external force
interactions.
