  Walking quadruped robots face challenges in positioning their feet and
lifting their legs during gait cycles over uneven terrain. The robot Laika is
under development as a quadruped with a flexible, actuated spine designed to
assist with foot movement and balance during these gaits. This paper presents
the first set of hardware designs for the spine of Laika, a physical prototype
of those designs, and tests in both hardware and simulations that show the
prototype's capabilities. Laika's spine is a tensegrity structure, used for its
advantages with weight and force distribution, and represents the first working
prototype of a tensegrity spine for a quadruped robot. The spine bends by
adjusting the lengths of the cables that separate its vertebrae, and twists
using an actuated rotating vertebra at its center. The current prototype of
Laika has stiff legs attached to the spine, and is used as a test setup for
evaluation of the spine itself. This work shows the advantages of Laika's spine
by demonstrating the spine lifting each of the robot's four feet, both as a
form of balancing and as a precursor for a walking gait. These foot motions,
using specific combinations of bending and rotation movements of the spine, are
measured in both simulation and hardware experiments. Hardware data are used to
calibrate the simulations, such that the simulations can be used for control of
balancing or gait cycles in the future. Future work will attach actuated legs
to Laika's spine, and examine balancing and gait cycles when combined with leg
movements.
