  This paper presents the modeling and numerical analysis of the Kangaroo lower
body prototype, a novel bipedal humanoid robot developed and manufactured by
PAL Robotics. Kangaroo features high-power linear electric actuators combined
with unique serial-parallel hybrid chains, which allow for the positioning of
all the leg actuators near the base of the robot in order to improve the
overall mass distribution. To model and analyze such complex nonlinear
mechanisms, we employ a constrained formulation that is extended to account for
floating-base systems in contact with the environment. A comparison is made to
demonstrate the significant improvements achieved with TALOS, another humanoid
bipedal robot designed by PAL Robotics, in terms of equivalent Cartesian
inertia at the feet and centroidal angular momentum. Finally, the paper
includes numerical experiments conducted through simulation and preliminary
tests performed on the actual Kangaroo platform.
