  For legged robots, aerial motions are the only option to overpass obstacles
that cannot be circumvent with standard locomotion gaits. In these cases, the
robot must perform a leap to either jump onto the obstacle or fly over it.
However, these movements represent a challenge because during the flight phase
the Center of Mass (CoM) cannot be controlled, and the robot orientation has
limited controllability. This paper focuses on the latter issue and proposes an
Orientation Control System (OCS) consisting of two rotating and actuated masses
(flywheels or reaction wheels) to gain control authority on the robot
orientation. Because of the conservation of angular momentum, their rotational
velocity can be adjusted to steer the robot orientation even when there are no
contacts with the ground. The axes of rotation of the flywheels are designed to
be incident, leading to a compact orientation control system that is capable of
controlling both roll and pitch angles, considering the different moment of
inertia in the two directions. We tested the concept with simulations on the
robot Solo12.
