  Wheeled-legged robots combine the efficiency of wheeled robots when driving
on suitably flat surfaces and versatility of legged robots when stepping over
or around obstacles. This paper introduces a planning and control framework to
realise dynamic locomotion for wheeled biped robots. We propose the Cart-Linear
Inverted Pendulum Model (Cart-LIPM) as a template model for the rolling motion
and the under-actuated LIPM for contact changes while walking. The generated
motion is then tracked by an inverse dynamic whole-body controller which
coordinates all joints, including the wheels. The framework has a hierarchical
structure and is implemented in a model predictive control (MPC) fashion. To
validate the proposed approach for hybrid motion generation, two scenarios
involving different types of obstacles are designed in simulation. To the best
of our knowledge, this is the first time that such online dynamic hybrid
locomotion has been demonstrated on wheeled biped robots.
