  The general problem of planning feasible trajectories for multimodal robots
is still an open challenge. This paper presents a whole-body trajectory
optimisation approach that addresses this challenge by combining methods and
tools developed for aerial and legged robots. First, robot models that enable
the presented whole-body trajectory optimisation framework are presented. The
key model is the so-called robot centroidal momentum, the dynamics of which is
directly related to the models of the robot actuation for aerial and
terrestrial locomotion. Then, the paper presents how these models can be
employed in an optimal control problem to generate either terrestrial or aerial
locomotion trajectories with a unified approach. The optimisation problem
considers robot kinematics, momentum, thrust forces and their bounds. The
overall approach is validated using the multimodal robot iRonCub, a flying
humanoid robot that expresses a degree of terrestrial and aerial locomotion. To
solve the associated optimal trajectory generation problem, we employ ADAM, a
custom-made open-source library that implements a collection of algorithms for
calculating rigid-body dynamics using CasADi.
