  This paper considers a class of rotary-wing aerial robots with unaligned
propellers. By studying the dynamics of these vehicles, we show that the
position and heading angle remain flat outputs of the system (similar to
conventional quadrotors). The implication is that they can be commanded to
follow desired trajectory setpoints in 3D space. We propose a numerical
strategy based on the collocation method to facilitate the trajectory
generation. This enables convenient computation of the nominal robot's attitude
and control inputs. The proposed methods are numerically verified for three
multirotor robots with different dynamics. These include a tricopter with a
tilting propeller, and a quadrotor and a hexacopter with unparalleled
propellers.
