Bidirectional Thrust for Multirotor MAVs with Fixed-Pitch Propellers

This paper is devoted to the study of multirotor Micro Aerial Vehicles (MAVs) with fixed-pitch propellers and bidirectional thrust vector. The latter is realized by using dedicated motor controllers, which allow to invert the propellers' direction of rotation during flight (so-called 3D mode), and almost or fully symmetric propellers. We present a unified modeling, controller design, and control allocation approach that accounts for bidirectional thrust. Suitable propellers with the ability to produce thrust and torque in both directions are compared and their parameters are identified through a static thrust test. Furthermore, we discuss applications of bidirectional thrust, like inverted flight or surface slip reduction, which are impossible to realize with common unidirectional thrust vehicles. We generate suitable flight trajectories and evaluate our unified approach in experiments with a custom-built quadrotor.