Autonomous reduced-gravity enabling quadrotor test-bed: Design, modelling and flight test analysis

This work establishes conventional quadrotors as viable platforms to produce non-zero reduced-gravity. Toward this, a 1-D vertical manoeuvre with time-varying acceleration is proposed, which when followed by the quadrotor, the on-board payload experiences desired reduced gravity level for a specified time period. Since the proposed manoeuvre involves high axial accelerations and velocities, the standard steady-state thrust model cannot be used. A CFD tool—RotCFD—is used to study the thrust variation of a quadrotor in axial flight, and develop a thrust model. The developed model is experimentally validated through series of axial flight tests. As a consequence of the time varying forces—propeller thrust as well as drag—acting on the quadrotor, a control structure with fixed gains is neither capable of stabilizing the attitude nor maintaining the desired accelerations. A novel method of gain compensation is proposed which stabilizes the quadrotor and ensures quick acceleration convergence to the commanded value. Flight tests results for various reduced gravity levels from 0.8g–0.3g for a time interval of 3 seconds are presented to demonstrate the repeatability and reliability of the proposed control and automation strategies. Experimental results show that g-quality of the order 10 −3 g is achieved.