Autonomous Mars-Gravity Enabling Quadrotor

Abstract

Study of various physical phenomena in reduced gravity environments is of importance to several branches of science. This paper describes the trajectory design and automation control strategy for a quadrotor to maintain an acceleration such that a payload on-board experiences Mars-gravity for a short time period. A 1-D vertical trajectory with time varying acceleration is proposed for this purpose. A detailed kinematic analysis is presented to arrive at an acceleration schedule for the quadrotor to follow this trajectory. The analysis will also enable a designer to choose an appropriate motor-propeller combination for a quadrotor to follow this trajectory, given the constraints on peak altitude of the executed trajectory and duration for which reduced gravity needs to be maintained. The efficacy of the proposed approach and automation strategy is demonstrated using a detailed 6-DoF model simulation. Since the proposed trajectory is highly unsteady, the widely used steady state thrust model for quadrotors will not suffice. Therefore, a better thrust model is developed using blade element theory where the model parameters are estimated using experiments conducted in a wind tunnel. Our kinematic analysis shows that an appropriately designed quadrotor is capable of replicating Mars gravity environment for duration of 4 seconds while executing a vertical trajectory with peak altitude less than 45 m, which is validated through simulation and a preliminary flight test.