Cable-suspended load lifting by a quadrotor UAV: hybrid model, trajectory generation, and control
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In the last years, autonomous aerial vehicles have become promising mobile robotic platforms capable of manipulating external objects. In particular, quadrotors, rotorcrafts with four propellers, have been used for aerial transportation of cable-suspended loads. A critical step before transporting a payload is the lift maneuver. However, the analysis and planning of this maneuver have received a little attention in the literature so far. In this work, we decompose the cable-suspended load lifting into three simpler discrete states or modes: Setup, Pull, and Raise. Each of these states represents the dynamics of the quadrotor-load system at particular regimes during the maneuver. Furthermore, we define a hybrid system based on these states and show that it is a differentially-flat hybrid system. Exploiting this property, we generate a trajectory by using a series of waypoints associated with each mode. We design a nonlinear hybrid controller to track this trajectory and therefore execute the lift maneuver. We verify the proposed approach by carrying out experiments on an actual quadrotor with a cable-suspended load.
KeywordsAerial transportation Lift maneuver Hybrid systems Differential flatness Trajectory generation
This work was supported in part by the Army Research Lab Micro Autonomous Systems and Technology Collaborative Alliance (ARL MAST-CTA #W911NF-08-2-0004). We would like to thank the Ecuadorian scholarship program administrated by the Secretaría de Educación Superior, Ciencia, Tecnología e Innovación (SENESCYT) for providing part of the financial support for P. J. Cruz. We gratefully acknowledge Prof. Meeko Oishi from UNM for numerous discussions and her invaluable feedback about the hybrid model. Special thanks to Christoph Hintz for his help in recording the experimental tests.
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