Hexrotor UAV Platform Enabling Dextrous Aerial Mobile Manipulation

Mobile manipulation is a hot area of study in robotics as it unites the two classes of robots: locomotors and manipulators. An emerging niche in the field of mobile manipulation is aerial mobile manipulation. Although there has been a fair amount of study of free-flying satellites with graspers, the more recent trend has been to outfit UAVs with graspers to assist various manipulation tasks. While this recent work has yielded impressive results, it is hampered by a lack of appropriate testbeds for aerial mobile manipulation, similar to the state of ground-based mobile manipulation a decade ago. The Collaborative Mechatronics Lab is addressing this instrumentation gap with the development of a dexterous UAV platform to eventually host a low-cost, lightweight Stewart-Gough platform that can be combined as a macro/micro mobile manipulation system. Based on the concept of force closure (a term from the dexterous manipulation community), the new type of dexterous, 6-DoF UAV provides the unique capability of being able to resist any applied wrench, or generalized force-torque. Typical helicopters or quadrotors cannot instantaneously resist or apply an arbitrary force in the plane perpendicular to the rotor axis, which makes them inadequate for complex mobile manipulation tasks. We have developed a hexrotor UAV that can exert arbitrary wrenches in the 6-DoF force/torque space. In this paper, we describe the importance of force closure for mobile manipulation, explain why it is lacking in current UAV platforms, and describe how our hexrotor provides this important capability as well as exhibiting holonomic behavior. We also describe the results of a staged peg-in-hole task that exerts forces without pitching and rolling the UAV, reducing uncertainties.