Hybrid force/motion control and internal dynamics of quadrotors for tool operation

This paper presents a hybrid force/motion control framework for quadrotors with a rigid/light tool attached on it. By transforming the quadrotor dynamics into that of the tool-tip position y and applying the passive decomposition to decompose its dynamics into tangential and normal components w.r.t. a contact surface, we design hybrid position/force control. We also elucidate the internal dynamics (i.e., the dynamics hidden from the tool-tip position and yaw angle output and not directly affected by the control action due to the quadro-tor's underactuation), reveal a (seemingly counter-intuitive) necessary condition for internal stability (i.e., tool above the quadrotor, not beneath it), and propose a stabilizing control action to ensure the angular rates still be bounded while preventing the finite-time escape. Simulations are performed to support the theory.