This paper presents a hybrid pose / wrench control framework for quadrotor helicopters, allowing direct contact of the quadrotor with its environment and stable motion while in contact. The presented work explicitly takes into account the quadrotor's underactuation and utilizes a wrench estimator, able to estimate the wrench generated by the quadrotor using only quadrotor inputs and pose measurements. Experimental results of the quadrotor in pose and hybrid pose-wrench control mode are presented, showing stable behaviour while moving in contact. Whereas a lot of research nowadays is focused mainly on free-flight applications, stable and robust wrench control of quadrotors in direct contact with their environment, opens up new application areas for this class of flying robots.

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Path following deals with the problem of following a geometric path without any preassigned timing information and constitutes an important step in solving the general motion planning problem. The current paper considers path following for differentially flat systems. In this case the dynamics of the system can be projected along the path to a single input system, resulting in a free end-time optimal control problem. We propose to rewrite the problem in terms of the velocity along the path and the path itself. This way, we arrive at a fixed end-time optimal control problem that can be solved efficiently by interiorpoint solvers. Two challenging examples, a truck-trailer parking simulation and a quadrotor mission, illustrate the efficiency of the problem formulation and the practicality of the developed software.

Rigid bodies are essential primitives in the modelling of robotic devices, tasks, and perception. Basic geometric relations between rigid bodies include relative position, orientation, pose, linear velocity, angular velocity, twist, force, torque, and wrench. In Part 1, we explicitly stated the semantics of all coordinate-invariant properties and operations, and, more importantly, all the choices that are made in coordinate representations of these geometric relations. This resulted in a set of concrete suggestions for standardizing terminology and notation. In this tutorial, we show how the proposed semantics allow us to write fully unambiguous software interfaces, including automatic checks for semantic correctness of all geometric operations on rigid-body coordinate representations.