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Angelscarf Group

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Slung !NEW!

It shall be unlawful for any person to sell, give away or to have in his possession for the purpose of sale or giving away, or to display for sale or giving away any brass knuckles or other knuckles of metal, slung shot, billy or blackjack. (Code 1962, 27-6)


Abstract:In this paper, a simple active-model-based control scheme is developed for the quadrotor slung load (QSL) system. The scheme works to improve the rejection of the influences caused by the abruptly changed load as a complementary enhancement while maintaining the structure and parameters of the original controller. A linearized model is first constructed with respect to the hovering state of a quadrotor. Modeling error is then introduced to describe the uncertainties caused by the load change and the simplified model. The modeling error is actively estimated by a Kalman filter (KF), while the estimation is further integrated into a normal controller, to enhance its performance of disturbance rejection. Experiments are conducted on a quadrotor controlled by the Pixhawk, which is one of the most popular controllers commercially available on the market. The improvements of the proposed scheme are shown by the comparisons between the controls with and without the active-model-based enhancement. The experiments also indicate that, with its simple structure and less computational algorithm, this active-model-based enhancement would be a feasible approach to enhance the commercial UAV controller to handle more uncertainties.Keywords: quadrotor slung load system; modeling error; active estimation; rapidly-changed load; compensation control; cable-suspended

Any person who carries upon his person, whether concealed or not, or uses or attempts to use against another, any instrument or weapon of the kind usually known as slung shot, or of any similar kind, shall be guilty of a felony.

The ability for a quadrotor with a slung load to perform agile and accurate maneuvers expands the variety of scenarios where load transportation can be applied and enhances its efficiency. Due to the complexity of the system dynamics, slung-load transportation remains a challenging problem, which also causes trajectory generation a time-consuming task. We propose a framework to efficiently generate aggressive load-swing trajectories. Trajectory generation for the load aims to minimize the fifth order time derivative of the load position which, indirectly, minimizes the quadrotor angular velocity actuation. Aggressive load-swing trajectories are obtained by having the constraints for load cable direction embedded into the trajectory generation via constraints on the load acceleration. The trajectory generation, together with an accurate trajectory tracking controller, allows the aggressive maneuvers to be easily performed on the quadrotor with a slung-load. Simulation and experimental results of three dimensional aggressive maneuvers are presented to validate the proposed trajectory generation methodology, including the quadrotor slung-load traversing a window by tilting the cable, and also going through an environment with obstacles that must avoided.

In aerial load transportation applications, knowing the mass of the load in advance is not always possible. The load dynamics depend on its mass and using a high-performance model-based controller with an inaccurate mass will introduce unmodeled disturbances to the system that will negatively affect the closed-loop performance. This paper addresses the design of a trajectory tracking controller for a quadrotor with a slung-load that has an unknown mass. The proposed solution is an adaptive controller with online estimation designed using the backstepping technique. Nonlinear control laws for thrust and angular velocity, and an adaption law for mass estimation are proposed, which guarantee the convergence of the trajectory tracking and the estimation errors to zero, and are robust to variations in load mass. Simulation and experimental results are presented to assess the validity and performance of the proposed controller.

The distinctive pendulum-like oscillation and pitching patterns of cubic and rectangular slung prisms were inspected for two aspect ratios at various Reynolds numbers $Re$ under two free-stream turbulence levels. Systematic experiments were performed using high-resolution telemetry and hotwire anemometry to quantitatively characterize the dynamics of the prisms and the wake fluctuation. The results show that the dynamics of the prisms can be characterized by two distinctive regions depending on the prism shape. Specifically, in the case of cubic prisms the regions are defined by the growth rate of the pitching amplitude; whereas the dynamics of the rectangular prisms is more sensitive to the angle of attack. In particular, when the large side initially faces the flow, the regions are defined by the synchronization between the vortex shedding and pure oscillations under very low turbulence. When the smaller side initially faces the flow, the regions are defined by the equilibrium pitching position. Regardless of the geometry of the prism and flow condition the dominant oscillation frequency resulted as being close to the natural frequency of the small-amplitude pendulum-like oscillation. 350c69d7ab


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