Abhishek

Bio: Abhishek is an academic researcher from Indian Institute of Technology Kanpur. The author has contributed to research in topics: Control theory & Backstepping. The author has an hindex of 7, co-authored 16 publications receiving 138 citations.

Flight dynamics and nonlinear control design for variable-pitch quadrotors

Abstract: This paper introduces the mathematical model for quadrotor with variable-pitch propellers that facilitates generation of negative thrust, thereby augmenting the rate of change of thrust generation suitable for aggressive maneuvering. Blade element theory along with momentum theory is used to estimate aerodynamic loads essential for formulating rigid body dynamics model of the vehicle. Further, the paper develops a nonlinear controller using dynamic inversion technique to stabilize and/or to track a reference trajectory. The controller uses three loops. The outer loop solves the translation dynamics to generate the thrust, pitch angle, and roll angle commands required to achieve a given state or trajectory. Using the commands generated in the outer loop, the inner loop simplifies the rotational dynamics to provide the desired angular velocities. The control allocation loop is added to address the nonlinear relation between control input and rotor thrust and torque. This is done by introducing the derivative of thrust coefficient as a virtual control to the system. These virtual inputs control the derivatives of thrust and body moments, which in turn generates the required thrust and body moments. The performance of the proposed design is shown through simulated results for attitude stabilization and trajectory following.

Robust Attitude Tracking for Aerobatic Helicopters: A Geometric Approach

Abstract: This article highlights the significance of the rotor dynamics in control design for small-scale aerobatic helicopters and proposes two singularity-free robust attitude-tracking controllers based on the available states for feedback. The first employs the angular velocity and the flap angle states (a variable that is not easy to measure) and uses a backstepping technique to design a robust compensator (BRC) to actively suppress the disturbance induced tracking error. The second exploits the inherent damping present in the helicopter dynamics leading to a structure-preserving, passively robust controller (SPR), which is free of the flap angle feedback. The BRC controller is designed to be robust in the presence of two types of disturbance: structured and unstructured. The structured disturbance is due to the uncertainty in the rotor parameters, and the unstructured disturbance is modeled as exogenous torque acting on the fuselage. The performance of the controller is demonstrated in the presence of both types of disturbances through numerical simulations. In contrast, the SPR tracking controller is derived such that the tracking error dynamics inherits the natural damping characteristic of the helicopter. The SPR controller is shown to be almost globally asymptotically stable, and its performance is evaluated experimentally by performing aggressive flip maneuvers. Throughout this study, a nonlinear coupled rotor-fuselage helicopter model with first-order flap dynamics is used.

Control Strategies and Novel Techniques for Autonomous Rotorcraft Unmanned Aerial Vehicles: A Review

Abstract: This paper presents a review of the various control strategies that have been conducted to address and resolve several challenges for a particular category of unmanned aerial vehicles (UAVs), the emphasis of which is on the rotorcraft or rotary-wing systems. Initially, a brief overview of the important relevant definitions, configurations, components, advantages/disadvantages, and applications of the UAVs is first introduced in general, encompassing a wide spectrum of the flying machines. Subsequently, the focus is more on the two most common and versatile rotorcraft UAVs, namely, the twin-rotor and quadrotor systems. Starting with a brief background on the dual-rotor helicopter and a quadcopter, the full detailed mathematical dynamic model of each system is derived based on the Euler–Lagrange and Newton-Euler methods, considering a number of assumptions and considerations. Then, a state-of-the-art review of the diverse control strategies for controlling the rotorcraft systems with conceivable solutions when the systems are subjected to the different impediments is demonstrated. To counter some of these limitations and adverse operating/loading conditions in the UAVs, several innovative control techniques are particularly highlighted, and their performance are duly analyzed, discussed, and compared. The applied control techniques are deemed to produce a useful contribution to their successful implementation in the wake of varied constraints and demanding environments that result in a degree of robustness and efficacy. Some of the off-the-shelf developments in the rotorcraft systems for research and commercial applications are also presented.