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The main focus of this study is to develop a finite-time super-twisting sliding mode control strategy for the quadrotor based on a higher-order sliding mode observer (HOSMO). 12 state variables are required to describe the motion of the quadrotor, of which six state variables, namely the position, altitude, and orientation, are assumed to be obtained from the sensors. The remaining state variables, i.e. the linear and angular velocities, are determined using the HOSMO. Besides, the HOSMO aids in determining the unknown bounded lumped disturbances acting on the quadrotor. The output of the HOSMO is utilised for implementing the finite-time super-twisting sliding mode controller (FTSTSMC). The proposed FTSTSMC ensures finite-time convergence of tracking error with chattering attenuation. The chattering analysis for a super-twisting algorithm is presented in this work. Moreover, the overall system stability is investigated using the Lyapunov theory, and an expression for the time of convergence of the tracking and estimation error is presented. The effectiveness of the proposed methodology is established using numerical simulations and its performance is compared to a finite-time sliding mode observer coupled with a combination of proportional–integral–derivative and continuous sliding-mode controller. This is then validated in real-time using the DJI Matrice 100.

The quadcopter is a great platform for control systems research as it is highly nonlinear and under-actuated system. The nonlinear dynamic model of the quadcopter is formulated using the Newton-Euler method. The motion of the quadcopter can be divided into two subsystems; a rotational subsystem (attitude and heading) and a translational subsystem (altitude, x and y motion). In this paper two Non-linear Control strategies, sliding mode control (SMC) and Backstepping control (BSC) have been proposed. A SMC is a type of Variable Structure Control. It uses a high speed switching control law to force the state trajectories to follow a specified user defined surface in the states space and to maintain the state trajectories on this surface. BSC is a recursive control algorithm that works by designing intermediate control laws for some of the state variables. These state variables are called "virtual controls" for the system. These Controllers have been implemented on the Quadcopter through simulations using MATLAB/Simulink. The results have been compared with traditional PID controller.