Sharif Digital Repository

In this thesis an algorithm has been implemented for automatic landing of a quadrotor under the ground effect. In this regard the six degrees of freedom equations of motion using the Newton-Euler method has been designed. Then, the ground effect has been modeled by inspiring from the similar available models in the literature. The proposed models and proportional-integral-derivative attitude control loops have been simulated in MATLAB/Simulink environment. Also, two control strategies, a classical proportional-integral-derivative controller and a sliding mode controller have been utilized for height control loop.Since sliding mode controller requires all state variables to generate control... 

In the class of unmanned air vehicles (UAV), there is a class entitled as Quad-rotor that engineers pay much attention due to specific features to them. Main applications of this class are because of vertical take-off and landing capability and high controllability. This class has high controllability in environments with high barriers because of the inherent imbalance. All of the Quad-rotors have already studied, had a fixed structure. So the designer's main focus was on improving the guidance and control systems and almost all forms of linear and nonlinear control methods and fuzzy, adaptive and robust control have been investigated. In this study variable structure is examined instead... 

In recent years، one of the most popular and wide areas of research have been focused on Unmanned Aerial Vehicles (UAVs). Among them، Quadrotor which has the capability of Vertical Take-off and Landing (VTOL)، hovering، great agility and maneuverability، simple structure، light weight and reasonable size has particular importance. In the industry، we always deal with plants which there are no precise information about their dynamic model، or their model is too complex to identify. So designing controllers with less dependency to system model and no need to exact knowledge of the system is absolutely vital. The arrangement of motors in a Quadrotor provides six Degree Of Freedoms (DOF) for... 

In recent years, autonomous unmanned aerial vehicles (UAVs) have attracted considerable amount of interest because of a wide area of applications and a lot of advantages. UAVs have been extensively used for military operations that include tracking, surveillance, active engagement with weapons and airborne data acquisition. UAVs are also in demand commercially due to their advantages in comparison to manned vehicles. These advantages include lower manufacturing and operating costs, flexibility in configuration depending on customer request and not risking the pilot on demanding missions. Quadrotor, which is a kind of rotary wing UAVs, has many advantages such as the vertical take-off and... 

Design and development of Unmanned Aerial Vehicles (UAVs) has been a hot topic in the past decades. In particular, Vertical Take Off & Landing Vehicles (VTOLs) have been extensively studied and are under constant development. Quad rotors are one of the major subcategories of VTOLs and a lot of effort have been devoted to their control optimization. In the present study, we have utilized a novel transformer quad rotor structure that can change the angle between its arms. This structural change is a type of design feature modification that can effect the moments of inertia by changing the flight dynamics of quad rotor. Modification of height difference between adjacent rotors, while avoiding... 

A new heuristic controller, called nonlinear model predictive control based on gravitational search algorithm, is proposed for nonlinear systems. Nonlinear model predictive control involves the solution at each sampling instant of a finite horizon optimal control problem subject to nonlinear system dynamics and constraints. The new controller formulates nonlinear model predictive control problem as a single stochastic dynamic optimization problem and uses a system of virtual masses to find the best control signal at each sampling instant. For this purpose, a cost function is defined to evaluate each point of the search space. This function minimizes simultaneously the tracking error, control... 

In this study, in order to enhance the accuracy of tracking repetitive maneuvers in Unmanned Aerial Vehicles (UAVs), an educable control scheme is proposed. At the outset, the controller is designed based on the sliding mode control (SMC) technique. In addition, the offline PD-type memory-based iterative learning control (ILC) is used along with SMC. In ILC scheme, the error of states is saved during the maneuvers that will be used in the subsequent iteration. Also, in order to increase flexibility of the new control structure, ILC-SMC, a multilayer perceptron has been developed. This network is designed to extend the control signal, generated by ILC, to similar maneuvers. The presented... 

In this research, the dynamic model of a quadrotor-cable airborne wind energy system is presented. These systems have received a lot of attention in recent years and many examples of them have been designed and built. In addition to comprehensive system modeling, cables and quadrotor in the quasi-stable autorotation phase are modeled separately. These models can be used in other fields in addition to wind energy systems. One of the applications of this thick cable model is in the marine industry.In this research, Newton-Euler method has been used for modeling. The cable model is considered and developed as rigid elements with joints with rotary springs and dampers. The quadrotor model is... 

As the leading kind of multi-rotors, quadrotors have become one of the most popular Unmanned Areal Vehicles (UAVs). These robots are very agile, but their speed is limited when performing decent maneuvers. In this project, a special quadrotor with dihedral-rotating arms is presented in order to increase the decent velocity of the vehicle. The conceptual and detailed designs of the vehicle are presented first, followed by the construction of the quadrotor. The fabricated quadrotor measures 25 cm in size, has a weight of about 1 kg, and can support up to 70 degrees of dihedral angle. Afterwards, the dynamic equations of the dihedral quadrotor are driven and simulated. The effects of dihedral... 

It is well-known that helicopters descending fast may enter a region in the velocity space called Vortex Ring State where the blade’s lift differs significantly from regular regions and includes high amplitude fluctuations. These fluctuations may lead to instability and therefore, this region is avoided, typically by increasing the horizontal speed. However, this region is not fully identified for multirotors, which their blades are rigid in contrary of helicopter’s blades which have two degrees of freedom. This project researches this phenomenon in the context of small-scale quadcopters. The region corresponding to the VRS is identified by combining first-principles modeling and wind-tunnel... 

Proportional-Integrator-Derivative (PID) controller is used in a wide range of industrial and experimental processes. There are a couple of offline methods for tuning PID gains. However, due to the uncertainty of model parameters and external disturbances, real systems need more robust and reliable PID controllers. A compelling example of these types of systems is Quadrotor. In this article, a self-tuning PID controller using Reinforcement Learning for attitude control of a quadrotor has been investigated. In the proposed method, an Incremental PID, which contains constant and variable gains, has been used, and only the variable ones have been tuned.In this research, the model-free... 

Quadrotors have limitation in performing fast descending maneuver due to entering a dangerous region in velocity space called Vortex Ring State(VRS) which cause considerable loss of lift that may lead to fall. The purpose of this project is to reduce time of fast descending maneuver without entering VRS region by using model predictive control. First, appropriate nonlinear dynamic model of quadrotor obtained by considering important aerodynamics effect. Then by considering velocity constraints in order to avoid entering the VRS region, a nonlinear model predictive controller(NMPC) has designed. This controller successfully reduce the time of the maneuver up to than ordinary descending.... 

Quadrotors have limitation in performing fast descent maneuvers due to Vortex Ring State (VRS) region which make quadrotor unstable. In order to avoid entering VRS, a velocity constraint considered which it should be satisfied during this maneuver to guarantee a safe and stable fast descending maneuver by quadrotor. The purpose of this thesis is to overcome limitation in speed space of quadrotor in order to reduce the time of fast descending maneuvers by using Reinforcement Learning Techniques. A new cascade controller proposed which using PID in inner loop as a low level controller and DDPG as one of reinforcement learning techniques in outer loop as high level controller in order to...