Ballistically launchable shape shifting 3D printed multi-rotor unmanned aerial vehicle design and foldable arms analysis

Abstract

Unmanned Aerial Vehicles (UAVs) have started to play a significant role in military, civil, and commercial sectors with the rapid advancement of modern technology. Particularly in military operations, UAVs used for intelligence, surveillance, and reconnaissance purposes are emerging as an effective technology developed to protect human life. The vehicles used in these areas are typically fixed-wing or rotary-wing and their arms are either rigidly attached to the body or can be manually folded and unfolded. However, manual processes such as folding, propeller and battery installation can lead to time loss in emergency situations. Especially in critical situations where rapid response is required, the length of these preparatory processes can diminish the effectiveness of emergency response and lead to adverse outcomes. This thesis addresses the problem by exploring a UAV design whose arms can fold to fit inside a tube and stand by for ballistic launch within the tube. The research identified the most suitable methodology for UAV production and conducted tests for material selection. The UAV, modeled using SolidWorks' CAD software, is designed to have foldable arms that fit into a launch tube. After production and assembly, ballistic launch tests of the UAV were performed. This drone, referred to as the 'Ballistic UAV (BAL-UAV),' can operate its motors at full thrust to rapidly respond to aerodynamic distortions during unpowered flight and maintain position control. Considering the forces acting on the drone, the maximum force on the arms carrying the drone occurs when the motors operate at full thrust. Thus, Structural Finite Element Analysis (FEA) using ABAQUS was applied to validate the original arm design- the only moving parts of the design- which carries the thrust forces generated by the motors and propellers and to make improvements with alternative designs. Geometric changes and thickness reductions made to optimize the stiffness-to-mass ratio of the arm designs were verified through topology optimization methods. Finally, considering all arm designs and their varying thicknesses, the most optimum design was determined by evaluating the stiffness-to-mass ratio and bending resistance per unit mass of the structural elements. Safety factors were also calculated to determine the safe operating ranges of the arm designs. As a result of these calculations, significant improvements were made to the arm design of the BAL-UAV, reducing the total weight of the drone, and increasing stiffness with different arm designs. This study includes five sections, each outlining the stages of the thesis. In the continuation of the summary, the contents of these sections will be briefly described. The first section begins with a general introduction to the advantages and applications of UAVs in human life. It details how UAVs are categorized into two main types: fixed-wing and rotary-wing, and thoroughly examines the advantages and disadvantages inherent to each type. This section addresses the issue of time loss during pre-flight preparations in emergency situations with UAVs. To solve these problems, the initiation of work on a new type of drone, which can fold its arms to fit into a tube and is ready for ballistic launch within the tube, is mentioned. Additionally, the literature review explores studies in this context, highlighting the use of additive manufacturing technology for producing initial prototypes of drones capable of ballistic launch, a method that facilitates the production of complex geometries and supports rapid prototyping. The first section concludes with a subtitle clearly stating the objective of the thesis. The second section of the thesis concentrates on the design and prototyping processes of the BAL-UAV. Initially, this section discusses the determination of the most suitable methodology to produce the BAL-UAV, highlighting the advantages of this methodology over traditional manufacturing methods. Subsequently, potential materials for production are evaluated, and tensile tests are conducted to validate the choice of materials, with results presented. After material selection, the mechanical design process is explained in detail. This part outlines the considerations during the design process and the requirements that guided the designs. The designs of all mechanical parts are described individually, along with their assembly instructions. The foldable arm design and unfolding mechanism are explained, and the advantages offered by the designed spring mechanism for unfolding are discussed. The selection of motors and factors considered in this process, along with the conducted thrust tests and their results, are detailed. Additionally, the estimation of flight duration based on the results of the thrust tests is included in this section. The final part of the section presents the necessary flight steps for the launch phase of the BAL-UAV, with detailed explanations of these steps. This section provides an in-depth look at every stage of the BAL-UAV's design and prototyping process, reflecting the comprehensive work of the thesis on this subject. The third section of the thesis addresses the FEA and Topology Optimization studies conducted on the BAL-UAV's original arm design and the alternative designs developed. This section initially presents the geometric properties and technical drawings of both the original and alternative arm designs. It examines the geometric changes focused on the parts of the arm design most subjected to axial and bending loads. The process of determining the loading and boundary conditions is detailed. The selection of the element type for creating the finite element model, the mesh generation technique, and the implementation of these techniques are explained. Additionally, the section describes how the design was segmented to create an effective solution mesh. The approach to conducting the mesh convergence analysis and how it was performed to obtain consistent results is emphasized. Finally, the section discusses how the geometric changes and thickness reductions made to optimize the stiffness-to-mass ratio under maximum loading conditions for the arm designs were validated through a topology optimization study. This section thoroughly addresses the analysis and optimization processes of the BAL-UAV's original arm design and alternative designs, providing significant insights into how the designs were made more effective. In the fourth section, a comparative presentation of the analysis results for the BAL-UAV's original arm design and the alternative designs is provided in detail. Initially, the error margins between the Von Mises stresses obtained from the mesh convergence analyses are examined, presenting conclusions about the convergence of the solution mesh. Subsequently, the Von Mises stress values and maximum displacement values for the original arm design are presented. Based on these results, the safety factor of the original arm design is calculated, and the maximum reducible thickness is determined. The benefits of this result on the drone's weight are also discussed. Then, the Von Mises stress values and maximum displacement values for the alternative designs are presented, with the effects of thickness on stress and displacement being compared graphically. The results of the geometric changes and thickness reductions in the designs are compared with the topology optimization results, validate the accuracy of the designs. The factor of safety for all designs are calculated, and designs below the determined safety factor value are identified as unsafe. The masses of the designs with altered geometries and reduced thicknesses are given, and their stiffness and bending rigidity are calculated. Finally, these calculations are used to evaluate the performances of the designs in terms of stiffness-to-mass and bending rigidity-to-mass ratios, identifying the design with the best performance. In the fifth and final section of the thesis, the outcomes of the study are comprehensively evaluated, and suggestions for future work are proposed. The evaluations conclude that a drone design capable of ballistic launch, which can be placed into a launch tube with its foldable arms and transition into stable flight after being launched from stationary or mobile platforms, has been successfully developed. This drone design can perform its tasks in emergencies without the need for preliminary preparations. Particularly, significant improvements made to the arm design, which is a critical component when the drone generates maximum thrust, have led to the optimum arm design. The section also notes plans for future work to enhance the performance of other mechanical components of the drone, aiming to extend flight duration and enable the drone to operate over longer distances. These recommendations encompass studies that would expand the application areas of the BAL-UAV and increase its operational capacity, enabling more effective use in the future.