Design, Rapid Prototyping and Testing of a Ducted Fan Micro-Quadcopter

This paper discusses recent results toward the design, rapid prototyping and testing of a ducted microquadcopter. Mobility and convenience objectives of this work dictate that the quadcopter must fit into a pocket, be capable of shooting high-definition videos and pictures, be controllable through a smartphone application, have a rotor diameter of 7cm and weigh approximately 300 g. Previous designs have rotor dimensions of 25 cm or more as well as airframe width and length of 75 cm and above. Aerodynamically, the ducted fan design is analyzed through Momentum Theory and Blade Element Momentum Theory (BEMT) to determine its contribution toward improved performance in hover, axial climb, axial descent and forward flight. The ducted fan design can be optimized for lower power consumption of up to 30% or smaller diameter than an open rotor and improves hover performance most significantly. Individual components, including the upper ducted and lower airframe were fabricated using composite layup methods. Microrotors as well as ducted fan molds were designed and built through three-dimensional (3D) Printing methods, including the Fused Deposit Modeling (FDM) and the PolyJet (PJ) method. Careful attention was taken to patch the duct lips with composites and sanding them to ensure smoothness. It was found that microrotors have to have at least a 4% thickness-to-chord ratio in order to be structurally sound. For the FDM method, the microrotors have to be printed with the blade plane perpendicular to the print bed and the blades oriented such that the blades have the strongest structural layout possible. For four and two blades, the best configurations are having the blades at having the blades at 60° and 0° (horizontal) to the print bed respectively. The PJ method, is capable of printing highly accurate microrotors flat on the print bed. However, they are less stiff and tend to flap more and structurally deform under exposure to ultraviolet (UV) and heat sources, hence making them more suitable for short term usage. Test results indicate that the FDM rotors produce more thrust than PJ rotors and have a lower torque-to-thrust ratio due to the fact that PJ rotors are less stiff. This in turn leads to excessive flapping and more susceptibility to flutter, which requires thicker blades at the expense of higher profile drag. Likewise, PJ rotors can be designed for higher thrust and lower torque-to-thrust ratio by incorporating constant chord blades at lower pitch angles, yet maintaining the same diameter and solidity as their variable chord counterparts.