Abstract
A quadcopter is an Unmanned Aerial Vehicle (UAV) with 4 propellers providing required force for motion. It has four equally spaced rotors, typically arranged at the corners of a central body. With four independent rotors, the need for a swashplate mechanism like that in a regular helicopter is alleviated. Due to the rotation of the propellers attached to a quadcopter an upward thrust is generated. The maneuverability of a quadcopter is primarily controlled by adjusting the speed of each propeller attached to a rotor which in turn creates different lifting forces for maneuvering. The objective of this work is to design a 2-axes rotation mechanism for a shaft while its propeller rotates about its own (the 3rd) axis in a 1 m by 1 m quadcopter. Besides the spinning of a propeller axis, two other perpendicular axes in the mechanism are capable of pivoting in a flight which dynamically modifies the thrust vector direction and enhances the quadcopter’s maneuverability. The project was accomplished by performing several key tasks involving mechanism design using bevel gears, shafts, and motors, computational fluid dynamics analysis to determine aerodynamic thrusts and airflow pattern, rigid body dynamics analysis to evaluate forces and torques at different sections of the mechanism, and finite element analysis of mechanical components to optimize the stresses and fatigue as well as their corresponding safety factors. The final mechanism design provides mobility similar to a spherical joint capable of pivoting from −45 degrees to 45 degrees about 2 orthogonal axes for a small size drone. The results of rigid body dynamics analyses for a small size drone indicate that the minimum required motor torque is about 0.5 N-m, based on using a 40-mm driving nylon gear with gear ratio of 1:2 and an aluminum shaft with its propeller rotating at 2000 rad/sec, the nylon gear is good for 5 million cycles, the ABS plastic fixture is good for 10 million cycles and the shaft was designed for 1 billion cycles of fatigue life. Further study would be required in developing the control system for this quadcopter design and optimizing the entire structure of the drone, prototype verification of the mechanism design on flight maneuverability is also recommended. A parallel study using the layered composite design is currently undertaken. A comparison between metal and fiber composite shafts on weight reduction and performance of the mechanism would be revealed in our next paper.
Slipping–rolling transitions of a body with two contact points
