Viability and Validation of Near-Passive Descent Control for Quadrotor Systems

Abstract

A quadrotor unmanned aerial vehicle capable of lifting small payloads can be used to deliver small payloads from high altitudes rapidly and with high accuracy. This thesis explores the viability of three methods for delivering a quadrotor capable of lifting small payloads using near-passive means for control from high altitudes without the use of additional decelerators such as parachutes. All three methods utilize a variation of autorotation during descent to reduce the amount of energy consumed. The first method uses variable-pitch rotor blades to control the quadrotor's attitude during descent. This is shown by using a proportional-integral-derivative controller to stabilize a one degree-of-freedom variable-pitch balance in a custom wind tunnel section. A 6 degree-of-freedom variable-pitch quadrotor is designed and deployed from altitude during flight testing. The motors were unable to change directions while the quadrotor was descending. The next near-passive descent method explored makes use of motor controllers and motors capable of driving the quadrotor's rotor blades bidirectionally. Bench testing shows the quadrotor can stabilize and accurately track step inputs with the rotors spinning backwards and the throttle reduced. The bench testing results were not replicated during flight testing. The third method uses a typical quadrotor controlled by custom flight software that allows the quadrotor to perform half flips. The quadrotor is capable of inverting itself and flying towards the ground while maintaining control with reduced throttle. Bench testing shows the quadrotor is easily able to track step inputs with reduced throttle. Flight testing shows the quadrotor is capable of gliding in a desired direction while descending. The best performing method is the inverted descent method.