Analysis and Control of a Variable Pitch Quadrotor for Agile Flight

Abstract

Fixedpitch quadrotors are popular research and hobby platforms largely due to their mechanical simplicity relative to other hovering aircraft. This simplicity, however, places fundamental limits on the achievable actuator bandwidth and the possible flight maneuvers. This paper shows that many of these limitations can be overcome by utilizing variablepitch propellers on a quadrotor. A detailed analysis of the potential benefits of variablepitch propellers over fixedpitch propellers for a quadrotor is presented. This analysis is supported with experimental testing to show that variablepitch propellers, in addition to allowing for generation of reverse thrust, substantially increase the maximum rate of thrust change. A nonlinear, quaternionbased control algorithm for controlling the quadrotor is also presented with an accompanying trajectory generation method that finds polynomial minimumtime paths based on actuator saturation levels. The control law and trajectory generation algorithms are implemented on a custom variablepitch quadrotor. Several flight tests are shown, which highlight the benefits of a variablepitch quadrotor over a standard fixedpitch quadrotor for performing aggressive and aerobatic maneuvers.