Comparison of Fixed and Variable Pitch Actuators for Agile Quadrotors

This paper presents the design, analysis and experimental testing of a variablepitch quadrotor. A custom in-lab built quadrotor with on-board attitude stabilization is developed and tested. An analysis of the dynamic differences in thrust output between a fixed-pitch and variable-pitch propeller is given and validated with simulation and experimental results. It is shown that variable-pitch actuation has significant advantages over the conventional fixed-pitch configuration, including increased thrust rate of change, decreased control saturation, and the ability to quickly and efficiently reverse thrust. These advantages result in improved quadrotor tracking of linear and angular acceleration command inputs in both simulation and hardware testing. The benefits should enable more aggressive and aerobatic flying with the variable-pitch quadrotor than with standard fixed-pitch actuation, while retaining much of the mechanical simplicity and robustness of the fixed-pitch quadrotor. Nomenclature α Propeller pitch angle ω Motor speed ρ Air density bD1,...bD3 Estimated drag coefficients bL Estimated lift coefficient c Propeller cord R Motor internal resistance L Motor inductance CD0 Parasitic drag coefficient CDi Lift-induced drag coefficient CLα Lift coefficient CL0 Lift coefficient at zero pitch CLmin Minimum lift coefficient CLmax Maximum lift coefficient e Motor back EMF i Motor current i0 Motor no-load current I Motor and propeller inertia KV Motor voltage constant KQ Motor torque constant REexp Reynolds number adjusting factor Rp Propeller radius REref Reynolds number for drag calculations v Motor voltage vL Motor voltage from inductance TL Load torque vR Motor voltage from resistance TM Motor torque I.