Framework for comparing and optimizing of fully actuated multirotor UAVs

Multirotor UAVs (unmanned aerial vehicles) have seen a great growth in popularity in the past years. However the application of these UAVs has been limited to simple flying tasks. For these tasks the optimal UAV design is very straightforward: an in-plane rotor configuration with parallel rotors. Although this design is inherently underactuated, it is able to fly in all required directions by tilting itself towards the desired direction. The application of multirotor UAVs could be expanded when full actuation of the six degree’s of freedom (DoFs) could be achieved by the UAV. These applications include: object manipulation, assembly, contact inspection tasks, etcetera. To achieve full actuation, the UAV needs to be able to produce thrust in all directions and the thrust generated by only parallel rotors will no longer suffice. The optimal rotor configuration is no longer straightforward, but depends on the requirements of the application. In order to find the optimal rotor configuration for any application, a framework is presented that compares available fully actuated UAV concepts with a set of qualitative criteria, such as: design complexity and flying stability, as well as a set of quantitative criteria that compare the wrench and accelerations of the concepts. These criteria are general and are used to evaluate the strengths and weaknesses of a number of concepts found in literature. In this way the framework can be applied for any application, as a first step to determine the optimal rotor configuration. To demonstrate the usability of the framework, two UAVs have been developed for two different applications that require full actuation. The first application is a large crop spraying UAV. Due to the great width and low flying height, this UAV can only roll very little before colliding with the ground. To be able to withstand side-wind disturbance, this UAV needs to be able to translate in sideways direction without changing orientation, so horizontal actuation is required. The optimization of this UAV yielded a UAV with optimized rotor positions and a number of rotor tilt configurations that can be applied for different wind speeds. This optimization shows how the framework can be used to create a multirotor design with very specific requirements and limitations. The second application is a human interacting UAV. This UAV needs to be omnidirectional to response to any wrench applied to it by humans. The optimization of the rotor configuration of this UAV has been done for six, eight and ten rotors, using a scalar measure for the entire achievable acceleration called the dynamic manoeuvrability. The optimization yielded a number of solutions for coupled and decoupled dynamic manoeuvrability, as well as a solution with high thrust efficiency. These solutions have been compared extensively, resulting in a UAV with high flying efficiency and high omnidirectional accelerations, as well as a better insight in the applicability of dynamic manoeuvrability in the optimization of UAVs. The optimization for the crop spraying UAV and the the human interacting UAV shows that the framework can be applied for a wide range of applications.