Abstract
Multirotor is the umbrella term for the family of unmanned aircraft, which include the quadrotor, hexarotor and other vertical take-off and landing (VTOL) aircraft that employ multiple main rotors for lift and control. Development and testing of novel multirotor designs has been aided by the proliferation of 3D printing and inexpensive flight controllers and components. Different multirotor configurations exhibit specific strengths, while presenting unique challenges with regards to design and control. This article highlights the primary differences between three multirotor platforms: a quadrotor; a fully-actuated hexarotor; and an octorotor. Each platform is modelled and then controlled using non-linear dynamic inversion. The differences in dynamics, control and performance are then discussed.
Highlights
A multirotor is a rotorcraft, but differ from traditional helicopter configurations
This paper presents a comparison of three specific multirotor platforms: quadrotor, hexarotor and octorotor
Applications of the various platforms range from simple control investigation to state estimation to fault tolerant control strategies. While these investigations are indicative of those performed on the quadrotor, the literature highlights a lack of discussion on the differences of multirotor platforms with regards to such investigations
Summary
A multirotor is a rotorcraft, but differ from traditional helicopter configurations. Rather than employing mechanically-complex main and tail rotors, a multirotor employs several identical rotors to provide both lift and control. The primary benefit of this approach in the context of obtaining consistent system performance across a range of platforms is that it transforms a non-linear multiple-input multiple-output (MIMO) system into a series of linear single-input single-output (SISO) systems. The performances of these linear systems are specified through simple pole placement or, if desired, more complex control laws [2]. Taking the quadrotor as the baseline system, a discussion is presented on the changes to the vehicle dynamics, controller and closed-loop performance as a result of augmenting the aircraft with additional rotors. It is seen through simulation testing that the actuator limits in each system limit the ability of each system to exhibit identical performance
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