Design and control of a spherical VTOL vehicle

Abstract

This research presents the design of a spherically shaped Unmanned Aircraft System (UAS) called the All-Terrain Land and Air Sphere (ATLAS). ATLAS is designed to include competing design requirements necessary for operating in an indoor cluttered environment for emergency response and inspection applications, particularly around people, including the ability to hover, execute coordinated maneuvers with translational flight, land on uneven terrain, and return to flight. The spherical frame can interact with the environment and land without the need for coordinated vertical landing maneuverability such as other rotary winged devices, including multi-rotors or helicopters. One of the features that sets ATLAS apart from other similarly sized drones is the capability to roll on the ground to maneuver to a new location and avoid obstacles before executing an upright maneuver for recovery to flight. These features make ATLAS suitable as a search and rescue platform in supporting both aerial and ground operations. The diameter and payload capability of the ATLAS is scalable depending on the mission requirements. While multiple sizes have been developed, the primary system presented herein has a diameter of 40 cm (16 inch) and weighs about 900 grams (2 lbs).

The first part of this study investigates the characteristic of a passive flight control mechanism made up of eight movable hinged arc vanes positioned radially around the propeller tips. Such passive devices are not presented in any open propeller platform. Each vane is hinged and mechanically restricted to rotate between 0 to 90 degrees. A series of bench testing results show that these passive control surfaces generate an upward or downward force depending on the proximity and strength of the airflow interaction coming toward the propeller during flight conditions. These passive vanes can also help stabilize the vehicle in contrast to an open propeller setup.

The second part of this study evaluates control schemes for a single propeller with multiple control surfaces. Unlike ducted fans and multi-rotor platforms, the control vanes are strongly coupled to provide stability and control along all principal axes while counteracting the induced torque effects generated by a single pitch propeller. ATLAS has demonstrated stable flight tests by using a Proportional-Integrator-Derivative (PID) control based on the proposed control scheme and can successfully perform flight recovery from in-flight disturbances through the implementation of a non-linear model using the Newton-Euler formulation. Ground maneuvers are made possible by reversing the propeller direction to provide sufficient reverse thrust without the need for a variable pitch propeller.