Micro aerial vehicles (MAVs) have gained increasing popularity thanks to their po- tential applications. Among them, different platforms feature unique advantages and drawbacks. Prevalently adopted multirotor vehicles enjoy a simple mechanical design with precise, agile, and highly versatile flight abilities. However, miniatur- ization adversely affects power efficiency. Small multirotor vehicles grossly suffer from energetic deficiencies because of the use of compact propellers and their flight times shorten to minutes. In contrast, fixed-wing aircraft demonstrate better aero- dynamic efficiency thanks to the use of large aerodynamic surfaces. Nevertheless, their inability to hover severely limits the versatility.

To work around the limitations, in this thesis, we report an alternative approach to fly, revolving flight. To elaborate, in flight, the entire body of the robot keeps revolving at a particular angular velocity. Under the different configurations, these revolving aerial vehicles show different dynamic properties and advantages in appli- cations. By analyzing the special aerodynamics and dynamics, we proposed three novel revolving robots including (i) a winged revolving robot that is able to hover with boosted power efficiency, (ii) a bi-modal aerial robot that is able to both ef- ficient hover and forward flight, and (iii) a combinable quadcopter that is able to split into two revolving bicopters midair.

Firstly, the efficient hovering is achieved by mimicking autorotating winged seeds, leveraging pronounced aerodynamic surfaces and delayed stalls for lift generation. The proposed vehicle possesses two opposite-placed flat wings and two motor-driven propellers. In hovering, the two propellers drive the entire robot to revolve mid-air. The revolving wings generate lift to keep the robot aloft. Blade-element momentum theory is employed to minimize power consumption. As a result, the 42.8-gram robot demonstrates a two-fold decrease in power consumption compared to other vehicles with similar weights. Employing power loading as the merit to evaluate the power efficiency, the robot displays the power loading of 8 grams per watt. This results the endurance of 24 mins.

Secondly, we combined the revolving-wing robot with a conventional aircraft robot to achieve the bi-modal locomotion. To enable the vehicle to transform between flight modes, a thrust-induced transformation mechanism is proposed. The mechanism features a variable-sweep mechanism and a span-wise wing rotational mechanism. By rotating the propeller-attached wing on one side, the revolving-wing robot trans- forms into an airplane. In forward flight, by altering the magnitudes of the thrust of propellers, the robot passively sweeps its wings to relocate the aerodynamics center of pressure to gain enhanced pitch maneuverability. Under certain flight maneuvers and associated wing loads, the robot is capable of switching back to the revolving- wing configuration mid-air. The ability to transform immensely extends the field of applications.

Lastly, we developed a revolving rotorcraft-bicopter. The flight dynamics of the proposed bicopter is significantly different from that of a regular multirotor vehicle. This includes the gyroscopic effect caused by the revolving motion and the underactuation. Despite this, model-based flight control strategies have been devised to enable the robot to fly and track a prescribed trajectory. Utilizing the controllable bicopter platform, we developed a novel quadcopter-splitflyer which is able to split and switch the flight mode midair.

To sum up, the scientific contributions of the work include but are not limited to (i) the framework for engineering a highly efficient revolving-wing aerial vehicle capable of hovering; (ii) flight control strategies for winged and unwinged revolving aerial vehicles and (iii) passive transformation mechanisms that allow the robot to transform between two flight modes in midair.