| Summary: | Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008. === This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. === Includes bibliographical references (p. 321). === On October 4th 2005, DARPA released a request for proposals for a Nano-Air Vehicle (NAV) program. The program sought to develop an advanced urban reconnaissance vehicle. According the requirement imposed by DARPA, the NAV was to have dimensions smaller than 7.5 cm in diameter, and a weight of approximately 10 grams, to allow indoor operation. On top of these requirements, this vehicle was to operate for about 20 minutes, and have a low noise signature to avoid risk of detection. This thesis addresses the propulsion system required to enable the DARPA NAV. In particular, a rotary-wing vehicle is favored because of its high efficiency and simplicity. One large challenge faced for this design is the torque canceling mechanism to counter the torque produced by the rotating rotor. To provide a reasonable torque canceling, the solution proposed here is to use a rotating motor inside the vehicle. One rotor will be attached to the shaft of the motor and the other to a motor body that is left free to rotate inside the vehicle. By letting the motor rotate freely inside the body, the torque is cancelled automatically without a gearbox. In addition to this passive torque canceling mechanism, a novel approach is used in the fabrication approach of the motor in order to maximize the power density of this propulsion system. This new fabrication method involves the use of flexible printed circuit for the stator of the motor, which allows for the motor to achieve high power density, while simplifying its manufacturing process. The main goal of this project is to combine these two novel approaches in order to design, fabricate and assess the performance of the proposed propulsion system design. In this thesis, a prototype propulsion system for this vehicle, featuring the new motor fabrication approach, is designed, fabricated and tested. === (cont.) Firstly, the design model required to design the main components of the propulsion system (the motor model, the propeller model, and the design optimization program) is developed. The fabrication process of the propulsion system is then established, and an operational propulsion system prototype is fabricated using the established design tools and fabrication procedure. Finally, series of experiments are conducted in order to characterize the performance of the propulsion system and to validate the model used in the design of the propulsion system. Based on the results obtained from the experiment, it is found that the motor model used in the design of the motor for the propulsion system is accurate, with an error of 5% in the prediction of output shaft power of the motor. Among various configuration tested for the propulsion system, a combination of 5-bladed propeller and 3-bladed propeller, designed around the motor operating speed of 9,000 rpm is found to be most optimal for this propulsion system, featuring the following performance:for maximum achievable thrust of 17.28 g, well beyond hover thrust required for the vehicle;for capable of providing hover thrust at a power consumption of 1.26W, which translates to an hovering endurance of approximately 20 minutes using a lithyum polymer battery chosen for the vehicle;for torque cancelling mechanism capable of cancelling up to 99% of torque generated in the motor; and for noise footprint lower than 45 dBA, a typical indoor background noise during the day, 1 m away from the propulsion system. Based on these results, it is concluded that the propulsion system developed here is capable of meeting all the requirement imposed by DARPA. Since this research does not focus on the control aspect of the vehicle, further research should be conducted in the field of control and navigation in order to achieve a fully autonomous NAV. === by Sho Sato. === S.M.
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