Text

theses

ETD doctoral

Micro Aerial Vehicles (MAVs) are increasing in popularity and are finding applications in both the civil and defense sectors. A major limitation of MAV plat- forms is low endurance, which greatly diminishes mission capabilities. This study was restricted to MAVs with a characteristic length of 20cm or less and a weight of less than 100 grams; although, these restrictions were relaxed in a few cases. A comprehensive approach was taken to develop a high endurance coaxial MAV. A literature review showed that hover capable organisms, such as hummingbirds and bats, also suffer from the same low aerodynamic efficiency issues that MAV designers face. Following nature’s example, the maximum possible power loading, also known as hover efficiency, was increased by minimizing vehicle disc loading. Through simulations and experiments, the classic quadcopter platform proved too inefficient to achieve maximum endurance. Higher aerodynamic efficiencies did not provide a high enough power loading to achieve high endurance. This investigation shows that the coaxial configuration, due to it’s very low disc loading, has the highest power loading and therefore the highest possible endurance. Mo- tor/propeller matching was also performed to maximize efficiency. A database of propellers and motors was created and all possible combinations were simulated, along with different gear ratios, to shift the motor efficiency peak closer to that of the propeller. This optimization yielded a propulsion system which had a power loading comparable to biological flyers. Finally, the entire vehicle was simulated using a battery optimization model and accurate predictions of vehicle weight, thrust and endurance were obtained. Using this approach, hundreds of vehicle and component combinations can be simulated and optimized rapidly. The developed model included simulations for the static hover case and a dynamic case, where a constant climb rate was considered. Dynamic case simulations predicted the optimal climb rate to achieve maximum altitude. Using precomputed data obtained from the simulations, a Pareto front was created and an optimal vehicle configuration was selected. This approach was used to create a coaxial micro drone with a maximum achieved endurance of 37 minutes. This endurance represents a 460% improvement over the average 8 minute flight time of the sub 100g drones examined. The simulations and models developed in this study resulted in predicted MAV endurances within 30 seconds of the experimental measurements, regardless of payload or battery size. Total flight weight ranges were between 40 and 88 grams depending on payload and the MAV version in question. The final MAV platform created was foldable into a 40mm profile and launchable via a pneumatic launching device. Basic air/water capabilities were also demonstrated giving the MAV the ability to be deployed from underwater. Future work includes adding robust autonomy and swarming capabilities.

ETD_11229

Ph.D.

Includes bibliographical references

doi:10.7282/t3-61b9-v346

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