Energy sources such as batteries do not decrease in mass after consumption, unlike combustion-based fuels. We present the concept of staging energy sources, i.e. consuming energy in stages and ejecting used stages, to progressively reduce the mass of aerial vehicles in-flight which reduces power consumption, and consequently increases flight time. A flight time vs. energy storage mass analysis is presented to show the endurance benefit for multirotors on staging. We consider two specific problems in discrete staging -optimal order of staging given a certain number of energy sources, and optimal partitioning of a given energy storage mass budget into a given number of stages. We then derive results for two continuously staged cases -an internal combustion engine driving propellers, and a rocket engine. A fundamental flight time limit is seen for the internal combustion engine case, but not for the rocket engine, suggesting that rocket engines could be a better choice in certain scenarios. Lastly, we conduct flight experiments a on a custom two-stage battery-powered quadcopter. This quadcopter can eject a battery stage after consumption in-flight using a custom-designed mechanism, and continue hovering using the next stage. The experimental flight times are compared with those predicted from the analysis for our vehicle. The values match well which validates the presented staging analysis.
In this article, a novel quadcopter capable of changing shape midflight is presented, allowing for operation in four configurations with the capability of sustained hover in three. This is accomplished without requiring actuators beyond the four motors typical of a quadcopter. Morphing is achieved through freely rotating hinges that allow the vehicle arms to fold downwards by either reducing or reversing thrust forces. Constraints placed on the control inputs of the vehicle prevent the arms from folding or unfolding unexpectedly. This allows for the use of existing quadcopter controllers and trajectory generation algorithms with only minimal added complexity. For our experimental vehicle at hover, we find that these constraints result in a 36% reduction of the maximum yaw torque the vehicle can produce, but do not result in a reduction of the maximum thrust or roll and pitch torques. Experimental results show that, for a typical maneuver, the added limits have a negligible effect on the trajectory tracking performance. Finally, the ability to change configurations is shown to enable the vehicle to traverse small passages, perch on hanging wires, and perform limited grasping tasks.
This paper presents the design and control of a novel quadcopter capable of changing shape mid-flight, allowing for operation in four configurations with the capability of sustained hover in three. The normally rigid connections between the arms of the quadcopter and the central body are replaced by free-rotating hinges that allow the arms to fold downward; no additional actuators beyond the four motors that drive the propellers are used. Configuration transitions are accomplished by either reducing or reversing the thrust forces produced by specific propellers during flight. Constraints placed on the control inputs of the vehicle prevent the arms from folding or unfolding unexpectedly, allowing for the use of existing quadcopter controllers and trajectory generation algorithms. For our experimental vehicle at hover, we find that these constraints result in a 36% reduction of the maximum yaw torque the vehicle can produce, but do not result in a reduction of the maximum thrust or roll and pitch torques. Furthermore, the ability to change configurations is shown to enable the vehicle to traverse small passages, perch on hanging wires, and perform simple grasping tasks.
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