Delivery drones used by logistics companies today are equipped with unshielded propellers, which represent a major hurdle for in-hand parcel delivery. The exposed propeller blades are hazardous to unsuspecting bystanders, pets, and untrained users. One solution to provide safety is to enclose a drone with an all-encompassing protective cage. However, the structures of existing cage designs have low density in order to minimize obstruction of propeller airflow, so as to not decrease efficiency. The relatively large openings in the cage do not protect hands and fingers from fast rotating propellers. Here we describe a novel approach to safety and aerodynamic efficiency by means of a high-density cage and morphing arms loosely inspired by the box turtle. The drone cage is made of a dense and lightweight grid. When flying in proximity of humans, the arms and propellers are retracted and fully sealed within the cage, thus making the drone safe and also reducing the total footprint. When flying at cruising altitude far from people and objects, the arms and propellers extend out of the protective grid, thus increasing aerodynamic efficiency by more than 20%.

中文翻译：

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一种变形货运无人机，可在人类附近安全飞行

如今，物流公司使用的送货无人机配备了无屏蔽螺旋桨，这是手头包裹递送的主要障碍。暴露的螺旋桨叶片对毫无戒心的旁观者、宠物和未受过训练的用户来说是危险的。提供安全性的一种解决方案是将无人机与无所不包的保护笼一起封闭。然而，现有笼子设计的结构密度较低，以尽量减少对螺旋桨气流的阻碍，从而不降低效率。笼子中相对较大的开口不能保护手和手指免受快速旋转的螺旋桨的伤害。在这里，我们描述了一种通过高密度笼子和受箱龟启发而变形的手臂来提高安全性和空气动力学效率的新方法。无人机笼由密集而轻巧的网格制成。在接近人类飞行时，臂和螺旋桨缩回并完全密封在笼子内，从而使无人机安全并减少总占地面积。在远离人和物体的巡航高度飞行时，臂和螺旋桨伸出防护网，从而使空气动力效率提高20%以上。