Unmanned aerial vehicle

An unmanned aerial vehicle (UAV) comprising:

• a housing;
• a wireless communication circuit positioned inside or connected to the housing, wherein the wireless communication circuit is configured to establish wireless communication with an external controller;
• a plurality of propulsion systems connected to or at least partially embedded in the housing;
• and
• a navigation circuit configured to control the propulsion systems,
• wherein at least one of the plurality of propulsion systems includes:
• a motor controlled by the navigation circuit;
• a rotation shaft having an axis extending in a first direction, and including a first end and a second end, wherein the first end is connected to the motor, and wherein the rotation shaft is configured to be rotated in a first rotational direction by the motor;
• a cap structure fixed to the second end of the rotation shaft;
• and
• a propeller including:
• a hub including a through-hole formed in the first direction, such that the rotation shaft rotatably passes through the through-hole;
• and
• a plurality of blades connected to the hub in second directions substantially perpendicular to the first direction,
• wherein the propeller is detachably fixed to or connected to the cap structure, such that, when an external force is exerted on at least one of the blades, the propeller is released from the cap structure to be freely movable along the axis toward the motor,
• wherein the cap structure includes a surface facing toward the propeller, and at least one spiral recess formed in the surface,
• wherein the hub includes at least one protrusion slidably engaged in the at least one spiral recess when the propeller is connected to the cap structure,
• wherein at least one of the propulsion systems includes a coupling structure configured to apply a predetermined force to the propeller in the first direction such that the propeller is not separated from the cap structure, and
• wherein the coupling structure is composed of a surface, which faces the propeller, of the cap structure, magnets disposed on the surface, and metallic portions disposed at positions corresponding to the magnets on the hub.