US Patent 10035581 Multi-rotor UAV with compact folding rotor arms

A multi-rotor UAV comprises a body and a plurality of rotor arms extending radially from the body. A rotor assembly is connected to an outside end of each rotor arm. An attachment interface is connected to the body and provides rotor arm attachment points for attaching the rotor arms to the body and pivoting the rotor arms from an unfolded operating position, to a folded position wherein the rotor arms are pivoted such that an outer arm portion of each rotor arm is enabled to cross the pivot end and an inner arm portion of an adjacent rotor arm.