An unmanned vehicle includes a vehicle body and at least one arm assembly. The arm assembly is coupled to the vehicle body. The arm assembly includes a first rotating member, a second rotating member, and a propeller. The second rotating member is coupled to the first rotating member. The propeller includes a propeller rim encircling an outer edge of the propeller and a rotatable axle coupled to the second rotating member. The the rotatable axle extends along a rotating axis. The second rotating member is configured to turn the propeller by rotating the rotatable axle about the rotating axis. The first rotating member is configured to rotate and effect a movement of the second rotating member so as to selectively adjust the rotatable axle to align the rotating axis at least with a first axial direction and a second axial direction.