A rotor assembly comprising a rotor for rotating in a magnetic field of a motor, the rotor comprising a main rotor cavity and a plurality of first holes; two side boards, each side board comprising a sleeve-shaped main side board body and a disc-shaped outer side board body, the side board body having a main side board cavity, and the outer side board body being perforated by a plurality of second holes; two damping elements each damping element comprising a main damping element cavity; a plurality of rubber sleeves, each rubber sleeve having a rubber sleeve lip; and a plurality of third holes; an axle; and a plurality of positioning pins.