Planetary gear transmission mechanism

A planetary gear transmission mechanism, comprising:

• an input shaft;
• an input bevel gear connected to the input shaft;
• at least one planetary bevel gear meshed with the input bevel gear;
• two central axles extending from opposite sides of the at least one planetary bevel gear;
• an output gear driven by the at least one planetary bevel gear, wherein the output gear defines at least one through hole along one axis, the at least one planetary bevel gear being received in the at least one through hole and rotatably connected to the output gear, the rotation axis of the at least one planetary bevel gear is substantially perpendicular to the rotation axis of the output gear, the rotation axis of the output gear is coaxial with the rotation axis of the input bevel gear;
• a stationary bevel gear meshed with the at least one planetary bevel gear, wherein the input bevel gear and the stationary bevel gear are positioned on opposite sides of the output gear;
• and
• at least one bearing module received in the at least one through hole of the output gear, the at least one bearing module rotatably supporting the at least one planetary bevel gear, wherein the at least one bearing module comprises two bearing seats positioned on opposite sides of the corresponding through hole of the output gear, two bearings respectively sleeved on the central axles and received in the bearing seats, and two bearing covers positioned on the bearing seats to cover the bearings.