Pancake motor

1. A gear motor comprising:

a housing;

an electric motor including an outer stator and a rotor surrounded and driven by the outer stator;

a planetary gear train including a plurality of planet gear assemblies, a stationary ring gear at one end of the planet gear assemblies, and a driving ring gear at the other end of the planet gear assemblies wherein the planet gear assemblies are positioned between the stationary ring gear and the driving ring gear, each planet gear assembly includes a first gear and a second gear coaxial with and co-rotated with the first gear, the first and second gears are disposed in a carrier, the first gear meshes the stationary ring gear, and the second gear meshes the driving ring gear;

a driving shaft rotatably disposed through the housing and secured to the driving ring gear as a power output;

wherein the rotor and the carrier are secured together to form an annular rotor having a central opening put on the driving shaft, two spaces are formed at two ends of the carrier respectively, each space being configured to receive either the stationary ring gear or the driving ring gear, the number of the teeth of the first gear is equal to that of the teeth of the second gear, the number of the teeth of the stationary ring gear is different from that of the teeth of the driving ring gear, and a difference between the number of the teeth of the stationary ring gear and that of the teeth of the driving ring gear is a multiple of the number of the planet gear assemblies; and

an annular plate for fastening the outer rotor and the carrier together, and wherein the spaces are disposed at two ends of both the annular plate and the carrier respectively.

2. The gear motor of claim 1 , wherein a difference between the number of the teeth of the stationary ring gear and the number of the teeth of the driving ring gear is equal to the number of the planet gear assemblies.

3. The gear motor of claim 1 , wherein the modulus of the first gear is different from the modulus of the second gear, the modulus of the stationary ring gear is equal to that of the first gear, and the modulus of the driving ring gear is equal to that of the second gear.

4. The gear motor of claim 1 , wherein the stationary ring gear is fastened in the housing.

5. The gear motor of claim 1 , further comprising first and second carrier discs disposed at two ends of the planet gear assemblies respectively, wherein the first and second carrier discs constrain the planet gear assembly in position, and wherein the first and second gears are configured to rotate about the driving shaft.

6. The gear motor of claim 5 , further comprising a plurality of axles each disposed through the first and second gears of each planet gear assembly, and wherein two ends of each axle engage the first and second carrier discs respectively.

7. The gear motor of claim 1 , further comprising a disc for attaching the driving ring gear to the driving shaft.

8. The gear motor of claim 1 , wherein the electric motor is a brushless direct current motor.

9. A gear motor comprising:

a housing having a first shell and a second shell, the second shell including a central opening and releasably secured to the first shell;

an electric motor disposed in the housing and including an outer stator and a rotor surrounded and driven by the outer stator;

a planetary gear train disposed in the housing and including a plurality of planet gear assemblies, a stationary ring gear at one end of the planet gear assemblies, and a driving ring gear at the other end of the planet gear assemblies wherein the planet gear assemblies are positioned between the stationary ring gear and the driving ring gear, each planet gear assembly includes a first gear and a second gear coaxial with and co-rotated with the first gear, the first and second gears are disposed in a carrier, the first gear meshes the stationary ring gear, and the second gear meshes the driving ring gear;

a power output secured to the driving ring gear, the power output rotatably disposed through the central opening of the second shell to be exposed on the housing;

a support cylinder disposed on a center of one surface of the first shell opposing the second shell, the support cylinder extending toward the second shell;

wherein the rotor and the carrier are secured together to form an annular rotor having a central opening put on the support cylinder, two spaces are formed at two ends of the carrier respectively, each space being configured to receive either the stationary ring gear or the driving ring gear, the number of the teeth of the first gear is equal to that of the teeth of the second gear, the number of the teeth of the stationary ring gear is different from that of the teeth of the driving ring gear, and a difference between the number of the teeth of the stationary ring gear and that of the teeth of the driving ring gear is a multiple of the number of the planet gear assemblies; and

an annular plate for fastening the outer rotor and the carrier together, and wherein the spaces are disposed at two ends of both the annular plate and the carrier respectively.

10. The gear motor of claim 9 , wherein a difference between the number of the teeth of the stationary ring gear and the number of the teeth of the driving ring gear is equal to the number of the planet gear assemblies.

11. The gear motor of claim 9 , wherein the modulus of the first gear is different from the modulus of the second gear, the modulus of the stationary ring gear is equal to that of the first gear, and the modulus of the driving ring gear is equal to that of the second gear.

12. The gear motor of claim 9 , wherein the stationary ring gear is fastened in the housing.

13. The gear motor of claim 9 , further comprising first and second carrier discs disposed at two ends of the planet gear assemblies respectively, wherein the first and second carrier discs constrain the planet gear assembly in position, and wherein the first and second gears are configured to rotate about the support cylinder.

14. The gear motor of claim 13 , further comprising a plurality of axles each disposed through the first and second gears of each planet gear assembly, and wherein two ends of each axle engage the first and second carrier discs respectively.

15. The gear motor of claim 9 , further comprising a disc as the power output.

16. The gear motor of claim 9 , further comprising a driving shaft through the disc, and wherein the driving shaft serves as a second power output.

17. The gear motor of claim 9 , wherein the electric motor is a brushless direct current motor.