Omni-directional wheel

1. An omni-directional wheel comprising:

a hub rotatable about a wheel axis;

a first row of angled rollers about the hub each rotatably supported by the hub; and

at least a second row of angled rollers about the hub each rotatably supported by the hub, the second row of rollers axially offset along the wheel axis from the first row and rotationally offset from the first row about the wheel axis, wherein the rollers of the second row are not coaxial with the rollers of the first row.

2. The omni-directional wheel of claim 1 , wherein the rotational offset between rows of angled rollers is defined by the quotient 360/(n×r) degrees, where n is the total number of angled rollers per row and r is the total number of rows of angled rollers.

3. The omni-directional wheel of claim 2 , wherein the rollers of any one row do not form a substantially complete circle when viewed along the wheel axis, but the rollers of additional rows fill in the angular gaps between rollers resulting in a substantially round wheel.

4. The omni-directional wheel of claim 2 , wherein n is between 3 and 7.

5. The omni-directional wheel of claim 2 , wherein r is greater than 2.

6. The omni-directional wheel of claim 1 , wherein the angled rollers all have a common roller angle, wherein the common roller angle is defined as the angle between a plane perpendicular to an axis of the respective roller and a plane perpendicular to the wheel axis.

7. The omni-directional wheel of claim 6 , wherein the roller angle is between 35° and 55°.

8. The omni-directional wheel of claim 6 , wherein the roller angle is less than 35°.

9. The omni-directional wheel of claim 1 , wherein each roller is supported on both its ends by the hub.

10. The omni-directional wheel of claim 9 , wherein there are two rows of rollers and the hub includes a center rim sandwiched by and attached to an inner flange and an outer flange, wherein the rollers of the first row are mounted between the center rim and the inner flange, and the rollers of the second row are mounted between the center rim and the outer flange.

11. The omni-directional wheel of claim 1 , wherein each roller is supported on only one end by the hub.

12. The omni-directional wheel of claim 11 , wherein there are two rows of rollers and the hub includes a zig-zag center rib and the rollers of one row are disposed on one side of the zig-zag center rib and the rollers of the other row are disposed on the other side of the zig-zag center rib.

13. The omni-directional wheel of claim 1 , wherein the rollers of one of the rows are nested with the rollers of an adjacent row such that the rollers of both rows intersect a common plane orthogonal to the wheel axis.

14. The omni-directional wheel of claim 1 , further comprising redundant rows of rollers to provide a minimum of two rollers for contact with a flat surface parallel to the wheel axis.

15. The omni-directional wheel of claim 1 , wherein the ends of each roller all have a substantially equal diameter.

16. An omni-directional vehicle having at least three omni-directional wheels each comprising:

a hub rotatable about a wheel axis;

a first row of angled rollers about the hub each rotatably supported by the hub; and

at least a second row of angled rollers about the hub each rotatably supported by the hub, the second row of rollers axially offset along the wheel axis from the first row and rotationally offset from the first row about the wheel axis,

wherein the rollers of the second row are not coaxial with the rollers of the first row, and the rollers of both rows have a substantially common roller angle, wherein the roller angle is defined as the angle between a plane perpendicular to an axis of the respective roller and a plane perpendicular to the wheel axis.

17. The omni-directional vehicle of claim 16 , wherein the omni-directional vehicle has four of said omni-directional wheels.

18. The omni-directional vehicle of claim 17 wherein:

the vehicle is elongated and has a long axis; and

the wheels are oriented with their axes aligned within 15° of the long axis of the vehicle.

19. The omni-directional vehicle of claim 18 , wherein the diameter of each wheel is smaller than the width of said wheel.

20. The omni-directional vehicle of claim 17 , further including a chassis and a suspension system allowing independent vertical motion of each of the omni-directional wheels with respect to the chassis while keeping the wheel axes of the wheels approximately parallel to the driving surface.

21. The omni-directional vehicle of claim 20 , wherein the suspension system is actively controlled and can raise or lower the chassis.

22. The omni-directional vehicle of claim 21 , wherein the load can be reduced on one diagonally opposed pair of the omni-directional wheels while increasing the load on the other diagonally opposed pair of diagonally opposed the omni-directional wheels.

23. The omni-directional vehicle of claim 22 , wherein the suspension system actively controls the pitch or roll angle of the chassis relative to the driving surface.

24. The omni-directional vehicle of claim 17 , wherein the roller angle of each wheel is between 35° and 55°, one diagonally opposed pair of the omni-directional wheels are right-handed, and the other diagonally opposed pair of the omni-directional wheels are left-handed.

25. The omni-directional vehicle of claim 17 , wherein the roller angle of each wheel is less than 40°, all four wheels have the same handedness, the wheel axes of diagonal opposing ones of the omni-directional wheels are within 15° of parallel, and the wheel axes of adjacent ones of the omni-directional wheels are within 15° of perpendicular.