Some KO companies have produced them according to the patents, (Ex. 4x4) and these are inferior to V-Cubes products.
The use of less spherical shells helps the mechanism to be shallower, and the large spherical segments at the base of the corners and edges can stabilize the puzzle, much like a ball core does.
File comment: the virtual ball core
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7x7 pieces forming ball-like core
File comment: the ball core
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3x3 with a stabilizing ball core
One more V-Cube patent improvement
File comment: This shows a cylindrical inner surface, but the V-2 has a spherical inner surface, and an excellent bandaging method.
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These changes to the 2x2 prevent it from popping as much, since my V-2 still works with 2 opposite screws removed. (try it for yourself) This is because the other 4 surrounding centers have to move outward as well to pull off one layer of the cube.