Logical cube - 4x4x4
This 4x4x4 logical cube is a more daunting challenge than the 3x3x3 cube. The number of pieces is far greater, and there are no "fixed" pieces to serve as a reference.
The puzzle has an ingenious mechanism. The sphere has eight perpendicular grooves, aligned two by two, for the center tiles to slide in. A specially shaped steel frame prevents the sphere from becoming misaligned with the rest of the cube. There are two edge pieces at each face intersection.
Patent no. RO 106960 B1 / 1993-08-30