About

Rubik's Shells is a puzzle that consists of 4 intersecting rings, coloured wheels with 8 balls each, which can rotate. The wheels are in two pairs; two axes with a pair of wheels on each, and the two axes are separated and at right angles to each other so that any wheels from one axis has exactly one ball in common with any wheel from the other axis. The object of the puzzle is to separate the coloured balls, each colour into its own wheel. There are 28 balls, 7 of each colour. There are 4 intersections, so 4 balls will belong to two wheels simultaneously. Each wheel intersects two others, so in the solved state each wheel will have one intersection of its own colour, and the ball at the other intersection matches that of the other wheel. An interesting feature of this puzzle is that each axis also has a button. By pressing a button, the two wheels on that axis permanently lock together. There are therefore 3 grades of difficulty; Basic (no buttons pressed), Tough (one button pressed), and Challenge (both buttons pressed). Note that once pressed, the buttons can never be released (unless you drill a hole in the button and use a hook or screw to pull it back out). Also, the puzzle is always solvable, even if the buttons are pressed when it is in a mixed state. Pressing a button takes some force, so there is no danger of doing so accidentally. The number of positions: There are 28 balls, which can be arranged in at most 28! ways. This limit is not reached because they fall into 4 groups of 7 indistinguishable balls. This means the number of positions is 28!/ 7!4 = 472,518,347,558,400. It should also be mentioned that there are actually two solutions, because the balls at the intersections can be arranged in two ways. The booklet that comes with the puzzle has picture diagrams that show various puzzle positions. These diagrams show the balls in a cross, as if the rings were cut open. The two solved positions are shown in the following diagrams. I have added the letters b, g, w, r to indicate the 4 colours, so it remains legible when the page is printed. w b w b w b g g g w g g g g r r r r b r r r w b w b w b w b w b w b g g g g b g g g r r r w r r r r w b w b w b If your browser supports JavaScript, then you can play Rubik's Shells by clicking the link below: