Thursday, March 22, 2012

Clingstone-Freestone: Triumph & Disaster

Clingstone-Freestone came to me in a flash of inspiration, a fully-formed idea for a puzzle that could be built to resemble a ripe peach with a wedge cut out to expose the stone.  It seemed like a nice idea, but would it work?  Yes, it worked on the first try...but no it didn't turn out a good puzzle.
The premise?  The inner sphere must be correctly positioned to allow two halves of the outer sphere to move freely.  Then the two halves would un-hinge to rotate apart around an axis located un-intuitively at an imaginary point on the missing 'slice' of the outer sphere.
The inner 'stone' is a sphere divided into 3 pieces: one smaller piece with two-axis mirror symmetry, and two congruent larger pieces whose outlines look like continuations of some curves of the smaller piece.
But inside, the larger pieces exhibit two distinct bisecting geometries: a revolution around an imaginary point in the upper half, and a helical slice through the lower half.  The cuts are arranged so the outlines meet seamlessly on the outside of the sphere, thereby disguising the internals.
When the cavity is empty, the outer shell be put together and taken apart without any interference.  But if the 'stone' is installed, the parting lines block it from being disassembled in the same style a Bram Cohen's Cast Marble or Vesa Timonen's Tangerine puzzle.
Only a small part of the 'stone' is visible at any given time, so it takes a lot of maneuvering just to figure out the outlines of the cuts...let alone guess at the internal shapes.
Even after the user guesses the shape and orients the 'stone' correctly, it's still a bit unintuitive to open the puzzle because it unhinges around an axis outside the surface of the puzzle.  It won't disassemble unless the user gets the right motion.
Another unintuitive detail, the disassembled puzzle is very asymmetrical.  The smaller piece of the stone comes out with one of the halves, while the two identical pieces remain cradled inside the other half.

So far, the mechanism seemed to work perfectly on the first (and only) prototype I built.  But the whole premise has an intrinsic flaw....
In some orientations of the stone, there would be nothing to prevent the smaller piece from being extracted through the opening.
Removing the smaller piece not only permits the user to see the inner workings of the puzzle, it partly-resolves the obstruction.  Although it's still somewhat challenging, it doesn't work as I'd intended.

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