Okay, here's an illustration of why it's hard to get back where you started.
Gear Up has four
moving layers, but each layer is made of two
thicknesses of acrylic sheet, so it looks a bit like an 8-layer puzzle.Start:
To verify when the puzzle is solved, the protruding tabs have notches on them. When the puzzle is perfectly solved you can look through all eight layers of acrylic like this...
File comment: When solved, the grooves line up.
Gear02.jpg [ 61.78 KiB | Viewed 1291 times ]
Holding the bottom two layers together, I turn the first layer anticlockwise. The second layer slowly follows. Due to the gearing, all movements require at least this much freedom. The layers must move in groups of three or four, never just one or two.
File comment: Separating the first three layers.
Gear03.jpg [ 92.98 KiB | Viewed 1293 times ]
While holding the first and fourth layers steady, I push the third layer away from the fourth layer. Notice how this propels the second layer past the first layer.
File comment: Push the third and fourth layers apart.
Gear04.JPG [ 88.2 KiB | Viewed 1292 times ]
Trying to go back:
When I try pushing the first three layers together again, the fourth layer spins away. The fourth layer can't move without pushing the other layers apart!
File comment: The fourth layer can't move without messing up the other three.
Gear05.JPG [ 91.92 KiB | Viewed 1289 times ]
There's no trick mechanism here, just sneaky psychology and efficient use of co-primes. It's hard to go back because the mechanism lures the user into doing the wrong thing. The intuitive pairing of the front-two layers or the back-two layers tempts the user into locking himself into irritating situations where all the gears seem to be "off-by-one" from being solvable.