My family have been having fun with the Turing Tumble. Thanks for creating this fascinating (and well designed) device.
A few times when we were trying free-form experimentation we wished that there was a piece that was the opposite of the crossover. If a ball came in from the left, it would exit to the left, and similarly for the right side. This would allow some designs that could be done with the current pieces but might be too large to fit on the board. Did you ever consider such a piece?