The Face Turning Octahedron in its solved state shown from the topA DianSheng Face Turning Octahedron, an example of newer hardware
The Face Turning Octahedron (often abbreviated as FTO) is a combination and mechanical puzzle. Unlike cubic puzzles, the FTO is based on an octahedral geometry with eight triangular faces that rotate independently. Its deep-cut mechanism and interplay of the various piece types give the puzzle a distinctive solving approach compared to other cubic puzzles.[1] The FTO is notable for being the first octahedral twisty puzzle to feature straight cuts, setting it apart from earlier octahedral designs.
History
The idea for the FTO was initially developed through a series of early patent filings. On February 9, 1982, Clarence W. Hewlett Jr. filed the first patent for a face-turning octahedron,[2] and just two weeks later, on February 24, 1982, Karl Rohrbach filed a similar patent.[3] However, neither patent led to a commercial product which left the concept theoretical for years.
Ernő Rubik, the creator of the Rubik's Cube, expressed interest in the development of an FTO.[4] Rubik envisioned a version of the puzzle that incorporated only corners and centers, and a patent was filed on February 9, 1981.[5]
On September 15, 1997, Xie Zongliang (謝宗良) from Taiwan applied for a patent for the FTO.[6] According to a report, approximately 1,000 units were produced by Xie in 2008, and there is some indication that the puzzle may have been constructed as early as a decade before that production run.[7]
On July 9, 2003, David Pitcher filed a patent for an FTO.[8] However, the patent was never formalized due to non-payment of issuance fees, allowing the invention to enter the public domain. Between 2001 and 2003, Pitcher developed a working mechanism for the puzzle and later claimed that his design was the first functional prototype of an FTO. However, Pitcher's prototype did not enter mass production, leaving uncertainty on whether Pitcher or Xie created the first working prototype.[9]
Mechanism
The FTO consists of three distinct piece types, totaling 42 external elements:
Corner pieces: There are 6 corners, each occupying a vertex of the octahedron
Edge pieces: There are 12 edges that are located on the intersections of the turning planes
Triangle pieces: In addition to the corners and edges, there are 24 triangle pieces that fill the remaining gaps
The number of internal components varies depending on the manufacturer.
Number of unique positions
Consider these constraints for calculating the total number of unique positions:[10]
Permutations and orientations:
6 vertices (corners) can be arranged in 6! ways, with 2 orientations each
12 edges can be arranged in 12! ways
Two sets of 12 centers (triangle pieces) can be arranged in (12!)² ways
Restrictions:
Only an even number of vertex pieces can be flipped (division by 2)
Vertex and edge permutations must be even (division by 2)
Centers are grouped in identical triplets (division by 3!⁸)
The puzzle's orientation is fixed by one unique piece, offering 12 possible (division by 12)
Combining these factors, the total number of unique positions is:[11][12]
Records
Although the FTO is not an official World Cube Association event, it has an active speedsolving community, largely due to the resurgence of newer hardware in recent years. As one of the most frequently featured unofficial events at official competitions, there is growing advocacy for the FTO to gain official recognition by the WCA.[13]
