Tuesday, 31 May 2011

Free the Key

Free the Key
In my recent batch from Puzzle Master I received the Free the Key puzzle made by the company themselves and rated as an 8 out of 10 (demanding). It was designed by Oskar van Deventer and has been available in slightly different form factor from a number of other companies. I think the Puzzle Master version is the only one currently on the market today. It is supplied with a solution (although being fairly stupid, I didn't realise this and threw it away with the packaging before I found out!!!)

It is a pretty big puzzle measuring 11cm long with the disk being 4.5 cm diameter and a very decent weight. It feels fantastic in your hands. It consists of a very large key with protrusions of varying height on either side and a brass disk at the hilt of the key. The disk has slots cut in it of varying heights to take the protrusions. Overall this is a good quality puzzle - the finish is not quite as good as the Hanayama puzzles (there are some casting marks on the key and the brass disk would be nicer with a glossy finish). I think this is pretty good value for money - you get a decent bang for your buck.

The aim is to separate the 2 pieces and then put them back together. No problem I thought, how difficult can this be? They rate this as level 8 out of 10 (demanding) and I think it is probably a 7, as everyone solves it in a fairly reasonable time. However, it is not as straight-forward as it looks; it is not just a case of progressing forwards and rotating the disk one way or the other. There are plenty of dead ends requiring back-tracking, rotating to a different section of the disk and then trying again. The first time I did it, it took me about 10 minutes to take it apart and (shame on me!) about 20 minutes to get back to the beginning.

Free the Key open
There is no way you can work out in advance what to do, it is like wandering through a maze - you have to just wander and see where you end up. If you are mathematically inclined then it has been modelled in Mathematica and a paper written on it (you can find it here).

I have taken this one to work and left it out for all and sundry to pick up and play with. It is so big and shiny that no-one can resist picking it up. Only one person has given up on it (they didn't try for long) and everyone solves it eventually. I love watching people do this - the shock on their faces when they suddenly realise that they have to back-track is just great to see! I first solved this about a month ago and have done it many many times since then. I still cannot remember a solution, I need to solve it fresh every time. This makes for a great puzzle as repeatability is always a bonus with puzzles. I have tried doing it against a clock and even blind! I can do this one now in about 25 seconds and do not need to look at it at all. I do the whole thing by feel alone and it still gives me a buzz each time.

It has met with absolutely universal approval and I can really recommend it to you as a coffee table piece. Even though it doesn't have the finish of the Hanayama puzzles, it is still attractive and has been a big hit with my friends and colleagues. Buy it!!!


  1. What happens when you take the ring off if you flip it around and try to put it back on? Can you still get back to the start? I would imagine it is possible, because the key is symmetric.

    That is quite an impressive analysis using Mathematica! I do not have this puzzle but your review makes me want to go get one!

  2. George, I have tried flipping the disk over and it makes little difference apart from you have to rotate in the opposite direction. This has given me an idea for my own harder version with a triangular profile - it would have a central circular shank and the pegs would come off at 120degree intervals. Not sure how to start yet!

    It's pretty cheap to buy and considering it is not difficult to do, it is curiously satisfying! You won't regret buying one.

    I don't have Mathematica so couldn't use the workbooks myself but it was quite an analysis!

  3. I would imagine you can get to the map without using Mathematica. The hard part is going between a physical design and the map.

    I have analyzed the Cast Disk, and when you flip the disk around and reattach you get a similar, but subtley changed map. I can send you the write-up on this if you like.

  4. I have to say that the mathematica produced maps are quite difficult to translate into actual disk movements! The flat maze produced is quite hard to visualise and when it is wrapped around the shaft you really need the ability to manipulate it in 3d to see it properly. I can't do that in my browser (does it happen in others or do you need the program for that?)

    I look forward to seeing your analysis - you are much more of a mathematician than me. I only did 5 years with the Open university in maths! A very very long time ago!!!

  5. After looking at the Mathematica map, I noticed that the path of the first half of the key and second half solution are identical. some pegs just go through to tall holes

    1. This may be true but the disk is not oriented the same way when it arrives at the second half - this means it is not an identical set of moves for that section of the puzzle.



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