A while ago Johan posted some pics on FaceBook of his experiments with variations on a triangular coordinate motion puzzle – he’d come up with a fiendish variant that made similar variants in my collection look rather tame by comparison – and it looked rather stunning, so I gladly signed up for a copy of 4L Co-Mo DD – a rather descriptive name if you can crack the code! [It stands for 4-layer coordinate motion with double difficulty… it’s all clear when you’ve had it explained to you…]
When it’s assembled, it resembles a wheel with an internal ring and an outer rim – closer examination shows that there are four layers to each of those rings, and that they all split apart into three pieces… offset on each layer so that the three pieces form a rudimentary spiral. The basic concept is common to a few coordinate motion assemblies and part of the trick is realising how you need to push or pull the various bits in order to get them to start coming apart…
This little monster has a nasty sting in the tale – it starts out reasonably predictably for these sorts of puzzles, but then as things start coming apart, it goes beyond the point where the first set of interactions hold it neatly in place and it all goes very sloppy … before the second set of interactions begin to bite.
This leaves you with a floppy set of loosely connected - but very much still intertwined - pieces, and a serious challenge to get them all properly aligned and interacting in order to allow the bits to finally come apart – the double difficulty part of the name is well-deserved!
Persevere and you’re rewarded with three separate identical (save for the wood choices!) pieces.
Putting things back together will require a lot of precision and more than a little patience… and a flat surface certainly helps, in my experience – as does a third hand.
It’s a great extension of a reasonably well-known standard, but Johan’s added several lovely twists to make it a serious challenge for even practiced puzzlists… and the stand, that enables it to be displayed semi-open is a master-stroke that makes it display beautifully and invites the challenger.