Download Cage's chain_maker4b.py. Create a short chain, orientated on the y axis, and examine the resultant cr2. I designed the template cr2 that the chain maker uses, it's so long ago now that I forget the details, but I think it works something like this. The key to the whole thing is the two extra translateY channels in each link. These act much the same way as the normal 'Offset' channels. One translateY moves the effective origin of the link, then a rotate channel rotates the link round the new "origin", then the other translateY puts the origin back where it was to start with. The rotate channel sandwiched between the extra translateY channels changes depending on the orientation of the link. In the first link it's the rotateZ, then in the second link it's rotateX, then in the third link it's back to rotateZ, and so on, alternating for each link. In this system the order of the channels in the channel stack is very important.