Such a fun solution to a weird old comicbook design concept.
I think you're overthinking the mechanism, What you want to achieve sounds a lot like the joint in the old "Magic Snake" toys
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Each joint could rotate like you suggested
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I'd make it like this.
1. Blank off each end of the pipe.
2. Drill center hole
3 Thread through this bolt with the washers held in place with thick springs.
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I think I have that right. The springs hold the washers tight against the blanking space, but give you enough movement to rotate.
Alternatively, buy a Magic Snake and gut it!!
Center the hole in the 'cut' plane so when rotated, the ends line up properly. You could also use a pin & curved slot to limit the rotation to the correct angle.
R/ Robert
Too bad you can't make it from solid billet so it has some real strength. Also, one other possibility is to use a sprung, pass-through steel cable instead of pivot bolts. You'd still want a 'locking' mechanism of some kind to keep it 'clicked' in place, but with the pins & grooves, you could limit the amount (and direction) of the 'twist stress' imparted to the cable.
R/ Robert