I'm trying to create an octopus tentacle, but am running into
roadblocks and would love suggestions.

I'm thinking about it like creating a chain of "capsules" (cylinders
with hemisphere ends) - I can create a single link of the chain, and I
can call that function in a loop, and I can even scale the chain links
through the loop, but that system doesn't work when I try to curve the
chain.

I'm wondering if a recursive function would help?  Something like
"draw link from origin, move to other side of the link, scale down
slightly, rotate slightly (this is the part that gets me), recurse"

See image for what I mean.

When I rotate slightly, that means the next link's "other end" isn't a
simple offset, but involves math of the current rotation.  Is there a
way to do it internally to the recursion so I don't have to calculate
it myself?  This would also enable all sorts of neat fractal things.

That was excellent advice, thank you!
$fn=50;BASE_HEIGHT = 1;// Angle (curl), Radius (thickness), Height
(length)chain_dna = [    [ 15, .9, 1 ], [ 15, .8, 1 ], [ 15, .7, 1 ],  [
-15, .6, 1 ],    [ -15, .5, 1 ], [-15, .4, .8], [-15, .38, .6 ], [-30, .35,
.4],    [-30, .33, .4], [-30, .3, .4], [-30, .28, .4], [-30, .26,
.4]];module chainlink(dna, idx = 0) {    if (idx +1 < len(dna)) {
angle = dna[idx][0];        radius = dna[idx][1];        height =
dna[idx][2];        difference() {            union() {
sphere(r = radius);                                next_radius = idx+1 <
len(dna) ? dna[idx+1][1] : dna[idx][1];                cylinder(r1 = radius,
r2 = next_radius, h = BASE_HEIGHT * height);
/*                translate([0,0,BASE_HEIGHT * height])
sphere(r = next_radius);                /            }
translate([-radius,radius/2,-radius])            cube([radius2, radius,
height+(2*radius)]);        }                translate([0, 0, BASE_HEIGHT *
height])        rotate([angle,0,0])        chainlink(dna, idx + 1);
}}union() {    // Call the module to create the stacked cylinders.
chainlink(chain_dna);}

--
View this message in context: http://forum.openscad.org/Curved-Chain-tentacle-using-a-series-of-pill-shapes-recursive-function-tp18808p18811.html
Sent from the OpenSCAD mailing list archive at Nabble.com.

A tail/tentacle design (if controlled by parallel cables) needs to be as
untwistable as possible for it to work.

So solutions with ball joints that allow twisting degrees of freedom
will cause your tail/tentacle to become twisted and non-linear to control.
Ideally you're looking for universal style joints between nodes
alternating up with down.
This way the cables remain in the same orientation as they are manipulated.
E.g.
-
http://hackaday.com/2016/10/21/two-stage-tentacle-mechanisms-part-iii-putting-it-all-together/
- https://www.youtube.com/watch?v=8NQH2B-Mnvg
See second video for a commercial toy I can't find in the marketplace.
(Clic something maybe?)
But its a good guide for what to make. Must keep the rigidity up but the
weight down. It gets very heavy very fast as you add nodes.

Please let us know how you get on...