View Full Version : Tentacle-arm/leg Rig (FK and IK)

07 July 2007, 09:51 AM
I am trying to rig a tentacle and i can get the way to mix FK (to pose) and IK
(to pin).

I make a spline IK with a 30 joint, then clusters and then fk joints to control the clusters this way i have smooth deformation and fk controls. But the Ik setup is against me

My tentacles have to work like arms and legs, but with more joints: not hip, knee and ball, i need five joints and the tip of the tentacle (FK) and I need to stick them at objects, floor, etc..

Attached a sketch of the octopus character and a sketch of my fk controls

Thanks again.

octopus sketch (
tentacle controls (

07 July 2007, 11:15 AM
Hi Francis

First of all, nice design you've got there for you character.
Secondly, what app are you using. If you're using maya, maybe you could send me your model and I'd love to try some rigging on the tencacles and then you could reverse-engineer my setup.

It seems to me that you have the fk setup sorted out but that doesn't allow any pinning and you need something to control it in a more IK way. What if you do an ik/fk switch? Then the problem is nailed down to how to make the ik-setup which I got a pretty good idea in my head of how to do it but I think I really need to create the scene to show you how it's done. But then you'll need maya to open it.

07 July 2007, 12:06 PM
Thanks koopatrooper;

I use Maya, and yes, I need IK for pin and something to control ni IK way.
I don't have the model yet but I'm trying making the rig with a simple tentacle polyobject. If you could make a example scene I think I can reverse it and see what happens :)

Thanks at all!

07 July 2007, 05:00 PM
neat concept, i like. :) perhaps instead of working with spline ik, you could consider building your own stretchy bones? attached is an quick example, you can see the big circle that controls the ik movement, and theres an attribute on it to switch to fk. maybe this could be something youd consider.

07 July 2007, 07:09 PM
Amazing, i happen to be working on a snake with the same attributes at this very moment!
lizardj's got the right idea, but one thing i added to mine (cuz snakes don't normally grab things) is a nonlinear sine deformer with a control obj. to animate the sine options.
This gives u a very uniform wavy simulation, but with the ik/fk combo you can get some nice deformation.

snake tut (

07 July 2007, 07:28 PM
Thanks at all! I will test both scenes :D

I attach my scene with the FK works fine (i think) :)

Thanks a lot again

07 July 2007, 05:45 AM
You can get IK and FK to work together if you create 2 duplicate joint chains and feed the rotations of both into an AVERAGE NODE that outputs to your final joint chain. Or, you can have controllers with group nodes above them to "track" the IKchain and double as FK follow-through controllers.I attached a scene.

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07 July 2007, 05:45 AM
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