Need help with rigging stretchable tentacle (IK)

I need to rig a creature with tentacles for a game engine. The game engine doesn’t have stretchy bones support (only location/rotation). So I am thinking of the following setup:


A spline going through each tentacle, bones are parented into hierarchy, but not connected. This way they can slide on the spline, stretching the mesh.

I would need to be able to control length of the tentacle by dragging some control bone at the tip (which will also serve as a “foot”) and I would need to be able to “bend” the tentacle in several places to give it desired curvature.

It also need to be switchable IK/FK setup, and it should work when rotated at any degree (imagine octopus would be swimming with 6 degrees of freedom, so tentacles should behave properly no matter what pose octopus is in).

Most likely there should be pole targets, because game engine has IK system, and it requires having pole targets.

I’ve only done a few bipedal rigs, so I have no clue how to rig this one and if it’s even possible to get working.

Can someone help me, please ? Thanks beforehand.

EDIT: Since it’s been over 100 views and no replies, I would consider financial incentive for qualified help.

I am guessing it’s not a trivial task, since no one replied yet :confused:

Yes 100 odd views and no replies, does not beat my record yet, but maybe we are still thinking about it. As you say it is not a trivial task, getting bones to follow a spline that you can also manipulate is no simple task to do successfully. If I was not constrained by the need to have an IK/FK switch and was not further constrained to have non-stretchy bones, I could have posted a rig straight away, but I am still thinking about it…:confused:

Cheers, Clock.

I think there is no need for Fk/IK switch. There is no way I would pose each bone in the tentacle manually :slight_smile: (although I’d need to be able to move whole tentacle at the base). So it would be spline IK rig.

I am not sure if pole targets can exist with spline IK rigs.

Have you checked spline IK works in game as I couldn’t get it working properly when exporting to unity. Doesn’t answer the question sorry but could be another obstacle in your way.

I don’t believe any engine, except maybe UE4, supports spline IK.

I need it to animate the character in most comfortable way possible. The engine supports standard IK (so that when character is on a slope or walking over some obstacles), the legs naturally conform to the slope. That’s why I need pole target. The tentacle bone chain will act like auto-IK bone chain in Blender.

I think I figured this out :slight_smile: There is still some room for improvements (and I haven’t exported it into the game engine yet).

Pre-splike IK setup: http://www.pasteall.org/blend/37477

With spline IK constraint added: http://www.pasteall.org/blend/37478

@motorsep you move the curve handles directly how you wanna animate this setup? you need bones as hooks for your curve handles and a second amature to avoid dependency cycles.
Also you said something about no strecht bone are allowed but your spline ik setup use y stretch.

I wasn’t finished with the complete solution :wink: I only showed that I resolved first part of the problem, namely having stretching tentacle without stretchy bones (although I haven’t exported into game engine yet, so it’s not a fact I solved it :slight_smile: )

I could probably have control bones in the same armature. Even if I have it in another armature, or just have empties as controls, I’d only export deforming armature anyway.

ah ok you wasnt explicit on your first post because i thought no stretch bones are allowed but you mean no strecht for deformation bones, in this case it is much more simpler.

  1. use an ik
  2. copy the bones of the ik for the fk and make child constraints or copy transform.
  3. put a curve inside of the bones and parent with a child constraint the hooks to the fk bones.
  4. put your deformation bones on the curve and make follow path constrainst with different offset to get the same position like your curve handles. Change the influence of the follow path (if you have 4 deformation bones and your curve have 4 handles offset and influence is following… first bone offset 0,3333 influence 0,3333 second bone 0,666 third bone 0,99 (zero bone is zero)).
  5. controll all offsets with a driver.

With this setup you get a ik/fk , individual curve control and lenght control.