Maya for 3D Printing - Rapid Prototyping
In this course we're going to look at something a little different, creating technically accurate 3D printed parts.
# 1 07-01-2013 , 05:06 PM
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Join Date: Oct 2011
Posts: 4

Spline IK - Centipede

I'm working on a weird body-type: a monster that's basically two torsos joined together, with a third pair of arms at the "hip" area where they meet. So sort of a six-armed centipede character with a neck & head at each end. I think I attached a screenshot, if I did that right.

His bound spine is controlled by a separate driver chain, which extends from the bottom neck base to the top neck base. That driver chain has a spline IK, running from the bottom neck base upward.

The spline curve is smooth-bound to three joints: the spine bottom, mid, and top. Those joints are then parented to control curves.

My sticking point is rotating the middle or bottom of the chain. The last point in the chain (the base of the top neck) stays put, because that chest control curve isn't moving, so the last bone stretches while the rest of the chain follows the curve.

My only limitation is that the bound joints all have to be connected, since this rig is for a game. Is there a better setup I should be using for an anatomy like this? Or is there something I can change about the rig to prevent that last bone from stretching when I bend the spline IK?

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# 2 08-01-2013 , 03:39 PM
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Join Date: Oct 2011
Posts: 4
Okay, I think I have this figured out:

My spine was a spline IK whose curve was smooth bound to some floating joints, which I parented to controllers so I could tug on the spine. By itself, the joints can be moved wherever without stretching my bound bones, they just conform to as much of the curve as they can cover.

The reason my topmost joint was stuck in place: the neck has its OWN spline curve with some bound joints. The joint that was anchoring the bottom of my neck spline in place was parented to the chest controller, so it forced my neck bone to go wherever that controller went instead of obeying the curve.

I fixed it by parenting the neck spline's anchor joint to my spine driver chain's topmost joint. Now it follows the spine curve without stretching.

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