Stretchy Ribbon Spine

I've been experimenting with different ways to deform and animate my "Secret Life of Objects" characters.

They all twist, stretch and squash....

Previously I used a stretchy spline Ik. This is a really simple technique which involves joints being spread evenly along, and constrained to, a curve. The curves length, (when it’s stretched) is divided by its initial length and the result is input into the joints scale so that the length of the joint chain matches that of the curve. Unfortunately joints are straight and the curve is… well… curved so the last joint on the chain sometimes overshoots the curve length. Rotate values are passed evenly between the top and bottom controls with an up vector object.

A slightly old but great set of tuts by Aaron Holly uses a “ribbon spine” instead.

Instead of a curve Aaron uses a nurbs surface and parents the bind Joints under follicles created on that surface. The surface is then bound just like the stretchy spline with joints for animation and aim vectors are used to constrain the direction the joints point. Rotational values are output from top and bottom controllers as a percentage relative to the joints position which is then averaged and fed into the joints to evenly distribute them. The center joint, for example, receives 50/50 from top/bottom. 

The benefit is that you can turn/rotate your character as many times as you want and the scale of the joints won’t overshoot – nice. Here is a little test I did with ten joints and three mid-section controllers. They don’t quite rotate the way I want but it will eventually... I also want to create a script for my S.L.O.O rig once I figure out how to get the animation features I want/need - a good excuse to learn mel.