rigging up a expandable accordian style neck

# 1 25-03-2006 , 06:29 AM

Registered User
Join Date: Jun 2005

Location: los angeles

Posts: 1

rigging up a expandable accordian style neck

Can anyone tell me how to set up a neck on character that has to
be expandable like an accordian? Basically what I have is a nurbs neck built like an accordian with a sphere head. I put bones inside the neck and then set up an IK Spline on that. Then I skinned the neck to the skeleton. I selected the cv's on the spline and clustered them and made nurbs circle controls for each of the four clusters and parented those to each cluster. Then I grouped the sphere head to itself and point constrained that to the top joint of the skeleton.

Now it moves side to side or all over when you grab any of the controls BUT how do I get it squash or stretch like an accordian? Someone suggested a set driven key.

I want the head to stay with the neck where they meet but also be able to freely rotate the head and animate it too of course.

It would be like a duck like character let's say, but with a more accordian neck that can expand and contract. Also I would like the base/bottom of the neck to remain stationary and not bend or deform when other parts are bent.

Any ideas??

Here is an idea of what I've done so far. This isn't the real one I'm doing, but I can't share that at this time.

Attached Images

Quote

# 2 10-04-2006 , 07:41 PM

Registered User
Join Date: May 2004

Location: Utah, USA

Posts: 369

I haven't tried this but I think you could make a series of bones that zigzag up the length of the accordian(start from the bottom and build the zigzag skeleton up (Y direction)). Then, try hooking up an IK from the bottom joint to the top joint. If it works, you should be able to grab the IK handle and stretch and bend the skeleton. Now for the hard part; you have to weight the accordian to the zigzag skeleton.

Like I said, I never tried this but it's all I've been able to come up with....

Quote

# 3 15-04-2006 , 10:43 AM

Registered User
Join Date: Mar 2004

Location: Wales, UK

Posts: 6

Hi

Just been reading the Art of Rigging books from CGToolkit. In there the show how to rig a spring using a wire deformer through the centre of the spring. This allows the spring to deform with changing its coil diameter.

You should be able to use the same idea for the accordion and connect a set of staight line joints(through C/line) to the wire deformer. Then set up some utility nodes to calculate total length of joint chain and divide this by number of joints and plug this into the scale of each joint (usually X axis).

Using utility nodes is the best option as an expression has to be evaluated each frame where as utility nodes are a direct connection.

Visit Joe Harkins website for a set of scripts to help set up the above joint chain.

Joe Harkin's web site.