View Full Version : Rigging an accordion bellows?

08-22-2010, 08:51 PM
I play accordion, and I was contemplating what it would take to rig a virtual accordion bellows in Lightwave. (There will be a bit of 'thinking out loud' in this post.)

I don't see any way around using a fair amount of expressions. One thing to remember is bellows don't just go in and out, they also bend/tilt/shear.

The one idea I came up with would be to have morph maps for the top and bottom of the bellows, closed and expanded. The morphing would be driven by expressions that measured the distance between twin sets of nulls at the tops and bottoms of the two rigid pieces of the accordion (the [treble/keyboard] and sides). So, if you pull the chord side straight out, both morphs are driven equally, but if you tilt it, they are driven unequally.

This would work, but only on a straight line. It would be far [B]better if the points of the bellows were reacting in some kind of stretchy, IK-ish way. Maybe the new-ish stretchy bones would work, although the weird, jointed behavior of a bellows is not really a straight stretch.

Now I recall that, somewhere, Proton did a video tutorial on accordion style closet doors. That may have involved some cheating though...

In the optimum rig, the points of the accordion corners would accurately remain square, while pointing at the other side of the bellows.

Ryan Roye
08-23-2010, 04:33 PM
try out this video, you may be able to fix something up with something similar to this:


Otherwise, I'm not certain.