View Full Version : morphing character with changing bone lengths

08 August 2005, 08:32 AM
I have just been asked to quote for a 3D 'evolution' animation with a walking character morphing from a chimp to a human !

I know morphing is pretty easy, but does anyone know a good way to animate the bone lengths whilst maintaining a stable rig and not screwing up the model ?

I guess I'm going to have to produce either a stretched-out chimp model or a squashed-up human model, then animate the bone lengths, but it would be good to hear from someone who has done something similar !

I have a choice of either Lightwave, Project Messiah (Animate) or XSI to do this in, so I will be posting this question in all 3 forums.

Thanks in advance

08 August 2005, 09:12 AM
Hi Jason.

Interesting predicament. I played around in Lightwave and got this rig (attached).

I couldn't simply scale the Z of the thigh and calf bones, because that would scale their children. So I made secondary thigh and calf bones that have no children.

Slide the slider to make the leg lengthen and shrink. It scales the dummy legs and moves the acual legs along the Z. One curiosity I found, the scaling and the moving wouldn't match up, so I had to make a second expression for the moving. Weirdness.

Note that the leg and calf bones that do not get scaled have a strength of 0%. The black ones would be the ones deforming the geometry.

This is a simplified version of what you might do. You probably don't want the kneecap effected by all this scaling business, so you might do a thing where non-scaling bones are near the kneecal and ankle area, and only the center 75% of the leg gets lengthened.

Have fun and let us know how it goes!

08 August 2005, 09:22 AM
Ouch, stretching one bone will lead to stretching all its descendents and I do not think your chimp and human are not of proportional size. Therefore if, for instance, your calf bone is parented to the thigh bone (what would be logical) if you stretch the thigh, the calf will grow similarly.

Moreover, establishing such a versatile rig depends (as always I would say) on the way you plan to animate them (IK or FK, motion capture, keyframing...).
I have a couple of very complex ideas to meet this final result but I do not have any LW license set up on my computer ATM to check if they are valid solutions.

I'd follow this thread thoroughly. I am interested in how you managed to meet this result (as long as you did it with LW of course ;) )

EDIT - I started typing my answer a long time ago, went out with my dog and wow.... Carm3D proposed a solution I had in mind.

08 August 2005, 09:48 AM
Here ( is an MPEG-4 video of the rig in action so telamon can see it without his Lightwave handy. :)

08 August 2005, 10:59 AM
seems to be a great start :thumbsup: You'll have to combine this with a very progressive raising of the root bone.

08 August 2005, 03:37 PM
That is what I did. There is no root bone for this rig, however. The null object (box) is the root.

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