Digital humans the art of the digital double
Ever wanted to know how digital doubles are created in the movie industry? This course will give you an insight into how it's done.
# 1 28-03-2009 , 12:03 PM
paldav's Avatar
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dear god help me !!

i want to animate a leg, where the thigh bone changes length, ie hydraulics..

parenting the geometry to a skeleton obviously prohibits this because the bones dont change length, but i like bones because ik is so handyuser added image


free memory low..exception thrown
# 2 28-03-2009 , 06:39 PM
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actually, it is possible to change the length of a bone set in an ik joint structure. What you don't want to do, though, is move it with the translate (move) tool - it won't be as controlled, and you risk seperating pieces.
Instead, I reccommend the following:
create your leg geometry, as well as your ik joint setup. You'll also need one straight nurbs curve for every expanding 'bone'. These curves should be at or just under the length you want your leg to expand, and be included in the joint heirarchy (example - if you want the bone between the elbow and the wrist to lengthen, the curve should be a child of the elbow, and follow its' orientation).
Create a locator, and attach it as part of a motion path to the nurbs curve. Break the connections for the path's uValue (so it's no longer automatically controlled over time), and make sure that the locator is nearest to the non-expanding joint.
Now, parent the expanding joint (in the example, the wrist) to the locator, making sure to check 'maintain offset'. This will mean that when the locator travels along its path, the wrist joint will also 'expand'.
Go ahead and create your ik handles, and set your geometry into the joint heirarchy (or however you normally do this - this type of rig would also allow for expanding joints in organic animation - I think the squirrel in Ice Age has a similar rig). Your expanding geometry piece, however, needs to be set to the location of the expanding joint, and told to be aimed at the base joint (in our example, you'd need to put the piece at the wrist, and aiming at the elbow).
Example attached.
There are many things that can be done to clean this up, of course, for things like additions of animation handles, etc. However, this should give you a basic idea of what to try.

Attached Files
File Type: mb example.mb (97.8 KB, 101 views)

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