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How
to rig the arm.
The
most common and easiest approach is to create three bones, one for the
upper arm, one for the forearm, and one for the hand. This will work fine
in many cases, but if you want your character to look as good as possible
while animating, then you'll want to go with a more complex approach.
The reason that the basic approach doesn't look as good as more complicated
rigs is because when the hand rotates from side to side, the forearm stays
fixed.
Look
at your hand and rotate it from side to side. You'll notice that the wrist
rotate right along with the hand, but as you go down the forearm the rotation
becomes less noticable. And if you look at your elbow while your hand
is rotating, you'll notice that it doesn't twist at all. So basically
we need some way to emulate the lessening of the twist down the arm, and
using one bone for the forearm doesn't do that.
So
here are the different rigging techniques I know of.
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Technique
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Pros
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Cons
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The
basic three bone setup.
*Click
here for step by step instructions.
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Very easy to create. |
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The skinned model doesn't deform well around the joints, especially
the wrist. |
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Create
two extra bones in the forearm to act as the radius and ulna in
a real arm.
*Click
here for step by step instructions.
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The forearm bones behave in a more natural way when the wrist is turned. |
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More complicated setup.
• It's hard to get the skinning to look right in the forearm
and wrist areas. |
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Use
the "wrist twist" method, where the forearm is broken
up into smaller bones so that the forearm twists more naturally.
*Click
here for step by step instructions.
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Easy to skin with this setup.
• Results in a natural looking wrist motion.
• You have the option of using fewer bones to save on memory,
or adding more bones for a more natural look. |
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Takes longer to wire the bones properly.
• Requires some math :). |
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Use
the new Max 5 SplineIK Solver with multiple bones in the
forearm to twist the wrist.
*Click
here for step by step instructions.
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Has all the benefits of the method above, but is quicker to set up
because you only need to use wiring once. |
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Doesn't work on older versions of Max. |
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Add
a biceps bone so that the biceps area of the mesh will bulge and
contract as you animate the character bending its arm.
*Click
here for step by step instructions.
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You can achieve fairly realistic muscle movement without the need
for modifiers or deformers. This is very important when exporting
characters to a game that doesn't support anything other than assigning
vertex weighting to bones, such as Unreal Tournament 2003. |
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Requires a bit of extra set up time.
• Adds a bone (or more) to the overall bone count, which will
increase the memory requirements for the character. |
You
can also take each of these setups one step further and turn them into
a combination IK/FK rig. I'll tackle this at a later date.
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