Today, we are going to address some topology stuff. Particularly about joint like elbow.
Disclamer : This is not a tutorial, neither some good practice. Here is only some research/work I did. There is probably other ways to do, and probably some more efficient way …
I tried many way of doing, in order to have some correct deformed joints, fold in only one way, about 150°, exactly like elbow.
It’s a cylinder, cut in half size, with 2 bones, and basic Weight Paint.
As you can see, result is quit bad:
First step is to activate Volume Preservation on Armature modifier.
Result quality increase a little bit, but is not good enough yet:
Here I changed topology, in order to have a deformation limited to joint area. I added 2 loopcuts.
Now, we have indeed a deformation only on joint area, a small volume loose. But we have some face intersection when angle is too high:
Change topology again
In order to avoid intersection, I changed topology again.
Main disadvantage is that now, joint can only be fold in one side. That is how elbow works ;-)
We have still some intersection issues, but next step will partially fix them:
I then added a SubSurf modifier:
Now intersection are limited :
Adding Shape Keys
In order to decrease intersections, I added a Shape Key, that is activated by a driver based on joint rotation:
This time, no more intersection. But joint is now “webbed”:
In order to avoid that, we can tweak value of driver of Shape Key. I am not going to perform this step right now, but I am going to test another modification.
Without any modification on weight paint, I then moved location of bones (in Edit mode), to be closer to inside face of joint.
Here is result (without ShapeKey of previous step):
Mix this two steps
Based on two previous steps (bones closer to inside, and shapekeys), we now have:
We have again webbed joint (more that previously). Now time to adjust the driver!
Rotation range must be adjusted, or value must be decreased.
Now result is quite correct :
Adding another shapekey
Inside face of joint is now correct, but outside part is so much rounded. Have a look on your elbow :)
I added another ShapeKey, in order to extrude elbow bone. I kept the first one, of course.
Here is final result :
You know all tests I did :) File with all steps can be downloaded here : Joints
As I said in introduction, there are only tests. I never used this on production.
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