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Note
The Vellum muscles and tissue system uses a legacy workflow. See the Otis muscles and tissue system for a simplified workflow and recipe examples.
Muscles detach from their bones during their animation ¶
Problem ¶
Your muscles can’t keep up with their high-velocity animated bones.
This may be from the Damping parameter settings on your muscle attachment constraints. For any Vellum constraint, as a point’s position is subjected to various influences (forces, collisions, velocity change), the Vellum solver tries to satisfy all these factors to determine where the point should end up and whether or not the constraint is successful. The damping ratio that is applied to the muscle attachment constraints is designed to reduce the energy or contribution of the constraints during each substep of their muscle simulation. If the damping ratio is set to too high a value, then the contributions of the attachment constraints will be impeded.
Solutions ¶
First, try the following:
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Decrease the Damping value for the Muscle End attach constraint.
For example, if your damping value is 0.01, then try decreasing it to 0.001.
If that does not solve the issue, then also try the following:
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Decrease the Damping value for the Muscle To Bone attachment constraint.
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Increase the number of Vellum Substeps and Vellum Collision Passes on the
Muscle Solver.
Degradation in the crease/fold areas of your tissue simulation ¶
Problem ¶
You are seeing long triangles, tissue surface non-uniform stretching, and tetrahedral tangling in the areas where your tissue creases or folds in on itself like the elbow and knee bend areas of bipeds and quadrupeds.
This is caused by the solver not being able to resolve an extreme tissue constraint vs. collision configuration. For example, when the iteration frequency for the tissue’s constraints and collision passes are set to drastically different values. The visual result of this error is an uneven distribution of energy in the tissue.
Solution ¶
The default Constraint Iterations value is 100
and the Collision Passes value is 10
, which gives you 1
collision pass for every 10
constraint iterations. So with these settings, the constraints will always win over the collision passes as the constraints get to update their points 10 times as often as the collisions.
To generate a much better result in the crease/fold areas of your tissue, try the following:
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Increase the number of Collision Passes. However, collisions are expensive to compute.
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Make sure the ratio between your tissue’s Constraint Iterations and Collision Passes values is much closer to a 1:1.
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Alternatively, you can try increasing the number of Substeps instead of the number of Collision Passes.
Muscle Constraint Properties Vellum troubleshooting ¶
Muscle Ends ¶
To... | Do this |
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Visualize your muscle ends attachments to a bone |
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Fix a muscle end that fails to attach to a bone |
Follow the Visualize your muscle ends attachments to a bone procedure to visualize your muscle end issues. Increase the Distance Threshold parameter in the Muscle Ends tab of |
Fix a muscle end that attaches to a wrong bone |
Follow the Visualize your muscle ends attachments to a bone procedure to visualize your muscle end issues.
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Fix a muscle end that twists unnaturally |
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Fix a muscle end that appears to be poking out of the skin |
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Muscle to muscle ¶
To... | Do this |
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Strengthen constraints that detach easily or fail to stay connected during simulation |
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Loosen constraints that are too rigid and prevent natural movement during simulation |
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Muscle to bone ¶
To... | Do this |
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Fix muscles that are too stiff and lack secondary motion |
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Collisions and velocity blend ¶
To... | Do this |
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Fix muscles that lag behind fast moving bones |
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