Storm - Specific Soft Body Collision Anomaly Fix
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What Is the Issue?
In Storm soft-body collisions (and likely other simulation elements like Cloth and SPH Liquids) can result in wildly exaggerated reactions to movements or rotations of the collision object. What is causing this?
This problem only happens with Storm simulations set up in nodes. It is not an issue when using the Classic Interface. I typically create an alembic (*.abc file) for my collision object animated in Lightwave. I load the alembic into Storm via the Read node. Because of the differences in scale between Lightwave and Storm, I change the Read node's Scale setting from it's default value of 1 to 0.01. This will bring the alembic down to the same scale as an *.obj exported from Lightwave into Storm. This is where things get strange:
When a simulated element is contacting the animated collision object, any motion or rotation of the collision object will cause the simulated object to over-react to the change in the collision model to an exponentially exaggerated degree. The problem is a quirk with Storm. The collision object was indeed shrunk down to the proper scale, but the simulated element is reacting to the collision object as if it were still it's original scale. This is why it's reactions are so exaggerated; but only when the collision model is moving or rotating. While the collision model is static, everything appears normal.
To fix the problem you can do one of two options.
- Set the Scale value inside the Read node back to it's default value of 1. Add a Translate node after the Read node. Set the Scale X, Scale Y and Scale Z values to 0.01.
- Keep the 0.01 Scale value in the Read node, but add a Calc-Velocity node after the Read node.
Do either of these options and this very specific but terribly unhelpful collision behavior will be fixed. Enjoy your Storming!
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