Physical link between some vertices of a cloth object and a soft body object

Question

I was wondering if there is a way to pin some vertices of a cloth object to a soft body object with a sort of physical link with a fixed-length.

To be more specific, I would like to use a cloth object pinned on the "ground" to hold a flexible pole (soft-body object) in a wind force field. Here is a scene for example :

• The pole is a simple string of vertices with a Skin modifier and Soft-Body physics.
• For the cloth object, there is one vertice pinned on the ground and I used hooks pinned to the vertices of the arc part of the cloth and keyframed "Child of" constraints so hooks can follow the pole dynamics at some point in the scene.

But as you can see, the cloth is not holding the pole since Child of constraints are not really made for this purpose.

Do you have any idea on how I can create those links between the cloth and the pole ?

- EDIT : after some research, it seems that blender is not able to make cross-simulation between physics systems (where the state of each system is dependent of the state of the other ones)

Answer 1

Yes, you can do that:

We'll start by making an empty at the position of the pole that we want the the cloth to be controlled by, then we'll vertex parent that empty to the pole.

Next, we'll create a hook modifier for the cloth object. To be affected by a hook, a vertex needs to be assigned to the hook. The easiest way to make a hook is to select a vertex in edit mode and ctrl-h hook to new object, which creates a new empty and hooks the selected vertices to that empty.

This hook modifier needs to be above/before the cloth physics, and any hooked vertices should be assigned to the cloth pinning group. The cloth pinning group should have a stiffness of 1. The hook modifier should probably be set to no falloff (as shown). When this happens, the hooked vertices will follow the hook, and the cloth physics won't affect those hooked vertices, which will then drag the rest of the mesh with them to preserve the cloth physics.

We now have two empties. The only thing remaining is to join them. I recommend doing that with a "copy location" constraint on the hook empty, targeting the soft body's child empty. Now, when the soft body moves, it will drag its child, which will drag the hook, which will drag the cloth.

Physics works by generating forces according to a base mesh. That means that wherever you place the hook at frame 1 will generate the rest shape for the cloth physics. Because of that, you may wish to set the influence of the copy transforms constraint to 0 at frame 1, to set rest lengths, and only keyframe it up to 1 a few frames into the animation. (That's why I recommend doing this with a copy location constraint.)