Is it possible to have two (or more) Soft body objects collide in Blender?
I have tried enabling self-collision, but distinct objects don't seem to interact with each other at all.
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For each soft body object:
Add Soft Body,
Empirically, it seems that in the Modifier tab, Collision should be below Soft Body.
Adjust the settings to your needs, then from the "Cache" panel of any Soft Body object, "Bake all Dynamics".
In this setup all the objects seem to be both affected and affecting all the others
(however Blender warns the user about a "dependency cycle", as if for some reason this wasn't considered proper behaviour... see also this question)
"Self Collision" is for the same object to collide with itself, not other objects/simulations. Each soft body modifier acts as a separate simulation, they can't interact.
So, select all the softbody objects that will collide, then "Join" them (Ctrl+J) into one object. Now the separate parts within the same object can use "Self Collision".
(Combined objects are not much more difficult to manage, just different. You can still manipulate the separate parts within the same mesh like separate objects, just select a vertex of a part, then "Select Linked All" (Ctrl + L) to select the part for manipulation.
Or you can keep a copy of all the separate objects in a hidden layer that you manipulate, then join them when you're ready to simulate. You may have to combine/finagle the materials some, but that's for another question. )
(Also, depending on what you are trying to accomplish, you may find "Cloth Simulation" to work faster and give better results than Soft Body, especially with self collisions.)
If You just want a jello-like reaction, you can add a soft body and a rigid body to the objects. For this you do not have to combine the objects. I learned this just by testing.
If you want a collision make sure to add a collision modifier as well. And feel free to test different values in the physics tab. If you don't want clipping I would check the box "face" in the soft body edges tab.
Warning: all this does is add the illusion of bouncing. It is actually hitting the rigid body so make sure you have a soft body that can support itself. If you don't the "skin" of the object will melt away while the rigid body stays, it is invisible but still affects the collision. This limits the scope of the method to jello-type objects only. You can sort of lessen this by changing the rigid body shape from default "convex hull" to mesh.
Also you should make the friction (above .5 for best results) of the soft body the same as the rigid body or else they will separate and weird things will happen.
Also select stiff quads or else it will start freaking out. It is sort of humorous to watch though.