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I'm using Blender 2.79 and trying to apply Soft Body physics to a mesh, in this case the Monkey mesh.

I have enabled "Soft Body Edges" and set Edge as a Collision options. I also want to enable Soft Body Self Collision, but when I do and simulate the physics the mesh completely disappears.

enter image description here

Is there a setting that I'm missing?

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  • $\begingroup$ Look at the object's location in the Transform panel; when this happens to me it's light years away or large. Show us your Soft Body Edges panel settings; when this happens to me it's usually because the Pull and Push are set too high. Keep experimenting. $\endgroup$ – lumpynose Dec 5 '17 at 18:11
  • $\begingroup$ @lumpynose this is without changing any of the Soft Body settings, just enabling Edges and Self Collision. $\endgroup$ – hellocatfood Dec 8 '17 at 0:27
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This is easy to replicate by simple adding Suzanne to the scene, enabling Soft Body and enabling Self Collision - and the issue seems to be specific to Suzanne (the other primitives don't exhibit the problem). You can tell something is very wrong by checking the Dimension of the mesh (in the Properties panel (N)) on the second frame - it jumps immediately to some very high values :

dimension

The problem appears to be due to the geometry of the mesh - specifically Suzanne's eyes. The eyes are not connected to the rest of the mesh and actually overlap. This is resulting in particularly odd results with the self-collision - presumably as the overlapping vertices repel each other with almost infinite force.

suzanne eyes

To avoid the problem, in Edit mode (Tab) click a vertex on one of the eyes, hold Control and press Numpad + a few times until the whole eye is selected. Move the eye away from the head. Repeat for the other eye - so that both eyes are no longer overlapping the head.

Now run the simulation and it should behave normally.

I got some interesting results by just moving the eyes a little way away from their original locations. This, presumably reduced the repulsion forces to much smaller values, while still being too close for a stable simulation, resulting in Suzanne being pulled apart rather than being completely obliterated (I think the eyes are being repelled backwards at high speed through her head while the head is being launched forwards) :

rip suzanne

So, in summary, the problem is due to overlapping geometry/vertices. Fix the geometry to avoid such problems.

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    $\begingroup$ Thanks, this completely solves the problem. It's strange that a default mesh would cause such problems but I have no hope of them modifying Suzanne to fix this $\endgroup$ – hellocatfood Dec 8 '17 at 0:31
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Thank you all for this solution! I had the same problem in blender 2.79b - spoiler alert: in 2.80 beta [2019 March 05] this Suzanne's geometry glitch still exists!

These were the steps I took to solve that "rogue vertices" problem, inspired by your answers, especially by Rich Sedman's "look at the dimensions" hint:

  1. Delete one half of Suzanne's face.
  2. Delete all the vertices of the eye that extend beneath the face,
  3. Reconnect the eyes to the rest of the face's geometry by selecting three or four vertices at a time and hitting F for Fill. (I had to use quad and triangle polys, but didn't care that much).
  4. Apply a mirror modifier to make the face whole again.
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