# How to apply a soft body simulator on a certain part of an object?

I am currently trying to make a jellyfish animation and I want to make it so that the 4 big tentacles slowly flop around, as if they're in water. In order to accomplish this, I'm attempting to create a vertex group for the tentacles and apply a soft body simulator to it. The goal is to make it so that the tentacles flop around like the moon jellys in this video , while, at the same time, the main body keeps its consistency. Unfortunately, I'm having problems with the soft body simulator. Whenever I apply it, the whole thing distorts like this:

I've spent the whole day trying to figure this out, and haven't had any luck whatsoever. I read another forum somewhere that said to apply a rigid body with the soft body, but I haven't had any luck with that either.

Does anyone know how to apply the soft body simulator on a certain part of your mesh???

Here's a copy of my project.

• The Laplacian modifier would do this. Don't let anyone tell you it's no good when the model itself is also animated. (Blend file available if needed) Note, the tentacle flowing movements would need to be animated. A lattice modifier might also do the job. Apr 8 '20 at 2:24
• Did you try to assign the vertices of the non moving part to a Pin Group? Apr 8 '20 at 9:54
• I have a few actually. I've also been toying with your particular question and (sort of) done that in a hurry yesterday. The demo gif's are too large, so I'll place those and some others with it into an mp4 video and put them up on Dropbox. You can view/download that first, see if anything interests you. Remember though, these are all animated tentacles/tubes. None are automatic like @Bruno 's Stay tuned... Apr 9 '20 at 3:30
• @SMH , The 'collection' video, any of which might do your job is up on Dropbox. The link - dropbox.com/s/30aqyg94rm9xttr/ALL_Tentacles.mp4?dl=0 . Apr 9 '20 at 11:40
• No problems mate! Glad you got there. Apr 23 '20 at 13:56

If you want certain vertices of your mesh (here: all vertices except the ones of the tentacles) to completely "ignore" the softbody-sim and animate like they originally did, three things are required:

1. The vertices you don't want to move need to be assigned with a value of 1 to your goal vertex group
2. The "Default" value in the strength settings of the goal property needs to be one as well
3. The max Strength value needs to also be 1

This basically tells the softbody-sim that those vertices want to be completely animated with their goal, which actually is just their default animation.

Keep in mind however that even though those value-1-vertices will not be affected by the softbody-sim, they still will be taken into account while baking and thus slow down that bake. Don't ask me why.

• thanks your input! I will probably be doing a project similar to this one and I may try you method. Thanks!
– SMH
Apr 23 '20 at 0:20
• No problem my man Apr 23 '20 at 11:59

Cloth simulation Pin Group should do the trick. Just assign the non moving vertices to a specific group and use it in the Shape/Pin Group field of the cloth simulation settings panel.

• How do you make it so that it's not as wrinkly and flaccid? When I used the cloth simulation, it acted too much like cloth. Do you know if there's a way to make it drift like something fleshy or jelly in s current?
– SMH
Apr 8 '20 at 10:37
• just reduced the tension, compression etc... as you can see in the GIF screenshot. With default values, it is too stiff indeed Apr 8 '20 at 11:22

Sorry I forgot to actually post my answer. So what worked for me were these settings with the soft body simulator.

For the control point and the vertex group under goal, I used the "mb2" vertex group.

And for the springs under the edges section, I used the "big tentical" vertex group.

That seemed to do the trick.