Exploding only some part of an object in Blender 2.82a (using Explode modifier with Vertex Group?)

Question

I am trying to explode/destroy only some part of an object.
Following Blender 2.82 manual page
https://docs.blender.org/manual/en/2.82/physics/particles/emitter/emission.html
says "You may use vertex groups to confine the emission, that is done in the Vertex Groups panel."
So, it must be possible.

As a test, I created a Blender file, attempting to explode/destroy only the left ear of Suzanne, using Explode modifier. I tried the following:

Added a monkey object ("Suzanne").
Applied "Subdivision Modifier" with "Simple" subdivision algorithm.
Created a vertex group named "VtxGroup_Suzanne__All_vertices_in_left_ear", which contains all vertices in Suzanne's left ear.

enter image description here

Created particle system setting.
Enabled Rotation.
In "Density" field under "Vertex Groups", entered "VtxGroup_Suzanne__All_vertices_in_left_ear".
In "Render As" filed under "Render", chose "Object".
Added "Explode" modifier.
This modifier has "Vertex Group" field, but it seems it does not make any difference in the result (probably because I do not know how to use it properly???)

At this point, when I play the animation, particles erupt out of Suzanne's left ear, breaking down Suzanne little by little. However, the destruction is not limited to the left year. Entire Suzanne starts breaking down.
Some destruction pieces are really big or unnaturally long, such as almost half of Suzanne's face shown in the screenshot.

enter image description here

Is there any way I can limit the destruction only to the left ear (which is vertex group "VtxGroup_Suzanne__All_vertices_in_left_ear". Also, can I adjust the sizes of destruction particles, so that some of them would not be too big, nor too long? I tried setting a whole bunch of settings, but I could not find the solution. Maybe I am attempting this completely wrong? Is there some way to accomplish this in a completely different way? This test file is found here (zipped): Test file for Explode modifier with Vertex Group Thank you in advance for help.

btw if you have any more blender questions there's a Blender stack for that :) — Luciano
– Luciano, Commented Aug 2, 2021 at 14:19

Fishy Apprentice · Accepted Answer · 2020-06-02 13:50:25Z

1

Try splitting the object? If you want to animate the object beforehand, construct the object out of two separate objects grouped, and then ungroup them at or before the keyframe you want them to explode. I hope this helps! :)

answered Jun 2, 2020 at 13:50

Fishy Apprentice

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R0b_stck0vrflw Over a year ago

Thank you for the great suggestion. :-)

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