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I have a coconut mesh with two sides as if it was cut in half. I can't for the life of me find anywhere online how to get them to fall together, without blender blasting them off into infinity at frame one just because they are touching eachother, and instead fall together as if one then break in half with the two pieces when it hits the ground.

I've tried so many settings with rigid body and collisions with weight, stickiness (which sometimes works, and then will stop working and start bumping them apart again and can't figure out how to get it to not bump apart like it sometimes does "correctly")

I had at one time, got them to fall together without bumping apart, but they split just before hitting the ground plane. Then when trying to fiddle with other settings trying to get it to go all the way to the ground, it now no longer sticks together on the way down and bumps apart at frame one, even though I went back to the exact settings as before....ugh.

I just need these to fall together without bumping each other away as if they are still a whole piece. Then they can bounce/bump apart after hitting the ground.

Oh, if I activate the collision on both sides, one of them gets shoved into the ground plane, which of course can't be used. So at the moment all I can do is use collision on one side, but stuck at that point.

friction doesn't seem to be doing anything at all. Wt doesn't do anything at all either. Unless I change to minimum then it messes up.

Edit: I increased the friction on the one with collision active and it got me back to the point where they both fall...almost to the ground together, but break apart before actually hitting the ground so doesn't make sense, and now one side floats in the air above the ground.....literally no settings have changed from earlier

It appears that one side is hitting an invisible barrier that doesn't exist, which is why it is breaking early and floating. I have deleted the ground plane and started over and it is still doing it, all the settings are exactly the same on each of the mesh's. Can't figure out what it is hitting.

Decided to cut the frames short and render it and even though the simulation shows them sticking together before breaking apart...just above the ground, the render, renders them breaking apart at frame one.... This entire thing is so confusing.

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2 Answers 2

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You could use a technique often applied in game engines: separate the graphics mesh from the physics mesh (in games, you need real time performance, so the physic meshes used for collisions are much simpler than the actual graphics). So to avoid these unwanted mid-air collisions, duplicate the object for use as physics mesh only, make it a little smaller, add a rigid body, disable it for rendering and parent the original object (used as graphics mesh only) to it so they still behave like one entity. This setup:

enter image description here

gives this result:

enter image description here

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  • $\begingroup$ Ohhhh, ok this would probably be what I need to do. I'll tinker around with it. I had gotten it to work the old fashion way and just manually keyframed them for now, but this is something I'll want to look into. Just not sure I understand yet how to make the rigid body smaller than the actual Mesh yet, but can search it. Thank you! $\endgroup$
    – Thai
    Aug 16, 2023 at 9:05
  • $\begingroup$ @Thai i just duplicated the mesh and scaled it a bit down, then added a rigid body. The original sized mesh (with the material) has no rigid body. $\endgroup$
    – taiyo
    Aug 16, 2023 at 9:10
  • $\begingroup$ Ohh ok, that is more simple than it seemed. These have to be grouped/parented or something to stay together? $\endgroup$
    – Thai
    Aug 16, 2023 at 9:14
  • $\begingroup$ Yes, see the outliner setup in the screenshot. You can parent with drag&drop and holding Shift for example. $\endgroup$
    – taiyo
    Aug 16, 2023 at 9:15
  • $\begingroup$ I like this one, it could be more flexible than the constraint method. $\endgroup$
    – Robin Betts
    Aug 16, 2023 at 11:21
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Blender provides a tool for this: Rigid Body Constraint > Connect .

The essential points seem to be:

  • Set on one of the halves, pairing the two
  • Disable collisions, in the constraint
  • Set 'Breakable', and the Impulse Threshold low enough to be sensitive to the collision with the surface

You could also,if needed, transfer normals to the two halves from an intact copy, to hide a seam, using an applied Data Transfer modifier.

This is a minimal example:

enter image description here

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  • $\begingroup$ I like this one, seems to be the more blenderish way of setting up physics scenarios. $\endgroup$
    – taiyo
    Aug 16, 2023 at 14:46
  • $\begingroup$ Ok Awesome, thanks so much for this! $\endgroup$
    – Thai
    Aug 16, 2023 at 23:53

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