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I am making a Rube Goldberg machine in blender and am using rigid body physics for it. My issue is after my ball (an active rigid body object) bumps into dominos which fall down (active rigid body) it pushes a lever on a hinge (with the hinge constraint) which is supposed to release another ball however this ball is floating on the surface which is a passive rigid body object but it should be on the it.

The first image shows how the ball which should be released is just floating. I have tried moving it but it just goes back to this position and I have tried applying all transformations but then it just does something really weird; it just breaks down.

hello

The second image shows how the dominos are also floating but they do fall normally however I have tried moving and applying all transformations as well. The base which all the objects are on is a plane which I changed to shape and is a passive rigid body object set to mesh.

enter image description here

One last thing; I can't get the hinge thing to only move once the domino hits it, I have set the origin of the lever part to 'centre of mass' and this sort of helped but it still moves before the final domino hits it. And lastly, for some reason the dominos jiggle at the start of the simulation. If you have any ideas please let me know.

Here is the blend file:

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  • $\begingroup$ pls provide blend file so we can check it out, thx $\endgroup$
    – Chris
    Mar 30, 2023 at 10:39
  • $\begingroup$ sorry I am slightly new to this how do I add the blend file? $\endgroup$
    – Xander
    Mar 30, 2023 at 10:40
  • $\begingroup$ looks like you found out 👍🏾 $\endgroup$
    – Chris
    Mar 30, 2023 at 11:24
  • $\begingroup$ Your object Layer 2 should be set to Collisions > Shape > Mesh, but the dominos won't push enough to free the ball $\endgroup$
    – moonboots
    Mar 30, 2023 at 12:30

1 Answer 1

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  1. for nearly all simulation (cloth, rigid body, softboy...) you should apply scale + rotation for all involved objects
  2. the collision shape is important:
  • convex hull means: just use an easy "wrap" of the object as collision object (so basically as if you would wrap the object with plastic). So if you look at your "layer2":

enter image description here

This is how Blender "sees" the object for collision:

enter image description here

enter image description here

and then your "dominoes" would stick in that object, so change the shape type to "mesh". This needs longer, but by this Blender takes the mesh as collision object.

  1. often constraints just work with one axis, so the hinge object just works on z-axis:

enter image description here

so you have to rotate the empty as shown in the image.

After doing that, you should see something like this:

enter image description here

here is the repaired file:

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  • $\begingroup$ Hey thanks so much, I was actually tinkering with it and also got it to work by changing the mesh type for the base but I really appreciate this answer as I can actually understand everything, especially with the convex hull thanks for putting the image of 'what blender sees' as I completely didn't understand. $\endgroup$
    – Xander
    Mar 30, 2023 at 13:31
  • $\begingroup$ pls click on the checkmark left of my answer, if it helped you. thx $\endgroup$
    – Chris
    Mar 30, 2023 at 13:42

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