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I have a tower of flat boxes, but the simulation is not stable. I have tried with split impulse turned off and on.

I have tried:

  • setting the collision shape to box, convex hull, and mesh
  • increasing the number of steps per second and iterations per step (though this does improve the stability, it still eventually collapses without outside influence)
  • enabling deactivation
  • start deactivated (but as soon as an object touches the tower, it gets very "bouncy")

I have even tried to gradually increase gravity, hoping that the boxes would eventually gently settle all opposing forces (gravity and contact constraints). This blend file shows that gravity is squishing the boxes a bit.

This technique, combined with enabling deactivation seems to work alright, until an object activates the boxes (on contact). Does anyone know of a less hacky way to prevent a tower of boxes from bobbing up and down like this?

Is there a way to make this kind of tower stable without resorting to these kinds of tricks?

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  • $\begingroup$ I cranked Steps per second up to 400 and then it stayed upright even after simulating 10000 frames. $\endgroup$ – gandalf3 Mar 25 '15 at 22:34
  • $\begingroup$ Hm.. I don't see this as being a duplicate since in my question I mention that I've already tried the solutions presented in the answer to the similar question. The start deactivated trick doesn't work because the tower starts bobbing up and down on first contact. Increasing the steps to a huge number may help in rendering, but I'm not sure it will work for a real-time game. $\endgroup$ – snapfractalpop Mar 26 '15 at 2:03
  • $\begingroup$ Oh, is this in the BGE? That's different then.. $\endgroup$ – gandalf3 Mar 26 '15 at 2:08
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Put collision shape to box and increase linear and angular damping up to your needs. Remember higher the damping, higher the viscous effect will be (honey like). I suggest to start with 0.3 for both and then try to tune them up until they are stable.

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You can build quite stable towers of stacked boxes. The tricks:

  1. Convex Hull. This is the best all-round physics shape. It's the most "stable" with the exception of capsule and sphere - which are unsuitable here. Yes, I've found convex hull better than cube type.
  2. Big collision margins. These help bullet to figure out how to respond to intersecting objects. If you separate your physics and graphics mesh you can make these unnoticable.
  3. If you really need to, increase your physics substeps in the world panel.

A very good reference video about bullet is this one by phymec:
https://www.youtube.com/watch?v=BGAwRKPlpCw

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if the boxes are inside of another object in the simulation Ex. inside another cube the boxes will instantly fly away from each other.

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