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I have been trying for way too long now to have a shape composed of a bunch of cubes struck by another larger rectangle type object. After surveying a ton of tutorials and the entirety of the literature on stack exchange regarding this problem, I am still stuck. Here is the issue.

The ensemble of cubes is free floating (not dynamic) and needs to maintain that property until struck. No matter my settings for the animated and dynamic key frames, I either end up with:

  • Cubes falling before struck
  • No collision occurring (they simply overlap, as if they aren't rigid bodies)
  • A dramatic though entertaining explosion of the cubes

Here are all of the different things I've tried (with no success):

  • Manipulating the Enable Deactivation and Start Deactivated options (for all possible combinations of the colliding and collided with objects)
  • Changing from convex hull to mesh
  • Animating the animated and dynamic key frames (for both and neither) and simply testing them when on and off
  • Fiddling with the collision margin and margin

I cannot seem to get this to work. I don't know what pictures to post because I've tried so many different solutions (and I don't know which wrong solution will give the most insight to the community). I will use Blend-Exchange to upload the file. Please help it would be much appreciated! This is my first ever created blend file and I want it to work!!

EDIT: Unfortunately, Blend-Exchange is having an issue uploading my blend file ("error uploading") so I am unsure what to do now

EDIT: Perhaps this will work (using PasteAll): http://pasteall.org/blend/index.php?id=51817

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  • $\begingroup$ Thanks for the help Edgel3D, however, I still have a little bit of an issue. Using an invisible plane seems to be a good idea, but the issue concerns my stacked blocks. ![enter image description here](i.stack.imgur.com/aoIDp.png) As you can see from the image, my 'b' is composed of blocks that would not maintain their form when placed simply on an invisible passive plane. Note that the 'i' will swing into the 'b', and shatter it into its cubes. Furthermore, given that solution, would I be unable to animate the cubes prior to the collision? Thanks $\endgroup$ – Eric May 29 at 19:21
  • $\begingroup$ I'm off to experiment with this. Watch this space. Would it be more prudent if we shift the comments relating to the answer given, down ino that ? If I come up with a solution, it will be appended to that. $\endgroup$ – Edgel3D May 30 at 4:29
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This approach took a shortcut in that the individual cubes forming the letter 'b' were all joined as one object. The explode modifier was used to break it up. This avoids the physics problem.

The shards that result from the explosion modifier have been rendered invisible in favour of cube shaped particles to maintain the illusion that the cube-stack is what is breaking up.

The explosion modifier and the original 'b' was, at the appropriate frame, switched to a second emitter, (3D &'B' shaped) that emits the same sized and coloured cubes as used to form the letter.

Note - there is an invisible catch plane placed just above the visible ground in order to catch the cubes as they fall.

When particle objects sit on the ground, they do so at their origin points. This would usually be at their center, so they 'sink into the mud'. To keep their feet dry this catch plane is set up with the required physics and a little higher than the visible ground which becomes just a prop.

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After some two days of experimentation and with your apparent leaning to use the original cubes for the break up, I came up with this...

To use the stacked cubes in your uploaded Blend file, the timeline was set to frame 1, then each and every cube had it's physics reset by switching the Rigid body button off then on again. That restored the physics.

As there are some 1040+ cubes only a quarter were actually processed this way.

In order to hold them mid-air, the Animation box is ticked and Dynamic box unticked, and both keyframed, again for each and every cube.

At the impact frame these two tick-boxes have to be keyframed again but in reverse. The cubes then fall to the ground.

(ignore the green bar)

Granted it looks good but of the two methods, the Explode modifier gives far better control over the break-up appearance, directional bias, and general cube behavior. With the letter solid it's also a simple matter to manually animate it's lurch on impact.

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You can skip the reversing tick boxes step, by rendering the cubes dropping from frame 1. Animate a solid duplicate of the letter in a separate video and mix the two in the VSE.

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