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I have a model (see image) and I am trying to animate a destruction.

But it doesn't seem possible, since XNA is using only bones to animate. So my question is:

Which workflow should I use, to animate 4 independent objects (being one big model), which lie on top of each other?

Regarding this model:

enter image description here

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Why not apply physics to it the moment you need them to go down? – Sidar May 16 '13 at 14:39
For two reasons: I have not added a physics engine to this 3D-Game, since there aren't really good ones out there and secondly, I'd like to solve this in Maya – IMX May 16 '13 at 14:42

Each object should have its own bone. Each bone should be unconnected to the others and able to move freely. This allows you to animate each bone, with position and rotation, while still keeping the model as one. Each bone is really just a matrix to apply to the vertices under it's control. It's simple to imagine applying a translation and rotation to each group of vertices that make up each portion of the complete object above. Allowing them to separate and move independently of each other.

You should use the 3D modeling/animation program you're most familiar with. If your program allows for simulations with physics, you can utilize it to physically simulate the collapse. Alternatively, you can do the animation by hand, using key frames. Animating by hand will be challenging, but should be simple enough with the right approach. I would start by moving the top and having the near bottom one collapse, moving the other parts to follow. But, really, that's an artistic question and there are many different ways to do it.

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It can't be, that every rock of that model has its own bone with its own root. Because then, XNA gives me this error: Node has more than one BoneContent child. Unable to determine which one is the skeleton root. The model has to be one skeleton. – IMX May 16 '13 at 18:07
I didn't say multiple roots. You have one root, and multiple bones. You just move the bones independently of each other. Either making them all children of the root bone. Or making them "unconnected", I'm not sure what that entails with Maya, but you don't want them to utilize their parent rotations and translations, just their own and the root. – Byte56 May 16 '13 at 18:23

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