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I try to make a glass rotate till it hits ground then break with rigid body and cell fracture, however I dont know how to make glass remain together and only break till it hits the ground?

Image a glass window rotate falls down then break in pieces.

Thanks in advance!

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1 Answer 1

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That's not hard. You need a Rigid Body Constraint... well, a lot of them.

The Fragmentation

  1. Create the Quick Effects > Cell Fracture. (Requires the enabled Cell Fracture add-on that comes with Blender)

  2. Move the created fracture objects into their own new collection (M)

  3. Make them rigid bodies with the menu entry Object > Rigid Body > Add Active

  4. Make one of the objects the active object by selecting it but keep them all selected

  5. Add the Contraints with Object > Rigid Body > Connect. This can take a second or two! connect contraints

  6. Hide the original model

  7. Select all constraints, and move them to their own collection to keep things organized

  8. Select one constraint to make it the active object and go to the Physics tab to see the settings.

    • right-click the collection > Select Objects to select them all
    • now press & hold Alt and uncheck [_] Disable Collision
    • press & hold Alt and enable [X] Breakable
    • set the Threshold to a low value like 1.000. Confirm it with Alt+Enter so the setting for all selected contraints will be changed.
      contraint settings
  9. Add a plane (the ground) and choose Object > Rigid Body > Add Passive

  10. Run the animation. Happy destruction!

kaboom!

The Rotation During The Fall

There are several ways to add rotation to the falling object.

Method 1: Push it or make it jump off the cliff

You just need a little plane (passive rigid body), place it half under the object that you want to destroy, and let the physics do the work:

cliff jumper

Method 2: Animate the Initial Rotation

The answer to this question seems to be simple. But there are several pitfalls. Let's do it step by step. The result will look like this:

animated rotation

First, place the Empty at the center of mass. You can use the original mesh for this (menu Object > Set Origin > Origin to Center of Mass (Volume). Then use 3D Cursor (Shift+S)

Now parent all fragments to the Empty and you can do a very short animation for the Empty. In the example, it's rotated by 45° within 6 frames. This will give the fragments momentum.

animated empty

To make the fragments follow the rotation you need to check the [X] Animation checkbox. This way it's not controlled by physics but the Empty.

To make this work for all fragments, tick the checkbox for only the first fragment. Keyframe the [X] and [_] at frames 1 and 6. Then select all fragments, make sure the first (keyframed) fragment is the active one (selected last) and link the animation data by menu entry Object > Link/Transfer Data > Link Animation Data (shortcut Ctrl+L).

rigid body animation option

The Cracks! - Yet Another Problem

Once you added the rotation momentum to the rigid bodies you will notice an ugly issue. There are cracks in the object:

cracks!

From the distance, this might be not noticeable but in close-ups it is.

Unchecking the [_] Breakable option in the Physics options of the rigid body constraints or increasing the Threshold value does not help to get rid of this.

For the final animation, I've let fall the original object and swapped its visibility with the hidden rigid body fragments right before it hit the ground.

Just parented the original object to the first fragment and keyframed the visibility for the original mesh and the first fragment. If not done yet, link the animation data of the first fragment to all fragments as described in method 2 above.

(I'm not sure if that is the best approach but it did the trick.)

final animation

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  • $\begingroup$ Thanks for responding! However, how do I make the cell fracture objects rotate as a whole? $\endgroup$ Sep 19, 2021 at 9:48
  • $\begingroup$ Oh, sorry, I've missed that part. It turned out to be an interesting question that was not as easy to answer as it first seemed. I've updated the answer above. $\endgroup$
    – Blunder
    Sep 19, 2021 at 16:03

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