# How to animate an explosion in a certain direction? Why is my shatter going in the opposite direction?

## Problem

Hi. I animated a ball going through a window. The window shatters in the direction the ball comes from, but I expect it to shatter the direction the ball is going to.

1. In Physics Properties, both objects have rigid body
2. Both have Type: active and Settings: dynamic on.
3. The ball has Settings: animated on.
4. I'm using cell fractures to fracture the glass before the ball hits.
5. Each fractured piece that shatters in the wrong direction has Dynamics -> Deactivation -> Start Deactivated turned on.

I've spent the past day watching YouTube videos, etc, and the only solution I came up with is to flip the window over on the axis 180 degrees. It works, but if I did something more complex, huge problems come up then.

Any ideas?

Thanks!

• I use an invisible passive object such as a vertical plane to 'guide' wayward debris. In this case you could try placing the wall just outside the window so very little can go back out. Sep 6 at 23:35
• can you provide blend file? Sep 7 at 2:18
• No problems - give us a day to put an answer together. Caught up at the Mo. Sep 8 at 4:42

This has been posted in response to @John MC 's request in the comments above. It also addresses the problem outlined in CyberHavenProgramming's question...

It's a simple example of influencing cell fractured segments (and particles too) to travel in a desired direction and velocity. (Blend file is below)

A plane is simply placed vertically, like a wall with 'passive' physics to repel them. For particles it will need collision properties as well or an additional deflector to take care of those.

This deflector had been placed close to and this side of the glass to force enough shard velocity to visually match the ball's. It's 'Margin' has also been wound up to 0.4

With the deflector's "shape property" set to 'Convex Hull' or 'Mesh' in the physics properties, and the 'Collision Margin' set high enough, fragments can be forced away at different velocities.

The deflector's mesh shape can be anything that will shape the way segment's will gather or fly apart the way you want them. Yet others can be added to act as a 'shield' for nearby (non-physic'd) scenery objects.

Shapes such as a half cylinder can act as an overhead hood to prevent debris from flying too high perhaps, or another laid at ground level to reinforce the ground's properties when too many escapees are falling through and where fiddling with ground settings will cause side effects elsewhere.

• Worked perfectly. Thanks! I also added an invisible material on the deflector with blend mode set to alpha blend, and turned the alpha to 0. Sep 9 at 18:55
• Sounds like a good move. I did this in vers 2.77 so things might be a little different in the latter versions. When you experiment with different shaped deflectors you find you have good control over CF's and particles. It's good to hear that things work out. :) Sep 10 at 0:00