View Full Version : Dynamics Confusion

04-25-2013, 04:11 PM
Hi LW peeps

First off, I'm a bit of a LW noob. I'm messing around with Bullet and for some reason I'm really struggling to get anything going with it.

I'm trying to get a bunch of balls to fall into a large bowl and keep falling in to it. Sounds simple enough, but I can't seem to get this working. I first tried emitters, cause that sounded like the obvious thing. But firstly, I can't get LW to emit balls... Then I tried instances, but here the instances keep interacting with main ball, and they have no dynamics, although the main ball has.

Then I tried to clone the ball in Modeler and then send to Layout. I tag the layer as a parts body and the bowl as a static body and enable dynamics. The stack of balls is above the bowl and should just drop into it. Bullet does its thinking and then...nothing. When I enable the "show instances/something" in the world coordinates tab, and I scroll through the timeline, I see instances of the balls interacting exactly the way they should, but when I F9, none of them render, just the array still hanging in the air... Its frustrating...

Then maybe, just as a starting point, how was this scene set up? (3:41 in the video http://www.youtube.com/watch?v=lcKCe0_-9oM )How did they keep dropping those stacks? What did they do, that I'm not doing?

04-25-2013, 04:33 PM

Just so you know I'm pretty sure you can't use instances with bullet dynamics it has to be built geometry not an instance of it. That's why the main ball is interacting but the instances are not.

I created a few quick scenes for you let me know if this is what you are looking for.




04-26-2013, 06:02 AM
Hey Jason, thanks so much.

Okay, so no instances then. And emitted particles?

I loaded up your scenes and they are doing what they're supposed to. And they render. What I don't get is that I set everything up like you. Also made the layer with the balls a parts layer. The only thing it seems I didn't do was the initial "push" for the balls. I see you animated an initial movement for both scenes. Do you have to do that? Even when there is gravity present? I mean, when you do a simple setup with something hovering in the air, and in the 11/11.5 tutorial examples, and you add dynamics to it and simulate, it falls to the ground, without that initial "push".

Also, in the second scene, you set the ball shapes to Convex pieces. Any specific reason for that? The simulation still seemed to work fine.

Apologies if I sound pedantic. I'd just like to learn by understanding and not just parrot copying. Thanks for the patience and help Jason! :)