View Full Version : Bullet and Fracture

03-25-2013, 11:45 AM
Hi folks

Well, after a good few years off due to career stuff I'm looking at getting into LW again, so downloaded the demo to see what's what.

One of the new features that interested me is the new dynamics stuff, and so I started to play around. I decided a good test would be to simulate a building demolition implosion, and so after reading the 11.5 supplementary and watching a few videos, I got going. After a few false starts, I produced a fractured plane with a couple of smooth shifted legs, and using the null object breaking techniques in the manual and lots of playing with variables, got the first block to demolish (nearly) as envisioned. However, I then cloned my first object and stacked it on top, but that's where it went wrong. Instead of just sitting there until the hit, the "weight" of the second object seems to create an instantaneous collapse of both objects. Any pointers as to where I'm going wrong?

I'll clean up the scene and post it here shortly.

03-25-2013, 12:18 PM
Right, here's a zip file of the scene.

If you run it as is, you can see the demolition runs as expected. However, when the fracture2 object is enabled, (in the Bullet pop-up), you can see both objects shimmy around a little, then start to disintegrate before the null hits. I've been playing with this most of the afternoon, and I'm stumped! :)

03-25-2013, 02:00 PM
I'm at work so I can't load this up, but one thing to look at is the Glue Strength setting. If this value is small, objects will tent to collapse under their own weight quite easily.

The second thing to look at would be the objects' activation setting, but I'm only familiar with objects that are always active or activate after their last keyframe. (If all else fails, add a keyframe to your objects at the frame just prior to the null hitting to prevent any dynamics happening to them prior to that moment.)

03-25-2013, 02:15 PM
Glue strength is at 100%, with a gradient map as per page 77 of the 11.5 addendum. I'll have my dinner then have a go with the keyframe stuff. Thanks.

03-25-2013, 03:24 PM
Use modeler to copy the fractured object above itself so you have the two in the same layer. Then delete your clone.

Works well here. :)

03-25-2013, 05:02 PM
Cheers mate! I did try it by joining the two objects in modeller and that failed, but didn't take the intermediate step of just having them in the same layer. It's all changed so much since V4.0 on my A4000!

With JR's hint about keyframes, and your help I'm back on track. Tomorrow I'll build some better objects and see how big I can get with my 8meg of Ram and i3. I'll post a video showing my progress. :)

03-26-2013, 05:25 PM
Well, that's a day spent learning how twitchy the Bullet editor is. The slightest adjustment of parameters seems to create a vastly, (and unusably), different result. The Bounciness and Damping controls don't seem to work in any logical way, and any other setting than 50% in the Friction values just seems to blow the model up within the span of a frame. Really not as productive as I hoped.

03-26-2013, 05:28 PM
It takes a lot of experimentation, but when it works it works great.

I've also had some luck in using "concave whatchamawhoosits" instead of "mesh" for the collision shape on parts bodies, altering the collision detection distance, making sure nothing was set to 0%, etc.

03-26-2013, 05:49 PM
Oh, I'm not saying you can't get reasonable results, just that fine tuning seems far harder than it should be. ;)