View Full Version : Collision object "Mode: Stick" with particles

05-09-2008, 10:19 PM
I've got a black background and a black collision object, with an emitter spraying onto it. The particles are meant to hit the collision object and stop, thus painting my object into visibility. Decent idea, no?

Well, the collision object mode called Stick, which presumably is meant to create some sort of sticking action, results in greater than 99 percent of my particles passing clean through my mesh.

Thinking this was merely a matter of upping my Probability beyond 100%, I tried inputting 40 billion percent. LW interpreted this as 1345294336.0 %. Not quite 40 billion, but within an order of magnitude. Result, about 5 percent of particles stick.

Were there another mode called "Pass right through without sticking at all, dammit" or I would try that out, thinking maybe the modes were accidentally mislabeled. Alas...

I could list all the steps I took to make my project fail. It would be like some sort of negative tutorial. You'd all acquire more ignorance in reading it. But I'll spare you that.

Is there any way to get particles to actually collide with a collision object in LW?

05-09-2008, 10:51 PM
For simple geometry I think it is easy to use a collision object set to plane, box or whatever rather than use object geometry.

But here is a simple test scene. I did not set it to Stick only upped the Friction power to 1000.

05-10-2008, 08:46 AM
Thank you, Surrealist. I didn't think of using bounce mode plus lots of friction. I did try friction with stick mode, but the particles simply reacted by calculating the same motion more slowly.

When I set bounce and friction, the first run through resulted in my particles all bouncing off my surface. So I copied all your exact settings, then changed the fewest to make it work with my scene.

It's plain that particles can't accurately collide with objects. Not for me. Not today. I suppose I could assemble my object out of small collision boxes, but I'm afraid collision boxes would stop working for me if I tried that.

I'll just do some other animation. Thanks for your effort!

05-10-2008, 09:25 AM
Can't you use your object and the collision? Guess I am not sure of the effect bu the collision can co-exist with the actual object, if that helps at all.

05-10-2008, 05:10 PM
My object is a displaced subdivided plane. The idea was to reveal the cool surface shape with motionless particles stuck to it. So the object needed to be the collision item.

05-10-2008, 07:18 PM

Every time this happens I think to myself. "Why don't I ask what the intended effect is first..............."

There may be a better way to do that I think. The object as an emitter set to points? I don't know, just an idea. Not sure how it treats the subD displaced mesh though. (which might be part of your problem) But you could adjust the birthrate and vel so they only appear.

In any case there has got to be a way to do that.

Mr Rid
05-11-2008, 03:34 AM
'Stick' should work. Did you click the 'Calculate' button?

05-11-2008, 06:59 AM
Dang. That worked great. How do I upload one of those scene download thingies like Surrealist did in post #2? I'll show you what happens when I try it.

05-11-2008, 07:33 AM
Get yourself a free copy of 7 zip (http://www.7-zip.org/)

After you install it, right click on the file and choose 7zip then in Add to archive the 7zip panel set the archive format to zip. I usually leave everything else at the default. It will create a zip folder right there in the same folder and you can upload that. And dang indeed, how daft of the both of us. :)

05-11-2008, 07:43 AM
Okay, here's a test.

I've made an object and given it a sticky collision with 5000 friction power.

The vast majority of the particles pass through the smaller, triangulated part of the mesh. (Oddly, some particles stick to the back-facing polys after they pass through the object.)

The larger quads seem to capture 100% of the particles. That's a surprise. I would have thought that those large areas would represent more potential 'holes' for the particles to slip through. Live and learn.

Also, giving the particles some nonzero size seems to help.

05-11-2008, 11:31 AM
OK I like the Collision object set to Bounce myself. I used a friction power of 1,000 and a bounce of 100.

For the emitter I changed the Particle size to [.003]. This keeps them from falling through. Then for kicks I widened it to 300mm on the Z and set the birthrate to 500 and the limit to 10,000.

Not sure of the effect you want on the particles but I thought it looked cool with more. Depends on what you use for the particles I guess.

This gets you in the ballpark and you can tweak it from there.

And as a note setting it to Stick is cool, but I guess it takes more particles since they stick to it in 3D. And that might be a nicer effect for you. it depends.