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jaxtone
08-12-2014, 11:46 PM
Any one who knows how I can attract an object with multiple forces in Bullet?

In this video I guessed most of youīve already seen there are many bullets that deforms and crash an object!

Can this be done in Bullet Dynamics and if so, how?

https://www.youtube.com/watch?v=J9HaT23b-xc

ncr100
08-13-2014, 12:39 AM
Here's a good example (NOT MINE):
https://www.youtube.com/watch?v=PS4FLL8a1NU

Mine is attached - 15m to make, and the planks jitter at the beginning.
123618

123619

Q: what do you mean attract forces?

Greenlaw
08-13-2014, 03:28 AM
Not sure what you mean either but I sometimes invert a force's strength to create an 'attraction' effect. For example, in the Brudders' excerpt (https://vimeo.com/channels/littlegreendog/68543424) we posted last year, I used a Vortex force to spin leaves around the center of the cemetery and an Explosion force with a negative value to draw the leaves inward and hold them inside the cyclone. It's not really attraction but, as in this case, the trick can resembles it. You could us a variation of this technique to make structures collapse inward, like in a carefully controlled building demolition.

prometheus
08-13-2014, 10:04 AM
not sure either what you are after Jaxtone?...here is another example of collisions, but not with forces specificly, though it can be done eqally I think as Greenlaw mentioned with vortex forces, here I used traditional old wind dynamics to push standard particles..the particles are fx_linked and cloned together with a null that is a kinematic force, so when each particle hits the bullet brick wall, it destroys it thanks to the kinematic force applied and cloned on each particle.

Looking forward to see if the lightwave team can introduce interoperability with bullet soon, just as modo can do today, then we wouldnīt need to go this route, instead simply use particle weight and size to set the collision area and strength.


http://www.youtube.com/watch?v=PSd5iN3ZWG0&list=UUDxRvcWi0V7RgW69O5Ax5Og

jaxtone
08-13-2014, 12:52 PM
prometheus! That was a very nice scenery... great to see that many attractors can demolish an object. How was that done? Itīs ok if you donīt wanna share but I am really curious of what can be done with Bullet dynamics!

I add some pictures to describe the scene I wanīt to create to see if you or anyone can explain how to do it right. The mad thing is that Bullet seems to work from time to time but suddenly all information about dynamics and attractions have dissappeared. But if I change some pointless setting with a small amount it all start to work again. I am new to Bullet but must ask if this is a well know bug within it?

Another thing is that the platform starts to fall down as soon as I start the scene unless I set the gravity to Zero. I just want the demolished parts of the platform to fall downwards when the attractor hits it! Maybe thereīs another way to lock an object in itīs position before the hit. (I could as well put an invisible groundplate under each platform but it feels so 90īs to do that :)

ncr100
08-13-2014, 02:03 PM
Maybe try keyframe activation not sleep?

prometheus
08-13-2014, 02:16 PM
prometheus! That was a very nice scenery... great to see that many attractors can demolish an object. How was that done? Itīs ok if you donīt wanna share but I am really curious of what can be done with Bullet dynamics!

I add some pictures to describe the scene I wanīt to create to see if you or anyone can explain how to do it right. The mad thing is that Bullet seems to work from time to time but suddenly all information about dynamics and attractions have dissappeared. But if I change some pointless setting with a small amount it all start to work again. I am new to Bullet but must ask if this is a well know bug within it?

Another thing is that the platform starts to fall down as soon as I start the scene unless I set the gravity to Zero. I just want the demolished parts of the platform to fall downwards when the attractor hits it! Maybe thereīs another way to lock an object in itīs position before the hit. (I could as well put an invisible groundplate under each platform but it feels so 90īs to do that :)

will look in to what you have in mind later, as for how I set it up, well...simply add a null and activate it as kinematic object in the bullet tab, add particle emitter and use the fx linker to clone_replace particle to that of the null kinematic object, and it should work, well it sounds simple to me, but I reckon I have to do a simple vid showcase or something, even without sound...for a starter.

Itīs just basic similar stuff as if you replace_clone particles with objects, but in this case with a single null that is made kinematic, you just have to match fx linker clones amount to that of the particle amount, you can even particle fx clone parts objects,rigid objects etc..but those are often attributed with initial other forces making them not working so good by default, that is following the particles correctly.

you would also preferably set a gradient size based on distance to the null kinematic, to control the collison size...canīt recall exactly though and I have to reload the scenes and check it again.
mind that it was only the main 6 particles( particle carrier that has a cloned kinematic null object) the particle trails are not working dynamicly with bullet.

as ncr100 mentioned, set keyframe activation to sleep, so it wont have any gravity effect until it is colliding with something.

for your foot step cracking ground, I would simply parent a null to some bone, and make sure the null is activated as kinematic, and make a gradient with distance to null to control the collision size.
I did something like that having a daz figures boxing and the hand smashing in to a wall and breaking it.

jaxtone
08-14-2014, 03:04 AM
Thanks!

To adjust the sleep factor made it worked much better!

But how come all platforms are crashed when the first force cube are landing on platform 1?


PS. By the way I didnīt get this at all... could you please explain again...

Is the gradient you mentioned earlier supposed to be done in Modeler?

Witch of the both objects is it supposed to be attached to?



"make a gradient with distance to null to control the collision size"

prometheus
08-14-2014, 07:23 AM
doing some render testīs now, so for the moment I canīt explain much more, but you donīt set the gradient up in modeler, you set the gradient up on the kinematics tab, and I think I was misleading you too, the distance to null ...it is the same null as you
are using as a kinematic object.

and the platforms are probably reacting to the kinematic null object since it has no gradient to control the size of the kinematic impact.

hereīs something similar, canīt recall if he uses a kinematic force in there too? otherwise he is just breaking the objects by releasing the glue strength based on a gradient set up on a simple null, but here that gradient is set up within the parts that
are suppose to break and referencing the null with itīs sized/distance gradient.
http://www.youtube.com/watch?v=8MJl0LV_s5c


Iīm sorry jaxtone, think I was fooling you ...
the setup with gradients are valid on forces and on a simple null that acts like a release/solver of the glue strength.
But for kinematic object that is a simple null, I recommend to build the null with item shape in order to set your preferecd scale of the collision, once you got that right, copy that scale and paste it in the null scale value.

Might actually be easier to simply use a simple cube to get better size control.