Do you wanna build a snowman? (I do, but I have some questions...)

[tyFlow]

Hey,

I´m just starting to play around with tyFlow, which is just sooo much fun, figuring out all the cool new stuff I can do within Max...

After just "doodling" for a while with that warm fuzzy feeling in my tummy only tyFlow or true love can give you...
I decided to go into it a bit deeper and see what I don´t get.

So here is my first in depth trial, destroying a snowman:



And here is the flow:




A couple of questions:

2. I´m trying to make the snow stickier, so it breaks off in bigger chunks. I increased the steps in the tyFlows "particle Bind solver" to 50 and higher, but its still not sticky enough. And when increase steps above 50, after a certain point it looks like there are particles disappearing. So, how do I make it stickier? There are a couple more settings in different places I´m considering:
A) "Stiffness" in the particle Bind operator
B) "Stretch" in the particle Bind operator under "Break"
C) "Stiffness" in the particle physics operator under "Collision force".
3.  Does it make a difference in for the voxelisation, if I just stack three spheres on top of each other, or if I create a connected, closed mesh?
4. Right now the collision sphere is just crudely hand animated.
Ideally I´d like it to be a dynamic rigid body, interacting with the snowman. How do I generally go about this kind of setup? (one flow interacting with another one)

Hey nice test!

I want the grains not to react to gravity, before the sphere hits it. I put the sphere as a collider in the birth even, added a physxSwitch and set it to dynamic sleep (and also tried kinematic) and then in the second event I set it to dynamic wake. But gravity still starts in the first event. What am I doing wrong here?

The PhysX operators are only compatible with the PhysX solver. Mixing Particle Bind operators and PhysX operators won't work the way you're intending.

You do pose an interesting question though....how to allow particles to remain static until triggered by something, like a collider? It's actually not an easy question to answer for a variety of reasons. For example, when the snowball hits the head of the snowman, you'd normally want the reverberations of the impact to affect the entire snowman, as he breaks and falls apart...but how does a particle at the base of the snowman know that a particle in his head was hit by something? Somehow they have to communicate.

Currently, you could try adjusting the sleep settings in the Particle Bind Solver rollout. Make it sliiiightly greater than the strength of your gravity. This should cause particles to sleep until moved by a force greater than gravity itself - ie, the snowballs. The particle will fall asleep again if their velocity goes under that threshold, but you can keyframe that value in case you don't want sleeping to come on so strongly after the impact.

I´m trying to make the snow stickier, so it breaks off in bigger chunks

Creating chunking effects like that can be done in a variety of ways. The most effective is probably using a particle clustering workflow. Basically, you create a Cluster operator and adjust the settings so that particles are grouped into smallish "clusters". Then, you have two Particle Bind operators....one that binds particles in the same cluster with strong and hard-to-break bindings. And one that binds particles in non-same clusters with weak and easy-to-break bindings. The Particle Bind operator contains cluster settings for specifically this purpose.  The overall idea is that as binds break due to strong forces acting on them (like an impact), the clustered chunks maintain most of their shape while the bonds between the chunks break faster, giving a more chunky look to the sim.

For a material like snow, you can also enable cohesion forces in your Particle Physics operator....keep the value verrrry small, but it will cause particles to slightly stract and cohere to each other...similar to wet snow or sand. You'll have to experiment a bit to get the right look.

Eventually I'll add some example files showing how to do this.

Does it make a difference in for the voxelisation, if I just stack three spheres on top of each other, or if I create a connected, closed mesh?

Nope, the Birth Voxels operator should prevent overlap even between multiple voxelized objects (there's a checkbox for that in the settings).

Ideally I´d like it to be a dynamic rigid body, interacting with the snowman. How do I generally go about this kind of setup? (one flow interacting with another one)

You could either make your snowball a part of the Particle Physics sim (which is probably what you'd want...so it has the potential to break up as well), or simulate everything in a separate flow, set that flow to have a mesh and then import it as a collider in your snowman flow.