NOOB: Catching a ball using a cloth.

[hopbin9]

Hi,

I'm having a problem doing something simple. Catching a ball using a piece of cloth.

Here are my steps.

- create a sphere, and grid. Raise the sphere above the grid.

- make the grid a cloth, and pin all four corners.

- make the sphere a RBD object.

When I play the sim the sphere falls, hits the cloth and stretches it but keeps on falling until it passes threw the cloth. It appears that the cloth does not slow down the sphere.

I tried increasing the strength of the stretchiness, but this only slows down the sim and the sphere isn't stopped by the cloth.

What could I be doing wrong?

Thanks,

[hopbin9]

I found this thread on sidefx regarding the issue.

SideFx Cloth Discussion

So it appears that RBD-To-Cloth is supported, but Cloth-To-RBD is not supported. Even in Houdini 10.x (didn't see anything in the release notes for 11 to suggest this has been resolved).

A work around recommended was to make the RBD object a cloth object using the bend model of "strong" and no stretching. I tried this, and it does appear to be working but I can strange resolves.

The sphere bounces back, retains it's sphere shape, but it starts spinning wildly when it settles into the cloth surface. It starts rolling across the cloth until it falls over the edge. I'm not sure what's causing it, but adjusting some more settings might resolve it.

[hopbin9]

I got it working

Seems that if the sphere had to much mass it would start behaving strangely. With more friction and a lighter sphere it now lands and rolls into the center of the grid. I'm going to try something more complex with about 9 spheres.

Not high tech sim work, but at least I was able to figure it out on my own. (Not such a noob after all). lol

Edited September 7, 2010 by hopbin9

[hopbin9]

Here's a sample image of what I managed today. Going to render out of a video later.

I spent some time trying to understand more about VEX shaders, and how they work. Anyone recommend some good VEX shader tutorials?

Thanks,

[hopbin9]

Can anyone give me a quick tip on how to get tearing to work?

Is it as simple as turning on tearing in the cloth solver, or does it require some kind of SOP to break up the cloth (i.e. like in fracturing).

[hopbin9]

Everything is new for me as I continue to learn more of the Houdini way of things. Struggled last night to understand VEX shaders and why Houdini works this way. Seems to me I prefer to have a material editor that was graph based. Found it strange that you have to almost program your own shaders every time you want to use a procedural texture. I'm hoping I'll learn more after completing the digital tutorials course on rendering Houdini, but I don't understand why we can't define texture networks at the SHOP level. Would seem that VEX is for the math stuff, and SHOP should be for the creative stuff.

Did my first stamping today to change the size/color of the spheres. That is one cool feature and I can see why it's so popular.

Here's a rendering, but it took almost 15 minutes to complete on my i7 950 with 12GB. I've use to working with vray and it seems to me that Mantra is really slow. I also find it's lacking options for changing aliasing methods (or I'm just not seeing it).

[anakin78z]

Hey,

So I didn't quite understand from your posts... did you end up converting the spheres to cloth objects, or did you get it to work as rbds?

Thanks,

-z

Edited September 9, 2010 by anakin78z

[hopbin9]

I ended up converting the spheres to cloth objects, and setting the bend method to strong. There are still cases were on hard impacts the spheres will deform and bounce back into sphere shapes, but increasing the stiffness of the cloth would fix that problem. The only problem with this method is that calculation times are higher for cloth then RBD. I also found that you need to make the mesh of the spheres a little higher resolution then you would have used with RBD.

My next experiments will be with causing tearing effects when the spheres impact. I was thinking of creating a box and having spheres smash threw the box. Hopefully when they impact the first side of a box the tearing effect will deflect the sphere and cause it to come out on a different angle from within the box. (hard to explain, but I'll post a video when it's done).

I've attached the HIP, but I was also playing around with VEX so let me know if it has any problems loading.

ball-to-cloth.hip