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View Full Version : ClothFX problem: hold-structure & gravity



serge
05-18-2005, 12:10 PM
LW 8.3.

I created a ball. Applied dynamic --> ClothFX. Applied preset --> jelly. Applied gravity --> Y=-10m. And pressed calculate.

The ball falls during the first few frames, then stops and keeps on wiggling in the air. I found out that if I set hold-structure to '0' the ball just falls as expected. If I apply a value of hold-structure bigger than '0' the ball stops somewhere in the air. And the higher the value of hold-structure, the sooner the ball stops from falling down.

There has to be some way to correct this, otherwise how can one make falling jelly!! :D

Dodgy
05-18-2005, 01:19 PM
Ahhhhh I will now teach you one of the secrets of the universe young grasshopper!

EITHER use the Object>pressure effect setting (a setting of 30 or so is good) in Motion Designer, which attempts to keep your object solid

OR Add HardFx to your object first, and then ClothFx with a decent hold Structure value. What this does is make the object fall under Hard dynamics, then the object tries to stay with it in a soft way. It's a fiddle, but it works pretty well.

OR add in some polys which connect together the faces within your object and use these to keep it rigid (this is how the majority of soft bodies work, by adding connecting springs inside the object) I may have a go at writing a spring adding plugin since this would be quite handy.

The HardFX route is usually the way I go since it's quite quick to set up and is quite convincing.

We could really do with a pressure effect setting for

serge
05-18-2005, 03:40 PM
Thank you master. :)

Few questions though:

1: Where do I find "Object>pressure effect setting in Motion Designer". Or did you by any chance mean "spring" value in ClothFX? If so, adjusting this value doesn't solve my problem.

2: Yes, adding HardFX before ClothFX (and adding gravity within HardFX) let's the ball fall all the way down. However, it does look far from realistic (I'm using a collision object as well), so I guess I'll have to tweak here and there. We'll see....

3: About your suggestion "add in some polys which connect together the faces within your object": Is this an alternative for using ClothFX --> jelly preset? I don't really understand. What settings would I have to use then in Motion Designer?

4: And the most important question: What is the reason that the object loses it's gravity with the settings I described above? Can you give me a logical explanation for that, since I would like to understand how Motion Designer works exactly. Again, my object does fall down, but suddenly stops during the fall due to 'hold-structure' value.

Dodgy
05-18-2005, 04:42 PM
1: Where do I find "Object>pressure effect setting in Motion Designer". Or did you by any chance mean "spring" value in ClothFX? If so, adjusting this value doesn't solve my problem.


It's not in the surface section, it's in the Object section, where you first Activate your object.


2: Yes, adding HardFX before ClothFX (and adding gravity within HardFX) let's the ball fall all the way down. However, it does look far from realistic (I'm using a collision object as well), so I guess I'll have to tweak here and there. We'll see....

This does work, it does require tweaking though to get it looking real.


3: About your suggestion "add in some polys which connect together the faces within your object": Is this an alternative for using ClothFX --> jelly preset? I don't really understand. What settings would I have to use then in Motion Designer?

4: And the most important question: What is the reason that the object loses it's gravity with the settings I described above? Can you give me a logical explanation for that, since I would like to understand how Motion Designer works exactly. Again, my object does fall down, but suddenly stops during the fall due to 'hold-structure' value.

Hold structure basically always tries to get the object's vertices to where they are when undeformed, so this pulls them up and doesn't play well with gravity, this is why Hardfx works. The Jelly preset bumps up the Hold structure value, so it does the same.

Adding the connecting polys just adds a substructure within your object. Upping the Substructure value only increases the strength between vertices along edges, so hollow balls will go flat (you can decrease this a little by bumping up the compress stress, but even that won't stop it really going somewhat flat and it'll probably explode first). However if you put in the poly struts, these will try to remain the same length, and so keep the object rigid. This is how alot of Soft body simulators try to do this sort of thing, and will give the most realistic results, but is a pain in the butt to set up, hence my thought that an Lscript would be most useful for this..

serge
05-18-2005, 05:16 PM
Dodgy, thanks a lot. :)


It's not in the surface section, it's in the Object section, where you first Activate your object.


Hmm, I didn't even know there was someting like "activating" my object. You mean through MD-controller or not? Is this necessary, since the manual says that MD-controller "is a legacy tool that has been replaced with Lightwave's dynamics tools and is available for use with older scene files". You see, I'm a beginner who tries to find out more about dynamics. So I started at the dynamics chapter in the manual. There isn't any notice of "activating an object". :confused:

Dodgy
05-18-2005, 06:20 PM
Activating an object in Motion Designer basically making it a Soft Object. This is done in the MD Property panel, which you can pull up using the MD Controller panel. It's the panel which has all the settings for your objects in it.

On the other hand, by cranking up the Spring/Sub Structure and Compress Stress settings to over 1000, you can get some objects to keep inflated. I've been messing about with this and it is sensitive, but it can be done.

serge
05-18-2005, 06:54 PM
Activating an object in Motion Designer basically making it a Soft Object. This is done in the MD Property panel, which you can pull up using the MD Controller panel. It's the panel which has all the settings for your objects in it
Yes, but is MD-controller (and activating an object through MD-controller) still necessary in LW8?

serge
05-19-2005, 09:52 AM
So, if I may summarize:

Although there are workarounds to achieve reasonable results, the problem I described can be considered a bug/failure in Lightwave, right? Applying hold-structure to an object shouldn't keep it from falling down when gravity applied.

Dodgy
05-19-2005, 10:26 AM
I think possibly an oversight. As it is, it can be used for making flesh parts wobble on a character, without the whole character falling down.

The best thing would be to make a feature request :)