Help with RB+SB

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BrianLooney
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Help with RB+SB

Postby BrianLooney » Fri Jan 22, 2010 3:20 pm

Hello,
So far I have only done very simple RB dynamics. My next project involves RB and SB both interacting. Here is my question: What is the best way to set up 2 rigid bodies connected by a "nylon string"? Like this: 0~0 Through reading through the help files, I noticed that using a rope constraint will simulate correctly but I don't know how to translate it's movement to a modeled string mesh. Would it be better to model the string and turn it to soft body? If so, how can I attach the two ends to the 2 rigid bodies? BTW, the whole rig will be falling onto a surface, so everything needs to have dynamic motion. I tried using a fixed constraint to fix the 2 ends of the string, but it seems that this constraint is only for working on rigid bodies? Any hints?
Brian Looney
Tulsa, Oklahoma


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bitSeq
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Help with RB+SB

Postby bitSeq » Fri Jan 22, 2010 4:04 pm

I too have had trouble with soft bodies in RF, it is very fiddly and quite often will cause a crash. I did try to attach RD's to SB's but no luck, so for that particular project I resorted to using the Havok engine in 3ds max, and my results were perfect, using the rope soft body I was able to set tensions, thickness and more.

Ta

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BrianLooney
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Help with RB+SB

Postby BrianLooney » Sat Jan 23, 2010 5:54 pm

Thanks for the answer. I didn't want to resort to the Havoc, but I guess I'll have to.
Brian Looney
Tulsa, Oklahoma

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BrianLooney
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Help with RB+SB

Postby BrianLooney » Wed Feb 10, 2010 4:39 pm

So just to make sure, there's no way to attach a soft body to a dynamically moving rigid body in RF?
Brian Looney
Tulsa, Oklahoma

Ghosteg
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Help with RB+SB

Postby Ghosteg » Wed Feb 10, 2010 4:46 pm

Bubbaloo wrote: So just to make sure, there's no way to attach a soft body to a dynamically moving rigid body in RF?

u can use the rope to attach 2 different rigid bodies using the parent and child options, but u cant grab soft body vertices and attach it to a moving rigid body. Instead u could link ur whole soft body as any other body to a rigid body using the "parent to" function in the node rollout.

shaun_michael
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Help with RB+SB

Postby shaun_michael » Wed Feb 10, 2010 4:59 pm

Ghosteg wrote: [quote=Bubbaloo]So just to make sure, there's no way to attach a soft body to a dynamically moving rigid body in RF?

u can use the rope to attach 2 different rigid bodies using the parent and child options, but u cant grab soft body vertices and attach it to a moving rigid body. Instead u could link ur whole soft body as any other body to a rigid body using the "parent to" function in the node rollout.[/quote]
Whilst that might appear to work when running a sim, setting a simple scene up would show that dynamic reactions still don't occur in the parenting relationship with a Parent Rigid>Child Soft relationship.

Give it a go. Add a rigid cube, non-motion rigid floor plane and a soft-body sphere parented to the cube. Add some gravity and sim.

Whilst the parenting seems to be working during the fall, as the cube hits the ground plane, the parenting is lost. Stop the sim though, and rotate the cube around and presto, it appears that the link is still active. As the cube is tumbling after collision, select the sphere and you'll see it's locator is attached to the cube, but it's dynamics are free.

I'd like to be proved wrong though.

Shaun

Ghosteg
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Help with RB+SB

Postby Ghosteg » Wed Feb 10, 2010 5:54 pm

shaun_michael wrote: [quote=Ghosteg][quote=Bubbaloo]So just to make sure, there's no way to attach a soft body to a dynamically moving rigid body in RF?

u can use the rope to attach 2 different rigid bodies using the parent and child options, but u cant grab soft body vertices and attach it to a moving rigid body. Instead u could link ur whole soft body as any other body to a rigid body using the "parent to" function in the node rollout.[/quote]
Whilst that might appear to work when running a sim, setting a simple scene up would show that dynamic reactions still don't occur in the parenting relationship with a Parent Rigid>Child Soft relationship.

Give it a go. Add a rigid cube, non-motion rigid floor plane and a soft-body sphere parented to the cube. Add some gravity and sim.

Whilst the parenting seems to be working during the fall, as the cube hits the ground plane, the parenting is lost. Stop the sim though, and rotate the cube around and presto, it appears that the link is still active. As the cube is tumbling after collision, select the sphere and you'll see it's locator is attached to the cube, but it's dynamics are free.

I'd like to be proved wrong though.

Shaun[/quote]
yeah i agree with you fully, after collision, dynamics override any existing parent>child link made in the node rollout but i thaught that's what he asked about, if it's possible to attach a soft body to a rigid one. Maybe Bubbaloo needs only a soft body position driven at the beginning by a rigid body :). Instead, the parent>child link can be broken of left unbreakable in the constraint's options if that type of link is used (not the "parent to" from the node rollout)

shaun_michael
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Help with RB+SB

Postby shaun_michael » Wed Feb 10, 2010 6:04 pm

I don't think you can use a soft body as the child in a constraint relationship though, I'm pretty sure it needs to be a rigid body, but as you say, maybe the requirement is just that ordinary parent<>child relationship at the beginning.

Shaun

Ghosteg
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Help with RB+SB

Postby Ghosteg » Wed Feb 10, 2010 6:13 pm

shaun_michael wrote: I don't think you can use a soft body as the child in a constraint relationship though, I'm pretty sure it needs to be a rigid body, but as you say, maybe the requirement is just that ordinary parent<>child relationship at the beginning.

Shaun

I'm at work now, so i tried directly into my wip scene)... constraints work with soft bodies like with any other rigid bodies)

shaun_michael
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Help with RB+SB

Postby shaun_michael » Wed Feb 10, 2010 7:36 pm

Hmmm, interesting. I get an error every time I try to attach an object with softbody dynamics enabled as a child of a constraint - "Selected object doesn't have the dynamics properly enabled" - meaning its not a rigid body.

This hint in the docs seems to suggest something regarding the limitation of constraints:-
Hint: Remember constraints only have sense in a dynamic environment, so do not forget to set the Dynamics property to Rigid Body in the objects' node.

Care to share?

Shaun


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