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MrGAG

"up" like balloons setup

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Hi everyone, I am currently trying go a dig a little deeper into DOPs. They have always scared me a little.

I used a hip file I found on this forum to understand the "apply relationship" Dop. It was very usefull: I have been able to attach a bunch of balloons to some wires pinned to the ground.

The problem is that when the balloons go up in the air, wires are stretched out , applying no resistance at all to the ballons ( they just continu to rise up)

I can't figure out a way to build objects relationships so that my wires affect the balloons.

I hope it's clear

I've attached a hip file.

applyrelationship_concept_01.hip

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"balloons on a string" has been a topic discussed here a few times. I've tried to do it myself a few times, but couldn't get it work.

The DOP network does not support force feedback effects. So things like cloth, constraints and fluids don't feed back forces to RBD that cause circular dependencies. I don't know if that's a good description of the problem, but it's the best way I can think of to describe it.

There is a tutorial in the manual that demonstrates a "hack" to get around this limitation, but it's a complicated process. It's called "popswithrbdcollision". While it shows how to do something unrelated to your setup. It does show how to copy forces from the RBD object to somewhere else, and then have it feed back into the RBD object again. It does this by taking the forces already calculated on the previous frame (which I think solves the circular dependencies problem).

So to do the "balloons on a string". You would need two balloon objects. One that would a RBD responding to the up force, and another driving the pin constraint. You'd need to copy forces between to the two balloons to make it work.

I can picture how it would work in my head, but I haven't had the time to give it a try :)

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hi, thank you for your reply.

I had no idea houdini had such a "limitation". I would have become crazy trying to make it work. :blink:

I will take a look a this "hack" example file.

thanks again :)

Edited by MrGAG

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yeah .... the "popswithrbdcollision" example is a pretty scary one :unsure:

I guess I need to get more comfortable with Dops before digging into this kind of solution.

And I am not even mentionning the fact that I wouldn't know how to adapt this to solve my balloons problem to begin with ;)

Still, I am kind of surprised see that houdini's dynamic engine has some sort of " limitations " !! I thought it could simulate the entire world :P

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Still, I am kind of surprised see that houdini's dynamic engine has some sort of " limitations " !! I thought it could simulate the entire world :P

lol, that's what I thought when I discovered this.

Give it some time. The ability to resolve this kind of problems in Houdini will separate you from the pros and hobbyists ;)

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Hi everyone, I am currently trying go a dig a little deeper into DOPs. They have always scared me a little.

I used a hip file I found on this forum to understand the "apply relationship" Dop. It was very usefull: I have been able to attach a bunch of balloons to some wires pinned to the ground.

The problem is that when the balloons go up in the air, wires are stretched out , applying no resistance at all to the ballons ( they just continu to rise up)

I can't figure out a way to build objects relationships so that my wires affect the balloons.

I hope it's clear

I've attached a hip file.

Create another constraint relation with ballons spring-constrainted to the wire root point.

Either with another relation in same applyrel node and some stamping.

Or like in my example with two constraint nodes.

2Constraints.hipnc

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That's a clever approach.

I'd like to do something where the wire was done as cloth, with wire-to-wire collision driving soft bodies of balloons colliding. Not sure if a collection of springs would give realistic results.

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clever approach indeed :) , I didn't think of that.

it's doing the trick already !

I'll post a hip file soon

thank you

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@Guillaume

 

now you had 3 years time :D can you post the hip file now?

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the new pops in dops can help, as the pop forces can be used with rbd objects, even rbd packed objects

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