Vellum Force by Orientation or nearby Normal

[dubCUT]

Hello

As a Houdini noob i would appreciate any comments or hints on this:

How can i apply a force for every balloon pulling against the direction of its string?

I'm sorry for the messy setup, i'm still learning a lot. (i wasn't even capable of going the "for each" route to setup the initial state of the geometry...)

 

BalloonTree.hipnc

Edited April 27, 2021 by dubCUT

[dubCUT]

so i figured out how to calculate a Force Direction Vetor for those balls points.

right what i was looking for.

but it still is not working as expected.

do i miss something obvious in the force VEXpression?

 

i even tried this:

force = set(@ForceDirx,@ForceDiry,@ForceDirz);

But the force values stay at 0.

Edited April 28, 2021 by dubCUT

[underscoreus]

I'm not entirely sure what your issue is since I don't specifically know what "not working as expected" means but I'll just write out some guesses/general thoughts.
Can't guarantee that this is a problem, but I would recommend you add a "v" in front of your attribute ("v@ForceDir"), just to make sure that vex tries to read it as a vector and not just a float. Vex is ok at figuring this out with the built-in attributes like P and v etc but in my experience, it can be hit or miss when it comes to custom attributes. Another thing to note is that the second port of the vellum solver is specifically for forces, could try to plug the wind in there. Other than that it'd just be testing by multiplying the force higher and seeing if the v or force attributes on the points change at all.

Hope you figure it out!

[dubCUT]

yes, finally got it working.

the solution was to use a pop wrangle right before the popforce!

i think the Vex thingy on the pop force cannot access attributes from outside.

v@force = v@ForceDir;

as Ryan kindly describes in this post, a pop wrangle is needed in dop to access attributes.