Grid flapper

Hi all,

I’m working on a kinetic sculpture composed of an array of hanging tiles (“flappers”). I’d like to see if I can simulate their behavior when the metal grid they are attached to is perturbed. I can easily simulate a single flapper, but it’s been a while since I spent time with Kangaroo, and I’m already stuck – I can create more flappers, but can’t figure out how to get them to move independently. Any input appreciated! (13.7 KB)

sorry - no contribution to the .gh file / solution.

but I checkt the video link and it reminds me on this project:

Technorama Facade, 2002, Ned Kahn
The Swiss Science Center, Winterthur, Switzerland

Indeed – Ned is a friend and neighbor, and I’m working with him on possible in-home versions of some of his work. Here he is in his studio, demo’ing this piece.

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blender style (43.4 KB)

Not K2 and need plugins.
Honeycam 2023-05-07 11-44-45


Thank you for this! It’s very interesting, and a valuable tool for emulating the look of wind-driven flapper arrays (and no doubt, fields of long grass). But my interest is in understanding how the array behaves when the grid (scaffold) is perturbed periodically – at various frequencies and from different locations along the grid’s edge. I suspect the grid itself exhibits the same modes of vibration that describe thin plates:

I chose K2 because it’s been extremely helpful (great thanks to @DanielPiker) for simulating several of my other kinetic projects, and at times provides insights I had not gleaned from my empiric trials. I’m hoping to find “aesthetic phenomena” emerge “naturally” from the physics of the model.

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I’ve continued to play with this simulation, and though far from ideal, have gotten it to where it may be useful for the project (it definitely added to my familiarity with parts of K2).

Thinking that a grid mesh would be a good fit for emulating the metal grid, I tried that first but couldn’t get it to behave like the real thing. So I turned to using warp and weft arrays of rods, sharing vertex positions where the rods cross, akin to the steel grid’s welds. This at least appears to behave better. Given my rudimentary understanding of how K2 works (verts are masses and lines between them are springs) I’m curious, @DanielPiker, how is a grid mesh different than a warp / weft rod assembly welded at intersections?
grid3 and (33.0 KB)

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Hi @Bruce_Shapiro
Sorry I hadn’t taken a proper look at this earlier - it’s a fascinating piece.

To answer your question - a square grid of just length constraints will behave like each edge is a separate rod, connected with pin joints at the vertices free to swivel and rotate in any direction.

If instead the edges are joined into polylines in the warp and weft directions and used in a Rod goal, it’s like having continuous rods in each direction, connected to each other with pin joints where they cross. The angle of each segment with the connected ones in the same direction is restricted (i.e. bending along each rod), but all the other degrees of freedom are still free (so for instance there is nothing resisting the quads becoming diamond shaped).

I think you are right that the grid itself will be essentially moving with the vibration modes of a plate (since it looks welded and all degrees of freedom at the nodes are constrained), and the secondary motion of the flaps comes from the interaction of this motion with the flap acting as a driven pendulum.

I’ll have a think about how simplest to simulate this. I think because the deformations of the grid are relatively small, they can probably be well approximated by 1d motion at each point normal to the plane of the grid.


Here’s a first go at it. (25.9 KB)


Awesome work Daniel! And no need to apologize. In retrospect, I’m glad you missed the first post. Had you posted your solution immediately I would not have been forced to learn as much as I did by trial and error on my own. And now I get to learn so much more by going through every piece of your definition and absorbing the economy and concision of your choices. Sincere thanks!

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