Grasshopper

algorithmic modeling for Rhino

Dear Daniel (et al.)

Just for fun, I tried modelling this beautiful clock design by Matthew Gilbert in K2:

https://vimeo.com/180492315

Unfortunately, when the structure is peturbed in my own model I can't seem to maintain the bending resistance of the short three-point polylines using the rod component in K2:

They seem to resist no bending at all, although the structure (as constrained in the video and in the attached definition) should have only 1 DOF.

Please find attached definition, and any help and advice is appreciated. I seem to get this running in K1 with the 'rod' userobject equivalent, but not in K2. It's probably user error of course, but would be nice to find out!

Thanks in advance,

John.

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Hey John,

Two things jump out:

Relationship of scale - the elements in your model are quite large compared to the default strengths. Daniel would be able to provide a better explanation of why that affects things than I can. But I got better results by bumping up axial and bending strength and scaling the whole model to 0.1 of itself.

More importantly - I think your model is actually overconstrained so it can't move as you want. The pairs of members that form a single rigid part need to have the same length to work and your ones don't, the outer ones are in fact longer, which locks the whole system in place. So I fixed that and got the below:

Also it was an opportunity to play with Dan's new rigid point groups goal. Which seems to allow even more stability and faster movement in this situation.

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John, 

I'm a fan of Kangaroo, however I would solve this problem with an equation. 

Basically you have to define the side length of the quad, length of the hand and length of a link. 

This results in a inner radius.

From there it's a bit of trigonometry and you get the other two radii.

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Hi John,

simply constrain the angle of 2 groups rods and give some 1-DOF anchors, if you want let it rocks by applying a wave function!

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