Folding triangles - hinging problem


(Ariadna Plescan) #1

Hello,
I am currently trying to figure out how to use an ik chain in order to achieve the folding pattern of the animated cube, which was done in grasshopper. But I can’t figure out how to recreate it in bongo… more precisely I can’t managed to solve the folding of triangle 2 along the diagonal BD and get the pivot to rotate along the diagonal, which I set to be one of the pivot axis. I made triangle 2 a child of triangle 1, part of an IK chain - Joint and constraint, Type: Hinge - set the rotation axis - but when animated triangle 2 does not fold along the diagonal BD as triangle 1 folds into place. I would be grateful for any suggestions in how I should approach the problem. The folding mechanism of the cube is part of more complex model, with moving parts which I can’t recreate in grasshopper. This is why I would like to solve it with Bongo.
Best regards,
Ariadna


(Luc Adriaenssen) #2

Hi Ariadna,

I guess you have a set up like this.
Naamloos

In order to make an object rotate along its pivot’s axis (Forward or Inverse Kinematics) the “Rotate in world space” option in Bongo’s object settings must be unmarked.
Untitled-1
If not the object keeps rotating along the world axis no matter how the pivot is twisted or turned (a leftover from Bongo 1).

Luc


(Ariadna Plescan) #3

Dear Luc,
Thank you very much for your fast and accurate reply, I would not have guessed that setting on my own. I will probably return with more questions.
Best regards,
Ariadna


(Luc Adriaenssen) #4

Ariadna,

Your welcome. Also with further questions.

But I want to save you the annoyance and disappointment over your own inability to deal with Bongo’s IK or over the inability of Bongo’s IK to cope with this model.
In my humble opinion a cube like such composed with hinging rigid triangles cannot fold at all. It is stiff.
Try to make one in cardboard and you’ll see.

Luc


(Ariadna Plescan) #5

Hello Luc,
Actually this is a folding pattern, called Kresling pattern. In paper models it’s ideal to test. A great variety of polygonal shapes are possible. With thicker materials it also works depending on the hinging method used. I have tested it with different materials.




(Luc Adriaenssen) #6

Thans for the info Ariadna,

I still have strong doubts, but eh… it’s your project.
Just wanted to warn, not to easily to blame Bongo’s IK for malfunctioning. It’s computer logic – it does not ‘deflect’ - hinging is hinging – there is no ‘kind of’.
When Rhino seems to freeze (not responding … and “Escape” (like the commandline recommends) doesn’t do a thing) the IK solver is probably working its brains out to find an unfindable solution. Just be patient. It can take some minutes… but it will regain consciousness.

Luc


#7

It doesn’t look like an easy one this. :thinking:

The “opening” may have to be forcefully rotated in order to get it right. I only get this far, but perhaps making the rear corners into universal joints as to allow the “backplane” to skew in order to give more freedom to the sides during the rotation.

Folded Cube 002.3dm (131.9 KB)

:slight_smile:

// Rolf


(Luc Adriaenssen) #8

Hi Rolf,

Still enjoying a remarkable IK-puzzle, aren’t you? :wink:

Indeed rotation of the “opening” I think is the best way to drive the IK-chain. In the attached model I set the rotating opening free to move back and forth in accordance to its bindings.

Folding 001.3dm (73.9 KB)

As you can see the orthogonal ribs force the front to make a movement different from the diagonal connection.

Joining them into 1 object makes folding impossible.
In the images of the cube Ariadna shows above the “hinges” are made with snap locks. Probably such gives sufficient suppleness to deal with the dissimilarity. But then again Bongo does not offer “wobbly” hinges.

I did make a cardboard model and indeed … it does not fold.
Luc


#9

I’m absolutely thrilled!

I kept trying after I posted, including the “diagonal only” approach, and if I had succeded I had posted again. But I didn’t. Post. :wink:

// Rolf