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I am looking for a way to create a very long cylindrical object that maintains a specific length (and volume/radius) at all times.

But I want to be able to deform that object by bending it, and looping it, and so forth.

Basically a piece of string is what I'm trying to model. I want the string to be X units in length. But I want to be able to pick it up from the middle, or the end, or loop it or even tie it up. And have it remain the same length.

Is there any way to to do this in blender? To manipulate an objects shape, but keeping some of its basic physical size constant?

Nertskull
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If you are looking for a mathematically perfect solution that keeps the exact length and volume of the geometry then I don't know how to achieve that. AS far as I know Blender might not even be the right tool for that job.

For a relatively accurate from a visual point of view you may use the usial Array + Curve modifier duo.

Just model a small cylinder-shaped section of your string (or whatever detaild shape you want to have) and add an Array with a fixed count of items, this will ensure the length is kept approximately constant.

On top of it add a Curve modifier, that will deform it so you can controll bending and knots without affecting length too much.

enter image description here

Bending will however affect lenght and the distortions will inevitable change the volume, but visually it will roughly behave as a tring

Duarte Farrajota Ramos
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  • That was a great thought, and after playing around for a while it kind of got me there. But when you start making tight corners it actually can change the length a fair amount. – Nertskull Jun 30 '17 at 11:28
  • Yes, tight curvatures will make the inaccuracy of the method more apparent. Adding shorter cylinder segments will minimize it at the expense of performance, but as curvature gets closer to the cylinder radius volume loss will get worse. – Duarte Farrajota Ramos Jun 30 '17 at 15:56