LDraw.org Discussion Forums

Hi all,

Would it be possible to model form this part in LDCad?

Black String, Net 8 x 16 Rectangle
https://www.bricklink.com/v2/catalog/cat...only%22:0}

Using single strings, weave, and form.
Or the part as whole and form it like we would form any flexible part in LDCad?

Jaco

(2020-04-14, 14:16)Jaco van der Molen Wrote: [ -> ]Would it be possible to model form this part in LDCad?

You could use separate strings and wave them together using lots (and lots) of path points.

Or if the wanted shape is simple and only in one direction (e.g.  __/--\___  ) you could try to make a donor part for it. The donor should have one row of weaved pattern in it.


I've been thinking about a cloth like generator multiple times, but it's been very hard to setup something useful so far.

2D (sheet) like path definitions are somewhat doable as long the height differences are not so big.

But making things fold and big changes in the surface would make it much more complicated (If one wants the cloth pattern to remain consistent).

(2020-04-14, 19:25)Roland Melkert Wrote: [ -> ]Or if the wanted shape is simple and only in one direction (e.g.  __/--\___  ) you could try to make a donor part for it. The donor should have one row of weaved pattern in it.

This is what I was thinking. If the net only needs to bend in one direction.

Jaco, what use case did you need?

(2020-04-14, 19:25)Roland Melkert Wrote: [ -> ]I've been thinking about a cloth like generator multiple times, but it's been very hard to setup something useful so far.

2D (sheet) like path definitions are somewhat doable as long the height differences are not so big.

But making things fold and big changes in the surface would make it much more complicated (If one wants the cloth pattern to remain consistent).

I think the first consideration there would be value for effort—lots of Lego sets use flexible elements, but how many actually use cloth parts? (Maybe more than I'm thinking, but certainly far fewer than linear flex elements.)

That said (and speaking as someone quite ignorant of 3D modelling), how might a cloth generator work? Could it be a matter of defining the margin, or "outline", of a cloth parts using existing flex commands, then filling in the surface using something like Coverer?

You could even have different types of donor parts for different kinds of cloth edges: sharp edge (like vinyl), rough (like unfinished woven, maybe with a setting for "coarseness"), hemmed (with a sewn seam), or invisible (like the net part we're discussing here, if it were modeled as a mesh rather than individual woven strands).

But yeah, I guess getting the pattern right would be the real problem, more than calculating the shape itself…

(2020-04-14, 20:09)N. W. Perry Wrote: [ -> ]That said (and speaking as someone quite ignorant of 3D modelling), how might a cloth generator work? Could it be a matter of defining the margin, or "outline", of a cloth parts using existing flex commands, then filling in the surface using something like Coverer?

I was thinking about 'magnets', points which pull on the cloth in certain directions.

The cloth itself is a 2d grid of vertices the generator needs to keep the distance between all vertices roughly the same in order to keep the pattern realistic.

So when you pull on the center the sheet would go into a pyramid shape.

(2020-04-14, 20:15)Roland Melkert Wrote: [ -> ]I was thinking about 'magnets', points which pull on the cloth in certain directions.

The cloth itself is a 2d grid of vertices the generator needs to keep the distance between all vertices roughly the same in order to keep the pattern realistic.

So when you pull on the center the sheet would go into a pyramid shape.

Oof…yeah, then that would have lots of side-effects, because you have to maintain the correct surface area in order for the grid to remain equally spaced. Pulling up the center would then cause the edges to draw in, it would create folds that have to "hang" realistically, etc.…

My way would probably only work for simple forms, where the cloth follows the flattest path between the defined edges (which would have to be constrained to a certain length in order to maintain the surface area).

Coincidentally, this just came up as as issue on the lsynth github.  The net generator spreadsheet could be used to model that.  But you'd have to do it in 2 parts, and you might want to substitute string parts for the box primatives.  There's a link to the net generator download somewhere in the issue messages.  https://github.com/deeice/lsynth/issues/5

(2020-04-14, 19:48)Orion Pobursky Wrote: [ -> ]This is what I was thinking. If the net only needs to bend in one direction.

Jaco, what use case did you need?

I was trying to model something like this:
[attachment=5100]

(2020-04-15, 0:16)Don Heyse Wrote: [ -> ]Coincidentally, this just came up as as issue on the lsynth github.  The net generator spreadsheet could be used to model that.  But you'd have to do it in 2 parts, and you might want to substitute string parts for the box primatives.  There's a link to the net generator download somewhere in the issue messages.  https://github.com/deeice/lsynth/issues/5

I knew I had seen this before:
http://www.sayce-jones.co.uk/lego/cad/net/index.htm

The idea for cloths is interesting too.

Basically the net is a bit the same.
You'd have the flat net and when you pull one of the knots, the shape should be formed.


However, I can certainly imagine this is very difficult to program.

Thanks for your efforts.

(2020-04-15, 9:15)Jaco van der Molen Wrote: [ -> ]The idea for cloths is interesting too.

Basically the net is a bit the same.
You'd have the flat net and when you pull one of the knots, the shape should be formed.


However, I can certainly imagine this is very difficult to program.

Thanks for your efforts.

Google told me there are a couple of open source cloth simulators out there, usable with Blender for example. But again, the details of this stuff are a mystery to me, so I have no idea whether any of it would be helpful for LDraw.