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 From:  Oskar_L
3183.1 
Hello everyone!

I've just bought moi3d I am no expert in nurbs modeling. I'm courious how you go about to model something like this. I'm having an hard time to get a smooth transition from the top cube to the more elliptic tube. I've tried to get it to work with the blend tool. But i cant figure out how the get the same amount of edges on both sides.




Hope you can understand my ugly sketches.

Grateful for any help!

/Oskar
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 From:  Michael Gibson
3183.2 In reply to 3183.1 
Hi Oskar, could you post a 3DM model file with your current attempt at doing it with Blend?

Seeing that would also probably help to understand your sketch better - you mention a smooth transition between the cube and the main body, but in your sketch it looks like there are mostly sharp transitions there? Is it only at the top that it should be smooth?

It may be possible that you would want to model an initially larger more simple smooth piece, something like this:



Then use booleans to cut it and remove pieces you don't want, like this:








That kind of workflow of "build it simple and larger/extended initially and then cut back" is frequently used in NURBS modeling but it is rarely used in polygon modeling so that can take a while to get used to this different technique if you come from a polygon modeling background.

If you are using Blend from the beginning it probably means you are trying to build things in a kind of "patch by patch" method instead of utilizing larger simple pieces and cutting... That can be ok for certain kinds of things but it is more general that you would want to try to do more of the "cut things out from a larger smooth form" type thing.

In NURBS booleans should be more of the first way you try to build things, rather than something that you would avoid like in a polygon modeler.

If you can post some model files of your current attempts it would help to understand what you are trying to do a lot better though.

- Michael

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 From:  Oskar_L
3183.3 In reply to 3183.2 
Hi Michael!

Thank you very much for your response!

It is always inspiring to see your tips and trix!

I made a sketch in Maya to show what I am going for. I didnt save the .3dm with the blend attempt. It wasnt close enough anyway.



The problem is that I cant figure how to get a clean mech. I have tried to make the tube from both loft and sweep. Sweep takes me closest to the shape I want. But then the I get problems when I union the tube and the cube and try to fillet. Since I need the bottom of the tube to be square I get this edges going along the tube. These edges really narrows my fillet.

How would a pro solve this?

The example you showed looks intreseting. But how do you go about to get the tubes "shoulders" rounded? Booleans?

/Oskar
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 From:  Michael Gibson
3183.4 In reply to 3183.3 
Hi Oskar, tomorrow I'll try to give you some more tips.

But it looks like your cube part is more of a separate distinct module and not really behaving so much as if it was just a continuation of the other base part. So the way I wrote previously is probably not what you would do for your case here.

The more difficulty you have in describing your shape by 2D plan curves, can also tend to mean that you may be better off doing it in Sub-d rather than NURBS actually - NURBS are the strongest when you can leverage 2D profile curve patterns to the design and utilize those 2D curves directly.

The more melty looking and less defined by plan views your shape is, then the more advanced and difficult kinds of NURBS modeling techniques you tend to have to use. You are probably getting more into that area in this case.

So you're kind of jumping into the deep end right off the bat here...

Are the shoulder parts supposed to be actual spheres?

I'll take a closer look tomorrow but it looks like I would build some pieces of spheres or revolves for the shoulder part, with an extrusion connecting between them, then either Loft or Sweep for the main body and probably leave some space between the end of the main body and the shoulder and put in blends to fill that in. Something like that anyway. The problem with working on a patch-by-patch basis like that is it tends to be difficult to get the patches to be perfectly smooth to one another - MoI does not actually have a full set of tools for ensuring that yet (like it does not have a Match tool yet for altering an existing surface to become smooth to its neighbor, you have to try to use fillet or blend instead), so I'm not really sure if it would really be the right tool for the job really.

- Michael
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 From:  Michael Gibson
3183.5 In reply to 3183.3 
Hi Oskar, here's an attempt:





To start with I went to the Front view and drew in 3 rectangles with the "Rounded" option enabled, and I made the round take up as much space as possible to make them into lozenge type shapes:



Then I went to the 3D view and dragged them apart to separate them (make sure Straight Snap is on):



Then a Loft to build a surface:



At this point you would do quite a bit of fiddling with editing the curves to scale them or move them forward or back a bit until you would be satisified with the loft shape.

So that builds the main body part.. I then hid those curves. Your shoulder part seems to be quite sphere-like so I decided to actually use a piece of a sphere there. To do that I selected these edges:



Then Construct > Revolve, set Angle: 90 degrees option before picking the axis points:



Mirror that sphere piece to the other side, then select these edges:



And then Construct / Extrude to build the center part:



So now you've got the basic piece but the issue is that there is a kind of crease where the sphere and loft touch each other. Normally when you have a sharp crease you use Fillet to round it, but Fillet will tend to have difficulty and fail in places where the crease is at a shallow angle where it is actually not that far off from being tangent (like say 20 degrees or less). Also the fillet in such things will be a very small area and may not give you the kind of broader transition that you would want.

What you would really probably want at this point is a surface matching tool that would reshape the loft so that it was smooth to the end part, but MoI does not have that tool yet.

So anyway, I figured I would put some blends in here. So as a first step I decided to start the shape going straight off the sphere pieces rather than trying to do a blend directly to the spheres, which because the spheres are curved fairly tightly it is going to have more of an effect on the blend making it kind of more wavy than you would want. So I moved the end pieces over some:



And extruded the edges there to get a really straight section going:



So now to blend this - often times you want to let blend have some area to work in, if you give it a small zone that will generally tend to make the blend rather tightly curved itself which will be more apparent in the shape of the result. It can be small if the pieces are really very close to being aligned to one another though.

So I drew in a line a ways back here:



And used it to cut that piece off, so in this will be the zone that Blend will fill in. Also at this point I decided to delete the bottom half and mirror it later.

Some of these decisions came after experimenting with a few different varieties of how much space to put in there. This is where things kind of get fiddly and more difficult to judge what to do without experience. When you use NURBS modeling to build things that are driven off of 2d plan views, it doesn't take anywhere near as much experience because it is just more obvious to use the 2d curves directly...



So then some Blends between these pieces, adjusting the Bulge down slightly:



Then the top is pretty darn flat, so I just selected the 4 curves and used Construct / Network to fill in a surface to that 4-sided boundary.



Then mirror that whole thing to get the bottom part.


For the cube I drew in a box, filleted the vertical edges, went to the side view and rotated it, then draw a line along one of those edges, moved the line to the side and used perp/perp snap to find the spot on the arc that was closest to that angled line for where to place the box (see http://moi3d.com/forum/index.php?webtag=MOI&msg=3042.14 for a demo of perp/perp), then boolean union, then Fillet the bottom.


Anyway, it's kind of getting into the more arcane and fiddly aspects of NURBS modeling, that's why it's a more difficult area to jump into.


When your shapes don't have very distinct edges to them and are rounded and semi-melted looking all over the place, those are usually indications that you could get a better result with sub-d modeling tools for that rather than profile-driven drawing tools like MoI has put as more of a priority so far within it.

- Michael

EDITED: 23 Dec 2009 by MICHAEL GIBSON


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 From:  Oskar_L
3183.6 In reply to 3183.5 
Hurrah! Bravo! Splendid!

Thanks!

Unfortunatly there is no sub-D modellerer with such a devoted developer. So I guess I do all my work in Moi from now on. Maybe you should consider offering some lectures about customer support to autodesk.

But seriously, I would never consider character modelling in Moi, when it comes to product design subD's doesn't really seem to be an option. Even with a modeller like Modo you are far from nurbs precision.

Anyway I made a test scene and got it to work. My geometry wasn't as clean as yours. This was caused by the square profile at the bottom of my tube. But with an extra vertical trim I was able to make it work. And I really liked that perp/perp snap.

Finally I have a question about booleans. Sometimes I have to use the union command twice to really union two object. First attempt only cuts them. What is causing this? When I united the tube and the cube this happened. I attach my test file.

Thank you and God Jul! (Merry christmas in swedish)

/Oskar
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 From:  Michael Gibson
3183.7 In reply to 3183.6 
Hi Oskar, Merry Christmas!

Re: Sub-d - T-splines (http://www.tsplines.com/) could be worth checking out as a tool for squishy/melty/blobby type stuff, it basically gives you a sub-d type workflow but can generate NURBS surface data out the other end.


> Even with a modeller like Modo you are far from nurbs precision.

Yes, that's true, for example some pretty simple things like a 100% exact sphere doesn't really work in sub-d, the basic sphere shapes are just pretty close to being like a sphere but are actually slightly ovoid-ish. And in sub-d it is horribly difficult to cut a hole in something where the hole has an exact shape like a circle of a specific radius value.


But on the other hand, with an example like your specific model here, you are pretty well leaving the world of precision in a lot of ways already... For example your model was not defined by a set of plans with specific dimensions on them, you didn't have things like fillets that had to be one specific radius in one part of the model, stuff like that.


Not every kind of product design has a focus on precision and conforming to particular specs or stuff like that - if the focus of the design itself is more on overall blobby smoothness as a high priority then a lack of precision does not particularly harm you for that particular design...


I'll take a look at your boolean problem.


- Michael
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 From:  Michael Gibson
3183.8 In reply to 3183.6 
Hi Oskar, so your boolean thing is because one of your pieces there was an open surface and not a solid.

The booleans are more oriented towards using solids, the different kinds of booleans (like difference vs union) are about different ways of combining the "insides" or "outsides" of the shapes and if you do not have a solid volume there is not a well defined inside or outside volume to it.

So it can be good to solidify objects before doing booleans on them, so that they work in the most expected way.

To do that for your case, select the tall body piece and then run Construct > Planar - that will cap off the open square bottom by putting a plane in there, and then it will be a solid. After you have done that, then you should see that doing a boolean union gives you the proper result right away.

In MoI v2 there is an object type readout in the upper-right corner of the screen that will tell you if the selected object is a solid or not:



If it does not say Solid there (either Joined Srf for more than 1 surface joined together but not closed, or just "Surface" for an individual surface that is not closed) then it means that there is still a gap or hole in the object somewhere.


The booleans will still try to cut things up when not working on solids, but usually you will want to use Trim on non-solids instead. Trim does not try to discard things based on volume but rather it lets you pick the pieces you want to get rid of.

- Michael

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 From:  Oskar_L
3183.9 In reply to 3183.7 
T-splines could be worth checking out in the future.

You are right about this model. But it is alot easier to create plans and drawings from a design created in moi compared to some smoothed poly mesh from maya. In moi I know the radius of my fillets. :)

By the way, i noticed that it is really convenient to import illustrator files. Is there any way to export curves back to .ai or .dwg?

/Oskar
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 From:  Michael Gibson
3183.10 In reply to 3183.9 
Hi Oskar, yes generating 2D illustrations from 3D does tend to work better with NURBS models.

NURBS models in general are made out of broader surfaces which then in turn helps to get longer smooth curves to go in the drawing rather than a bazillion little jaggy lines.

MoI does not have a whole lot of stuff in this area yet, but there is some support currently.


> Is there any way to export curves back to .ai or .dwg?

Yup, AI is supported for writing curves. If you just do a SaveAs it's in the file types list there (scroll it down) and it will write out curves and edges to a 2D AI file.

If you have solid objects and you want to get a drawing from them, you'll probably want to use the Construct > Curve > Silhouette command to generate its silhouette curves first before exporting.

For some examples see:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3000.30
http://moi3d.com/forum/index.php?webtag=MOI&msg=3000.32
http://moi3d.com/forum/index.php?webtag=MOI&msg=3000.33

- Michael
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