Why does a part of the legs' armor plates bend when I smooth them?

[alo95.costa]

The basic model is very simple, as you can see in the Pre-Smoothness stage. But when I switch to the Post-Smoothness level, the top part tend to bend backward.

Like I said, the basic model is very simple and clean, so I really don't get what seems to be causing this bending.

[mspeer]

Hi!

That's simply how OpenSubdiv works.

1. You are using triangles that's not a good idea.

2. The mesh is not closed.

OpenSubdiv uses some sort of interpolation between neighboring faces/edges, without neighbor faces this may lead to unexpected results.

As written in previous posts, Smooth Mesh Preview is not a one-button-make-all-look-good solution, the mesh has to be prepared to work with this, if not please use some other methods to add more faces/edges and smooth your mesh.

[alo95.costa]

Hi mspeer, thanks for your advices. However:

1. I admit I also noticed the presence of the triangles. However, even though I had removed them, not much had changed. Sure, the part highlighted in the screenshot in my first post did not bend anymore, but now I was getting a result more like that shown in the Post_Smoothness_No_Triangles screenshot below.

2. Could you explain what you mean when saying that the mesh "is not closed", please?

3. Also, I have also tried other solutions to add more faces/edges (I even tried edge loops), but after smoothing the mesh, the result was more or less the same.

[mspeer]

Hi!

1. Let me correct 1. to "Use quads only".

The new result looks much better.

2. If you would delete some faces of a closed object like a cube or a sphere it would become "not-closed".

I see now in your new screenshots that your model has thickness, so it's already a closed volume.

3. Build the model as you want it to be without Smooth Mesh Preview

or

build the model to show up as you want with Smooth Mesh Preview applied,

you can't have both.

You need to model with Smooth Mesh Preview already applied/enabled to make it work with this, it's NOT a simple post process that keeps your model, it changes it, that's how it works.

[alo95.costa]

Hi, apologies for my late reply.

1. Thanks for pointing that out, but I already figured out you were referring to the use of quads instead of triangles. But even after having cleaned the model, the problem keeps showing up. Sometimes it looks like it bends even slightly more than before, though.

2. Oh, I see. Yeah, it does have thickness.

3. Yes, that's how I always work. I build the basic model without the Smooth Mesh Preview applied, and then I continue with the SMP on.

[mspeer · Accepted solution]

Hi!

The "bending" is just part of the algorithm, there is no other way than to edit your model, with the changes applied by the smoothing in mind/viewing.

[alo95.costa]

I see. All right, I'll see what I can do to fix that bending problem in order to get a properly smooth prop, just like the rest of the 3D model. Thanks for your tips and advices!