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View Full Version : Problem Modeling Belt Holes

03-23-2007, 01:53 PM
To me ahole in a mesh is not a plane with a hole in it... It's a cylinder with extruded edges ;)
- Take a look at this first picture. Here I have a plane with divisions 1 and 1. The nurbs Circle indicate where I want a hole:

http://www.final3.com/images/resources/tutorials/cgTalk/wii/cuttingHole_00.jpg

- Then I replace the circle with a cylinder with 8 spans. I usually do this right away. The circle was just for showing you where I wanted the hole. I snap the pivot to the top of the cylinder and then snap it to allign with the plane. Now I have a dummy I can snap vertices to. (note: You don't have to do this. You can also snap in one of the axis at the time and therefore not bother how high the cylinder is. When the object is flat of course...)

http://www.final3.com/images/resources/tutorials/cgTalk/wii/cuttingHole_01.jpg

- Whenever I can I only work with one half of the object. This way I can focus on modeling only on one side and then mirror it. ( for the object I create in this minitutorial I could have deleted the bottom too leaving me with 1/4 of the mesh and then mirror it in -Z and +X ) I slice the mesh with splitEdgeRing tool at the middle of the mesh and also to match the corners of the cylinder. One usually misses this point by a few pixels. Therefore I select the edges and snap them to the cornerVertices in the X axis only.

http://www.final3.com/images/resources/tutorials/cgTalk/wii/cuttingHole_03.jpg

-Now it's time to cut the remaining shape of the cylinder on the plane. See yellow lines:

http://www.final3.com/images/resources/tutorials/cgTalk/wii/cuttingHole_04.jpg

- After you snap the new cuts so they allign perfectly delete the "hole" you now posess and delete the whole cylinder too. We don't need it anymore.

http://www.final3.com/images/resources/tutorials/cgTalk/wii/cuttingHole_05.jpg

- Too keep the quads you might want additional cuts. Remember to snap any misplaced vertices.

http://www.final3.com/images/resources/tutorials/cgTalk/wii/cuttingHole_06.jpg

03-23-2007, 01:54 PM
- Grab the edges that define the hole. Now we need to extrude this down and you might also want to scale it a bit inwards. (this totally depends on the shape of the hole) You can go to scalemode and hold d+v to snap the pivot in the X axis here to allign it to the center of the hole. (Alternative: Keep the cylinder and snap it to its center in the x-axis.)

http://www.final3.com/images/resources/tutorials/cgTalk/wii/cuttingHole_07.jpg

- If you try to smooth this you'll notice that you get undesired result on the flat part. Therefore I use split poly to create another outline (yellow). This leaves us with some triangles (red) Save image and scale to see it better. To get a perfect split go into the stack where you can locate the last split and type in the correct values:

http://www.final3.com/images/resources/tutorials/cgTalk/wii/cuttingHole_08.jpg
http://www.final3.com/images/resources/tutorials/cgTalk/wii/cuttingHole_09.jpg

- Select the edges that create these triangles and shift+rightClick(HOLD)-> merge/collapse edges->merge edges to center.

http://www.final3.com/images/resources/tutorials/cgTalk/wii/cuttingHole_10.jpg

- Now smooth it to see the result:

http://www.final3.com/images/resources/tutorials/cgTalk/wii/cuttingHole_11.jpg

When you know that you need several holes you have to plan out how you want to cut things. It's easier to see this if you place these cylinders around. You don't want a too messy wire so therefore the planning BEFORE you start splitting things is very important!

Hope this was clear :)

03-23-2007, 02:59 PM
Another thing. When modeling stuff that has a shape like that (belt, wheel etc.) you can model it flat and then use a bend modifier to get that round shape ;)

MarcusKyler
03-25-2007, 04:01 AM
Thanks alot, you've made my weekend! I hated stressing out over something when I only had a little bit left to go. This is an excellent tutorial, I wasn't expecting anything this in depth. I will be sure to try it, glad to see a good method that works. Thanks again and I'll post my work once it's finished, almost done now.

03-25-2007, 07:55 PM
No problem. Hope you can get it to work !

kirigoi
03-26-2007, 03:21 AM
Hi MarkusKyler,

There's always problems putting small local detail into large curved surface as you have to maintain the smoothness of the belt (which requires well spaced edges), with having adequate detail in the belt holes (which requires edges to be close together). Although Mikademius's method is how you should go about making the holes, there's one other subtlety worth mentioning:

In your belt model as shown there are areas where edgeloops are clustered together, making visible creases around the belt, like this (they are particularly visible in the smooth shaded screenshots):

http://www.skylight3d.com/images/CGTalk/screens/belt_01.png http://www.skylight3d.com/images/CGTalk/screens/belt_02.png

You can see the bunched edge loops that are causing the problem (circled in red):

http://www.skylight3d.com/images/CGTalk/screens/belt_05.png

Strictly speaking the edge loops running between the belt holes aren't causing a problem with curvature (as they are running along the curve rather than perpendicular to it), but they result in a heavy model as you are using more polygons than needed.

You should be aiming more for a result like this:

http://www.skylight3d.com/images/CGTalk/screens/belt_03.png http://www.skylight3d.com/images/CGTalk/screens/belt_04.png

as the edges making up the belt are much more evenly spaced, giving a nice curved shape. In addition, it uses less polygons to make the shape (590 compared with 720 for the first one). Finally, all the polygons that make the hole are quads with no vertices attached to more than 4 others, which can help stop pinching of the mesh.

There's a modelling trick I use to get from the first model to the second, and often find it useful.

First split the middle edgeloop into two (circled in red), which will stop you from getting a high-valence point in the middle which will often result in smoothing glitches. Then add extra loops horizontally (in green):

http://www.skylight3d.com/images/CGTalk/screens/belt_06.png

Now weld the green points to the middle ones as shown in the arrows in the diagram below, then delete the remaining edges (struck through in red). You will need to do this for each belt hole, but it's only a few operations and doesn't take long. You will also need to tidy up and delete any 2-vertex polylines that result from these operations (this can be done at the end).

http://www.skylight3d.com/images/CGTalk/screens/belt_07.png

When you do this for all the belt holes you should have the following, which doesn't have the problem with the creases.

http://www.skylight3d.com/images/CGTalk/screens/belt_08.png

Finally, when you want to add a buckle, just rotate the polys that make up the belt hole (leaving the outer ring unrotated), then with minor tweaking of the outer points you should get a nicely deformed belt like this:

http://www.skylight3d.com/images/CGTalk/screens/belt_09.png

Hope that helps. Let me know if you don't understand any of the steps or the reasons for doing them. M

03-26-2007, 06:06 PM
Nice teamplay kringoi :)

kirigoi
03-26-2007, 06:48 PM

Hopefully between the two of us we've got belt modelling covered ;)

M

03-26-2007, 07:18 PM
Hehe, yeah :)
Now where do we go next ;) ?

03-26-2007, 09:11 PM
the big 'ol rodeo belt buckle!

kirigoi
03-26-2007, 10:12 PM
Hehe, I didn't bother doing the rest of the belt to scale as I wanted to focus attention on the holes and buckle, but you're right, that's one huge belt!

funkyfoe
03-28-2007, 10:43 PM
hehe This is what i would do :)

what can i say....I`m a cheap bastard when it comes to polys ;)

MarcusKyler
03-29-2007, 12:21 AM
Beautiful!!! Thanks kirigoi and funkyfoe for adding to this, these are some good low poly techniques. Well I'm done with the other parts, I'm going back to the belt tonight. I'll see how it goes now that I have more options.

MarcusKyler
04-03-2007, 05:14 AM
This techique worked well, my problem has been solved. Thanks for your help guys.

http://i47.photobucket.com/albums/f152/Masta_Marcus/Belt/belt9.jpg

http://i47.photobucket.com/albums/f152/Masta_Marcus/Belt/belt10.jpg

http://i47.photobucket.com/albums/f152/Masta_Marcus/Belt/belt11.jpg