BRL-CAD provides several ways to model 3D geometry including a graphical tool named mged, another named archer, and various ways to create geometry using scripts. We use 3D models for development and to showcase our features. You can learn the basics of 3D modeling in just an hour or two using our tutorial documentation.
If you haven't yet noticed, our project logo looks a lot like a gear or a couple bicycle chain links. We want you to model an actual bicycle chain with 2-to-10 links.
Model accurate bicycle chain links using the below references. Your job is to model it natively using any of BRL-CAD's tools (i.e., don't model it in something else, don't import anything).
The model should have regions defined for each part (each separate piece of metal becomes it's own region) and no overlaps (use rtcheck and/or gqa commands to verify). Create one top-level combination to group everything together.
Submit a text file or comment describing any resources or web links you used in making your chain and describe your model.
References:- http://en.wikipedia.org/wiki/Bicycle_chain
- http://upload.wikimedia.org/wikipedia/commons/b/b0/Rollenketting.gif
- http://pardo.net/bike/pic/fail-004/000.html
- https://www.google.com/search?q=bicycle+chaintbm=isch
- https://www.google.com/search?q=bicycle+linktbm=isch
- https://www.google.com/search?q=bicycle+drawingtbm=isch
- Submit your model as a .g file (BRL-CAD's geometry file format) and a rendered PNG image. You can run "rt -s1024 -o your_rendering.png your_geometry.g your_top_level_object" to create a PNG rendering of your model.
| File name/URL | File size | Date submitted | |
|---|---|---|---|
| chain.zip | 43.3 KB | January 13 2015 13:14 UTC | |
| chain.g | 39.0 KB | January 13 2015 17:10 UTC | |
| chain (2).zip | 34.2 KB | January 14 2015 10:14 UTC | |
| chain2.zip | 12.4 KB | January 14 2015 15:54 UTC | |
| chain (2).zip | 34.2 KB | January 14 2015 18:13 UTC |
I would like to work on this task.
This task has been assigned to Vladimir Kuznetsov. You have 100 hours to complete this task, good luck!
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But there are overlaps between links and linkers (because of the linkers have no hole). You can create the holes by subtracting the linkers from the links.
In addition you should think of the regions as the building parts of the geometry, i.e. connected shapes of same material/color. Your link regions would be in fact three regions and you linkers regions in fact two.
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A "region" in BRL-CAD is supposed to indicate a single part, e.g., a single piece of metal. That means each link and pin will likely be separate regions or you'll have at least one pin and link region that you reuse multiple times.
Presently, you have regions being unioned into regions, which is considered a modeling error (you can't put a metal into a metal). This error is warned if you run "e chain.c" where it notes that you made all of the links regions, but you also made each of the shapes that comprise a link a region too. That is the source of the error and is easily fixed by making all of the s*.r objects either go away (getting replaced by their non-region version), for example s1.r gets replaced with s1 in link.r .. make sense?
Also, it looks like you have the pins in now, but you missed a hold on the last pin..
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For example link.r has the regions linkers.r and linkers3.r inside. You should read Sean's comment again.
Basically you need only two solids: s1 and a cylinder (e.g. s4). Then you could create a link link1.r by taking s1 and subtracting s4 two times, but with different transformations (shifts). This way you get a nice link with two holes which really can be considered as a region (a peace of metal).
The regions for the pins are even easier to create. You should create for each pin an own region by taking s4 and moving it to the right place.
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You have 15 links which means you need 15 regions for them. Then you have 10 pins which require another 10 regions. Together you should come up with 25 regions.
In my previous comment I explained how you can create one link and one pin. But you need to repeat it 14 times (9 times respective) to get the whole chain.
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