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The fraught question of 3D modeling for ReprapSunday, July 06. 2008
The
Reprap effort has made a remarkable effort not only to pursue the
development of an open source 3D prototype machine but also to use,
wherever possible, open source development tools in its development.
While that ideal has largely been carried out in reality, the selection
and use of the open source Art of Illusion 3D modeling tool has been, perhaps, one of the more heavily contested choices in this regard... read more
Almost from the beginning of the Reprap project, the choice of Art of Illusion (AoI) as the 3D modeling tool for Reprap has been more honored in the breach than the observance. Indeed, when the Darwin prototype emerged the parts were modeled, if memory serves, with Siemens' SolidEdge and had to be converted with considerable difficulty into AoI formats. Indeed, even now a rather heated discussion of alternatives to AoI is taking place in a forum thread to which I've found myself making a number of ill-tempered additions. Let me say that I began writing coding that did perspective drawing, rendering and the beginnings of CAD way back in 1968. I've used any number of CAD packages and written a few of my own from time to time for special purposes. Possibly because of this, I didn't find using AoI a particularly difficult challenge. It seemed largely intuitive as a 3D modeling tool. Mind, it had a variety of shortcomings the most notable of which was a tendency towards memory leaks, a well-known problem with the Java programming language in which AoI is written, that had a tendency to completely take over all your PC's available DRAM. Still, in spite of these faults, I've found myself amazed at the animus that AoI has drawn from any number of Reprappers whose association with the project has ranged from casual to heavily committed. From the onset of Reprap Dr. Bowyer set a secondary specification of the STL file format as being commonly acceptable by the slicing and dicing routine that he wrote so that virtually any commercial or open source 3DCad package could be used. The problem with STL, however, is that it consists of a simple traingular mesh fitted to the surfaces of the part and contains no information about the primitives or operations that went into the part when it was originally designed. Because of all of this there has been a steady refrain on the theme of "AoI sucks because..." which usually winds up with a wistful moan to the tune of "why can't we have a 3D Cad package more like ... {whichever commercial 3D modeling package the complainant is currently using}". Solutions to the problem have ranged from the usual suggestion that we use some other open source modeling package, either fully or partially developed, or some free but cut down version of an existing commercial app. All along the way for the past two years AoI has been mentioned practically in the same breath as the Blender app. I first looked at the Blender app some two years ago. At the time it struck me as a user-hostile piece of software that completely violated what I took to be be an implicit rule of Reprap, viz, that it should invite people to participate rather than scare people off. After following the AoI alternatives thread in the forums for a few days and having mentioned Blender as an alternative myself, I decided that possibly I ought to give it a second look. My first reaction on getting into the website and tutorials for Blender was one of shock that such an app should have come so far in so short a time. Actually, "so short a time" is a misreading of the situation in that Blender began as an animation package back in 1989 and wound up as orphan code when its Dutch firm went kerfloppo during the dot com bust in 1992. It was ultimately bought out of the bankrupcy suit and became the core code for the Blender foundation which is alive and prospering since it really got rolling in 2006. A look at the Alexa ratings for Blender, AoI and Reprap gives you an idea of the size of it's user community.  At the onset let me say that my general impression of Blender is that it is a rather powerful open source animation app, not a 3D engineering Cad app per se. Recently, the Blender Foundation made a short called "Big Buck Bunny" which gives you an idea of just how powerful it is. You can see the full short here. I started working my way through the tutorials yesterday and made some good progress over the evening. My general impression was that I had wandered into a complicated technical discussion that had been going on for quite some time for which I knew little, if any, of the jargon and even the concepts. The GUI was as intimidating as the Space Shuttle's. After several hours with the tutorials and the PDF's, however, things began to make a limited sort of sense. The tutorials were of marginal usage since they were aimed at people wanting to create objects for animation and not for people wanting to make close-tolerance parts for something. One thing that was very easy to do with Blender, however, was to make fillets and round edges. The ability was intrinsic to the app and didn't need anything resembling an add-on script. As well, user scripts are written in Python, a much more compact language than Java, something that ought to please Enrique no end. Blender has a quite extensive user manual in two parts. It includes the usual Pythagorean primitives such as cubes, spheres and the like. Given the drama that Nophead (Chris) had been having with AoI's Boolean ops module I gave that part of Blender a hard look. I laughed when, at the bottom of that section of the user manual I found the little note... Sometimes the boolean operation can fail with a message saying ("An internal error occurred -- sorry"). If this occurs, try to move or rotate the objects just a very small amount. ...which is exactly what you have to do in AoI. My general impression of Blender is that it might serve as a useful alternative to AoI. I doubt that existing users of commercial CAD/CAM apps are going to be taken by storm by it, however, given that its emphasis is on animation, not engineering design. That said, I suspect that with a few focussed tutorials it could serve well as avery useful alternative to AoI for advanced Reprappers. I personally think that AoI ought to remain as the entry-level 3D modeling package for Reprap. It has a non-existant learning curve and even young kids can become useful with it in a minimal amount of time. The busyness of Blender's GUI is going to intimidate new users of any age. After a while, though... Trackbacks
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I've been playing with Blender for a while for the purpose of 3d animation. It's a great program, built from the ground up to make the art of creating computer animation as efficient and powerful as possible. This means skillfully placed shortcut keys, not immediately intuitive layouts. I found the main documentation to be quite helpful in giving an overview of the underlying structure of the program. Such a top-down view helps make sense of the otherwise alien interface. The user-supplied tutorials were of less help to me, since they tended to be example based rather than concept-focused. While it's a fantastic and powerful program for the artists who are willing to spend the time learning it (it's actually kindof pleasant if you go through the official documentation), it is certainly not like other programs and therefore not as intuitive as what the RepRap project needs.
Why not use BRL-CAD for reprap? It is open-source and uses constructive solid geometry (CSG) instead of polygons or boundary representation. This seems like a better way to model physical objects you plan to construct, rather than just render as images.
BRL-CAD seems a lot less intuitive than blender. I downloaded it to see if it would be better than Blender, and couldn't figure out how to get the first shape out there. Lots of acronyms in the menu system, etc. Probably with tutorials etc, it would be okay, and if it address engineering issues beyond what blender provides, then great.
However, I have not had any problems with blender myself. It took me a day or two to be able to create crude models about 2 years ago. It is now very easy, and AoI is the 3d modeler that seems to have a non-intuitive interface. It all comes down to what you have used before.
Standardizing BRL-CAD for RepRap would be like standardizing on using vim as a replacement for an office suite. If you know what you are doing, it'll do everything you'd want (although there are some other limitations for BRL-CAD that make that a subideal analogy), and it'll give you a whole lot more power quickly if you sink a good chunk of time into learning it, but it'll send most people who are used to long, shallow learning curves running.
As far as IFC is concerned, it looks pretty good as an interchange format; there's a huge mount more there that is irrelevant to a reprap, but that can just be ignored. the problem then is finding a program that would support it. I would also wonder if it actually provides any mechanism for the programming-style editing that engineers seem to be used to - someone using a pattern tool tends to want to be writing a small program that generates the pattern of features they want - so they can change the feature, or the program, without having to run the steps again. What I would like is really a general system for writing that kind of macro (in the lisp sense of a function that translates what i write from a higher-level to a more basic form). But that's just me.
Except, unlike with vim, brl-cad has identified a user friendly GUI as a high priority development project.
So the limitation inherent in STL files can only be overcome by using a native file of some 3D program or another?
What about an alternative file type? For instance, I'm curious to know if IFC would be suitable or not: http://en.wikipedia.org/wiki/Industry_Foundation_Classes
Ive used blender and was eventually able to get adequate with it, however almost none of the export file types actually worked so I abandoned it. I have been using Wings3d, and have become extremely good with it. It even exports to STL and the latest version can make gears for you, just specify the size and number of teeth. The only thing I have not found in it is the ability to configure the unit size to millimeters so I will probably export and use AOI for that.
Which version of Blender did you use? I'm using version 2.46 and it appears that you can export objects in STL format.
I'm very interested in your experience with Wings3D. I gave it a quick look a few years ago, but haven't checked back on it recently. Have you blogged or otherwise published about Wings3D? If not could I talk you into doing so?
Im not sure which Blender version it was but it was around december 2007 - Jan 2008 so not too long ago. Otherwise I have not really wrote much about wings 3d except I have posted a pic of one of my creations on a fourm.
http://www.dzxproductions.proboards46.com/index.cgi?board=art&action=display&thread=667
It has an optional orthogonal view (like a cad program) and of course snap to grid and such that helps with percision. Otherwise if you want a smoth high poly version of a simple model it smothes it for you. You can also view the smoth version wile you work on the low poly version.
Wings 3d is at version .99 as of this posting and has added plenty of new things just since version .98
I may post more pics but none of the other models have been colored or skinned.
Wings3d website:
www.wings3d.com
Hello.
Here are a couple tutorials from a guy using Blender 3D for precision modeling:
http://www.rab3d.com/tutorial.html
It's worth a look.
It appears that Google Sketchup 6 and the LTplus.rb scripts can produce a simple, passable dxf or stl.
I know SU is not open source and only a facet modeller, but it seems to have a strong user group, a reasonable API and a shallow learning curve. (Have I used it, yes. I'm not about to model turbine blades with it). It seems to me that if one wants class A surfaces, it's probably best modeling the surface in Scilab and exporting at a resolution suited to the output machine.
http://www.ltplus.de/
i am glad to see i can use google's sketchup with it, i am familiar with that one, and am most comfortable with it
though i was kinda hoping to see it would work with a little less trouble.
if you want to use blender for architectural works, look for a script:
procad
you can find it @
blender.it
there was an elgnish version, too, but i don't remember where
wings 3d is easy
blender in very good after some time you use it
sorry for my poooooooor english
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