Full release of the mechanical design

The potential for branches in the mechanical lineage of RepRap is one of the prospects that really excites me about this project. If even 1% of the potential userbase spends a bit of time modding their machines, we should very quickly develop a vast database of mechanical tweaks, some (of course) more successful than others. Given time, these successful tweaks will become apparent and be adopted in the general community, propagating themselves into the next generation of the RepRap design.

I'm hoping to make some experimental modifications to the design myself. Unfortunately, at the moment I'm limited by the fact that the dev team has not released the computer aided design (CAD) files for the machine in an open engineering format such as STEP or IGES. The only formats that the latest versions of the design are available in are STL and Art of Illusion files, neither of which are useful for this purpose.

STL is an inherently limited format. It only describes a surface, not a solid object, and that surface is constructed of triangles, not curves (although curves can of course be very closely approximated with large triangle counts). These particularities make it a great format for use by the host software in printing - the data are relatively simple and easy to parse (not to underestimate the work Dr. Bowyer put into the slicing code!), compared to other formats. However, because of its nature a .STL file is very difficult to modify, once it has been created. It can also be a challenge to extract useful dimensions from it, such as the distance between two hole centers. These properties make it more of a "compiled" format than "source code," to make a software analogy.

AoI files are more like "source code" in that they can be easily modified. This is a critical improvement. Art of Illusion is a usable program and has proven its ability to design functional parts many times over. However, it is not widely used in the engineering community, and was never intended to be. AoI is a 3D animation program without many built-in tools for accurate dimensions or constraints, and this limits its applicability in this situation. While it is possible to design the entire RepRap in Art of Illusion, that is in a way analogous to writing the entire host software in Lisp. Lisp is a great language that is powerful enough to do whatever you want with it. However, in my experience there are many programmers who aren't very familiar with it. They would be unlikely to commit the time and effort it takes to learn such a different language solely in order to contribute to this project. In the same vein, some engineers or designers who are already familiar with their flavor of CAD program may be unwilling to learn a new and unfamiliar program (AoI) solely in order to contribute to the RepRap design, even if they have a good idea for an improvement.

Of course, the host software wasn't written in Lisp, it was written in Java, a mainstream programming language. This allows software developers to join the project and (relatively) quickly learn the ropes of the host software, then begin contributing patches. Releasing the CAD files in a program-neutral format would have a similar effect. STEP and IGES are both open ISO standards and are supported in every mainstream CAD application that I have been exposed to.

My request is that the developers release a complete model of Darwin into the Subversion repository in either the STEP or IGES format. My understanding is that the design work up to this point has been completed in Solid Edge (which I know has export capability to at least IGES), and it ought to be trivial to export a copy of the current design in one of those formats. If development is slated to continue forward in Art of Illusion, as opposed to Solid Edge, I will volunteer to be the maintainer of this model, and will manually recreate in it whatever further updates the developers release. I think that this will be a valuable resource for others like myself who would like to digitally prototype tweaks to this design.

Sincerely,
Kyle Corbitt

PS I'd love to get feedback on this request either way. Am I asking too much? Are there others out there who would appreciate this as well?

I tried opening the .stl files in Solidworks 2007, then saving them to .igs and .step files. It didn't like it one bit, complaining there was no solid object. I could save it as a Solidworks .part file but converting that .part file to .igs threw the same error.

Update: Downloading the trial of the Solidworks add-in Import .stl allowed me to import the geometry and not just the graphics. I was able to save to both .igs and .step. The .igs is 6MB and the .step is 3MB, so I can't post for your inspection. However, if you have Solidworks, you can download the add-in. You have 10 days of unrestricted conversion capability, which should give more than enough time to convert all the files.

P.S. If you would like help doing this, I don't really have time until school's over, though I could maybe do a handful if you have specific requests.

Edited 3 time(s). Last edit at 04/13/2008 06:45PM by Ithacacian.

Just to verify, what .stl exactly did you import? I have an old copy of the CAD files for Darwin (far from up-to-date, but most of the major components are the same) that a friend who has Solid Edge exported to IGES for me. The entire assembly is 21MB, and for comparison, when I re-export a single corner bracket as an IGES file, the file size is 1.3MB.

I suspect that what the plug-in (and subsequent re-export) is doing is just saving all of the files as polygon-based solids, which essentially contains exactly the same model information as the STLs that they were generated from. This is unfortunately not much more useful than the STLs themselves, because you still can't get any feature recognition out of it.

However, I would definitely love to look at the IGES and STEP files that you generated to see how exactly they're set up. If you could email them as attachments to kylecorbitt(AT)gmail(DOT)com that would be super!

The features do not show up on the feature tree in Solidworks, if that is what you mean. However, selecting a face does not result in one triangle of the face being selected, as I believe it would in .stl. Curves are reduced to a series of rectangles, yes, but if you want to edit the part, you can extrude or cut with new sketches, and use existing faces in the part for reference.