Some questions I always wanted to ask

Laszlo KREKACS laszlo.krekacs.list at
Mon Apr 20 14:33:25 CEST 2009


Steve, you pretty much explained everything what I wanted to know.

And for the case, I accept the decision, and it makes sense this way.
I completely missed the tooling charge from my view.

Lets say a new case costs 400.000 dollar, I assume, we can
change the case after 40.000 unit sold (would be 10$/unit the case).

So it is extremely important to make the case design as open as possible,
to come up with a nice case, which can stand for multiple years.
(and not a bottleneck of selling)


I see basically 3 levels of community involvement in the new case design.

1st level:

The first level would be concept sketching, where basically the community
would propose the ideas, and explain it with drawings.
These drawings can be scanned drawings, illustrations, etc.

This level basically does not require any specific software.

2nd level:
The second level would be the community models the actual device
which fulfill some engineering requirements.
So the model would use some real units, have sufficient inner space,
took into account the RF issues, so have space for the antenna at some
specific locations, etc.

BUT it is not fabrication ready. It cant be send to moulding as is.
There need to be a mechanical engineer, who proofread the design and
REMODEL it in an appropriate 3D cad tool.

This task only requires some 3D modelling tool. So mesh editing is enough.
No need to have a 3D CAD software.

3rd level:

The community would do everything, from concept to final 3D CAD modelling.
No need to remodel the design in a CAD software, because the community
would do it.

The only problem with this approach, there are no free software to do this.
Either the software is not finished, or not up to the job.

In this case OM should invest (with programmer or money) to help implement
 or finish a specific free software.

BUT this step is really at the end of the process. At that step the case
are modelled, the look is pretty much finished, and
this step is only needed to be able to *fabricate* the actual case.

>> - 3d CAD program. The closest free software:
>>   Wildcat-cad:
>>   HeeksCAD:
>>   BRL-CAD:

>Hmm, Wildcat is Open Source but the Linux port hasn't been completed
>yet. There are also:

>- Wings 3D:
>- Art of Illusion:
>- FreeCAD:
>- Blender:

>Can HeeksCAD import the GTA01/02 files ? It looks promising but
>doesn't even start on my system :-( FreeCAD can handle the STEP
>version. BRL-CAD fails in various ways to convert the IGES. The
>others can't handle the file formats Openmoko has released.

>Art of Illusion is actually surprisingly nice. It looks weak when
>it comes to CAM integration, but given that the RepRap folks have
>chosen it as their favourite, there ought to be a way to do this.

Ok, lets distinct the 3D programs into two categories:
- Mesh modeller program
- 3D CAD program

In the mesh modelling category every model are meshes, ie. triangles
in the space.
So there are no true circles or cylinder or any curves which cant be
made using triangles.

In this category falls:
- Wings 3D
- Blender
- Art of illusion
- Google Sketchup

If you modelled something using these programs, you must redo them in
a proper 3D CAD
program to be able to fabricate it.

In 3D CAD category falls the following programs:
- Wildcat-cad
- HeeksCAD (not sure, didnt try out)

Commercial programs:
- Autodesk inventor
- Solid edge
- Catia
- Pro Engineer
etc, etc.

When you models something, they are made from mathematically correct objects.
The cylinders are true cylinders, circles are circles and not polygons.

In that category none of the free softwares are finished and hardly usable.

The most promising app was Wildcat-cad, but it is basically a one-man
project, and
the original author didnt touch it since december.

And it lacks some essential features like boolean editing. I was able
to try it under
windows (I tried out at work, because there were windows installed),
and looked promising
mostly the 2D editing part.

I assume the program needs 6-9 man month to be usable. Either pay to
the original author, or
hire a programmer.

BRL-CAD simply lacks the gui. It is nightmare to do any real and
appealing work in it.
It is like using inkscape versus editing the .svg file with vim;)

Reprap project choosed Art of illusion because it is relativily easy
to start modelling with it.
But it lacks some very vital function and because of this it is
cumbersome to model in it.
(like boolean add. It results often a corrupt model). Oh and just some
of them use
art of illusion, autodesk inventor and proE was used too. And more recently one
member found CoCreate, which are free for personal use (windows only).

And it is a polygon modeller program (AoI), like blender, just more
easy to start with.

And for the reprap objects it is perfectly good (and enough) the mesh
objects. It "rasterizes" the 3D object
anyway (when printed).

These are just toughts, Im not an expert, so if there are mistakes,
please correct me.

Best regards,

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