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  #1  
Old 09-06-2010, 07:06 AM
cfuruti cfuruti is offline
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Extending parts without 3D tools - Whammy's Warhammer IIC

Part 0 - Introduction

After building three different Shadow Cats, I've been working on another Battlemech, a Warhammer IIC (thanks to the authors: 3D model by Whammy, unfolded and released in PDO format by Shiftdel, with Sturm's "Multicam" skin). The original scale is IIRC 1/40, but I've printed it at 4 pages per sheet; due to margins, the resulting scale is not 1/80 but roughly 1/95; I estimate the finished height will be about 112mm.
Extending parts without 3D tools - Whammy's Warhammer IIC-pv_wh_multicam_fv_1.jpgExtending parts without 3D tools - Whammy's Warhammer IIC-pv_wh_multicam_fv_2.jpg
I want an articulated, poseable model; however, unlike the chicken-legged Shadow Cat, the humanoid Warhammer's parts penetrate each other at the shoulder and knee, therefore some paper engineering is required. I have neither the original 3D model nor Pepakura Designer, but the original shapes are simple enough (just generalized prisms) to modify using only 2D tools with, I hope, acceptable precision. My tools of choice are Inkscape (vector graphics) and GIMP (raster graphics), both on Linux. A shortcoming of this approach is that's difficult reusing the effort for other skins.

At present, most structural parts are done, and I'll take some time to document my progress, with emphasis on nonstandard steps.
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Old 09-06-2010, 10:45 AM
Stev0 Stev0 is offline
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That is the downside of generic off the shelf 3D models. They really were not meant to exist in the real world under real world laws.

The key is to not only get the parts to go together or sit upon each other, but to ensure that the model will not fall over when posed.
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Old 09-06-2010, 10:59 PM
blaar blaar is offline
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Looking forward to your build since I would really like to see how you plan on making the knees jointed.

Do you also have plans for the ankles ?
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Old 09-07-2010, 06:56 AM
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monkeyrum monkeyrum is offline
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Couldn't you just scale the generic joints set that shiftdel released to make them fit with this model?
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Old 09-08-2010, 05:17 AM
cfuruti cfuruti is offline
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Quote:
Originally Posted by blaar View Post
Looking forward to your build since I would really like to see how you plan on making the knees jointed.

Do you also have plans for the ankles ?
Knees and arms require some improvisation. The ankles were easier - but I only have 2D plans.

Quote:
Originally Posted by monkeyrum View Post
Couldn't you just scale the generic joints set that shiftdel released to make them fit with this model?
Wish it were so simple, but the thighs and shins overlap. The same for the arms and shoulders.
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Old 09-08-2010, 05:29 AM
cfuruti cfuruti is offline
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Part 1 - The problem and the plan

In Pepakura Viewer (PV), here's the screenshot of a rear view of the right upper limb. Texture and shape suggest the "real" mech has at least 3 joints there; the hull/shoulder one is trivial, and we'll take care of the arm/gunpod one later; let's work on the short arm, which swings as shown by the green arrow:
Extending parts without 3D tools - Whammy's Warhammer IIC-pv_wh_multicam_uplimb1.jpg
It's trivial cutting the black hole under the shoulder part:
Extending parts without 3D tools - Whammy's Warhammer IIC-pv_wh_multicam_uplimb2.jpg
However, the arm's upper end must be extended and articulated inside the shoulder:
Extending parts without 3D tools - Whammy's Warhammer IIC-pv_wh_multicam_uplimb3.jpg
Assuming the extended end can be straight, let's draft how it could look like. I provisionally chamfered two edges, which could otherwise constrain the rotation angle; we'll see later if that's enough:
Extending parts without 3D tools - Whammy's Warhammer IIC-pv_wh_multicam_uplimb4.jpg
How much longer must the arm be? I set PV to use the longest possible angle of view (which is not even close to orthographic), align as much as possible a rear view, and take another screenshot. Using Inkscape, I draft upon the screenshot an outline (green) of the arm, plus some auxiliary lines (e.g., the thick red circles mark the edges of the hole cut off the shoulder). Ignoring what appears to be a round handle in the texture, I play around looking for an adequate center of rotation: too near the hole, there won't be enough space to securely anchor the rotation axle; too far, the maximum rotation angle will be too narrow to justify the effort) and consequently the arm's extra length. After that, I can draw a definitive outline; we can see a symmetric 3-sided chamfer provides enough clearance, unless I exaggerate the shoulder back's reinforcement.
Extending parts without 3D tools - Whammy's Warhammer IIC-in_wh_multicam_armplan1.jpg
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Old 09-08-2010, 07:51 AM
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tedparkes tedparkes is offline
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What format are the 3d files in before you import them to Pepakura? You might be able to use an open source software like Blender to change the 3d model, would be much easier and more accurate way to visualize the changes needed, from my pov anyway as a 3d modeler.
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Old 09-08-2010, 08:30 AM
cfuruti cfuruti is offline
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Quote:
Originally Posted by tedparkes View Post
What format are the 3d files in before you import them to Pepakura? You might be able to use an open source software like Blender to change the 3d model, would be much easier and more accurate way to visualize the changes needed, from my pov anyway as a 3d modeler.
The point is, though I'm a casual Blender/POV-Ray user, I have neither the 3D model nor Pepakura Designer, so this is an exercise on what can be done purely in 2D.
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Old 09-08-2010, 08:37 AM
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tedparkes tedparkes is offline
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ah i misunderstood that, sorry.
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Old 09-08-2010, 10:26 AM
cfuruti cfuruti is offline
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Part 2 - 2D "modeling"

Now the real work begins, and I need an unfolded arm to play with. PDFCreator (PDFC) is a virtual printer for Windows; it can capture Pepakura Viewer (PV)'s output and save it as PDF, which I can load into Inkscape for Linux. Raster editors like the GIMP can import PDFs as well, but if PV is configured to print lines as "sharp" (vector), a vector tool like Inkscape can handle the black lines separately from the textures. This opens up interesting possibilities like
  • removing, modifying or moving the glue tabs
  • removing or making the folding lines less conspicuous
  • using face polygons as "paths" to clip or mask textures
Sadly, PV+PDFC's output requires some effort for this kind of job:
  1. the generated raster part is neither a big background layer, nor individual shapes for each part; rather, it's a matrix of square tiles, which often makes selecting elements cumbersome
  2. every single straight line is a separate element: to create a part's outline, one must select all relevant face edges, combine them into a path, then merge each pair of endpoints
  3. dashed lines become a series of short unrelated segments
[Hmmm, Inkscape natively saves as SVG, an open text format. An interesting exercise in XML could be writing an XSLT filter to regroup the raster tiles in a separate layer, fixing annoyance #1]

Here, loaded into Inkscape, is the section of the PDF relevant to the left arm. I rotated it to ease future alignment.
Extending parts without 3D tools - Whammy's Warhammer IIC-in_wh_multicam_armdesign1.jpg
This is a separate layer to where I moved the original vector lines, used only as reference and back-up. I cloned it as yet another layer, where the actual work will be done.
Extending parts without 3D tools - Whammy's Warhammer IIC-in_wh_multicam_armdesign2.jpg
Scaling up measurements form the schematic screenshot, I extended the upper end. I also created new tabs and moved the old ones to optimize gluing, accounting for reinforcement layers.
Extending parts without 3D tools - Whammy's Warhammer IIC-in_wh_multicam_armdesign3.jpg
Now a copy of the original "multicam" JPEG can be loaded as yet another Inkscape layer. After pasting, scaling, rotating and flipping, I get texture patches approximately aligned with the base skin layer. Notice:
  • clipping the patches is easy since I had previously combined lines into polygonal paths
  • with gradient masks, the clipped patches smoothly blend with the original texture, hiding seams
  • luckily I didn't need to create anything new, because the original JPEG had enough data to fill all the extra areas - except the very tip, which will be invisible when assembled
  • I patched over the round gray "hubcap", which is circular in the JPEG but elliptical in the model; this may have caused a small offset from adjacent faces, hopefully not noticeable
Extending parts without 3D tools - Whammy's Warhammer IIC-in_wh_multicam_armdesign4.jpg
I believe the hubcap problem, visible all over the model, is caused by Pepakura wrapping textures nonconformally over arbitrary faces. It is particularly annoying in obviously square or circular features like rivets and screwheads.
Finally, here's the completed left arm, with alignment marks for female joint orifices. Due to symmetry, the right counterpart is just a flip away.
Extending parts without 3D tools - Whammy's Warhammer IIC-in_wh_multicam_armdesign5.jpg
You might have noticed white hairline seams between the texture tiles. I don't know where's the problem, but a quick solution is duplicating the texture elements, adding a blur, moving to the background and clipping as usual.
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