[Learning] 3D Printing and FEA

Tl;DR

You just need .STL to bring designs to the real world

Intro

• WHY Im writting this post: bc this power staging makes a mess and i want to put some order to the table
• WHAT Ive learnt with it: Ive ended up sending for manufacturing STLs for the first time a fpv dron stand

Summer is almost gone…

What are you waiting for?

Design Hello World

Its not the time to talk about design for manufacturing (yet).

Design Files 101

Its all about .STL, .Blend and FCstd files

And about getting these installed:

#choco install openscad

Blender can do what?

choco install blender --version=4.2.2 -y
#  choco info blender 
#brew install --cask blender #this got me the latest 5.1

What about Freecad?

freecad

Selfhosted OSS 3DPrinting

Every program on your list is an open-source software (OSS), self-hostable tool designed specifically for the 3D printing ecosystem.

Thanks to: https://selfh.st/apps/?search=3d

Typical Self-Hosted 3D Printing Stack

Most homelab makers combine these into a unified workflow:

1. Model Storage & Organization: Manyfold stores, tags, and previews your 3D files (STLs, 3MFs).
2. Filament Tracking: Spoolman tracks remaining spool weights, colors, and vendors.
3. Printer Control & Execution: OctoPrint (or Klipper + Moonraker) receives sliced G-code, monitors temps, and communicates with Spoolman.
4. Safety & AI Monitoring: Obico Server taps into OctoPrint’s webcam feed to catch print failures (spaghetti/detachment) and pause the job automatically.

People is really creative online:

• https://www.thingiverse.com/thing:5965826 Minimalistic Motorized Roller Blinds - NEMA 17 stepper motor gear

Conclusions

Wherever you see price = cost + margin, you are looking to a commodity

For the ones that dont want to read an ebook neither to pay consulting or the DFY…

I offered a 1 to many free session, aka Webinar.

At my schedule convenience. And where I try to sell you services, ofc.

FAQ

Where to get Models

1. thingyverse
2. makerworld

Where to get them printed

I recently got to know that pcbway can estimate the cost and send you plastic and even metal 3dprints :O

I got my first 3dprints done like so

My First 3dPrint

Thanks to https://aetherfpv.com/pages/gravity-drone-stand I got a STL with a fantastic design that brings a dron stand

1. via https://drukex.pl/en/pricing/#wycena-form I got my first quote

cd ./poc/blender/dron-standing #https://github.com/JAlcocerT/3Design
make inspect-print-ready-quote
make inspect-quote-8

The estimated price for FDM 3D printing starts from just PLN 0.9 per gram of the finished print. For larger quantities of identical parts, the cost may drop to approximately PLN 0.7 per gram.

The editable scene and reproducible generator are also included:

• Blender scene (reference/ original_assembly_mechanism_15s.blend)

• Animation script (animate_original_assembly.py)

make animate-original-assembly
make open-original-animation
make animate-original-assembly-detail-180
make open-original-animation-detail-180

2. I also tried an ordered from: https://drukarex.pl/

Materiał PETG, warstwa 0,20 mm, 4 ścianki, wypełnienie 30%

3. Also got to know that there is an agregator https://craftcloud3d.com/ which can also print in metals like aluminum or titanium (they also have cnc machining and molding - crazy that this can be some kind of manufacturing as a service!)

And it worked

yup, the dji tello looks good with the stand:

Improvements

So for v102, we would replace: four-finger snap-fit collar → two-jaw snap-fit collar

Yep, i snapped one!

it is not a rack-and-pinion.

The best name is a rack-and-pawl ratchet—more broadly, a discrete ratcheting linkage.

The toothed long rod is the rack; the arm/slider engagement acts as the locking pawl/detent.

There is no rotating circular gear (a pinion) driving the rack.

That part was strong enough thought

And i made a second order

FEM x Calculix x Beso

Skipping my oss mbsd framework this time, just curious to see how stress flow through the 3d print I got:

You can get FEM/FEA done with Calculix/Beso as I captured at these learnings notes

+—————————————————————————————–+ | INPUT GEOMETRY | | Watertight STLs | +—————————————————————————————–+ │ ▼ +—————————————————————————————–+ | 1. GEOMETRY PROCESSING FreeCAD 1.1.1 (Snap) | | Converts STL skins to faceted BRep solids | +—————————————————————————————–+ │ ▼ +—————————————————————————————–+ | 2. MESHING & OPTIMIZATION Gmsh 4.15.2 (Python venv) | | Linear tetrahedrons + Netgen volume optimization | +—————————————————————————————–+ │ ▼ +—————————————————————————————–+ | 3. SOLVER CalculiX 2.21 + SPOOLES (Unpacked in tools/) | | Linear static analysis using C3D4 elements | +—————————————————————————————–+ │ ▼ +—————————————————————————————–+ | 4. POST-PROCESSING MeshIO 5.3.5 & NumPy 2.5.3 | | Extract FRD fields; write summary.json & VTU exports | +—————————————————————————————–+ │ ▼ +—————————————————————————————–+ | 5. VISUALIZATION Blender 5.1.2 & Pillow | | Surface stress heatmaps in assembly context | +—————————————————————————————–+

Run it with:

cd /home/jalcocert/Desktop/poc/blender/dron-standing-fea
./run-fea.sh cases/frame-screen.json
./run-fea.sh cases/frame-screen-fine.json

Built and tested a fully local FEA pipeline:

• Verified all eight printable STLs are watertight.
• Installed project-local Gmsh and CalculiX—no system/admin installation needed.
• Used FreeCAD to reconstruct the STL as a faceted BRep.
• Created automatic tetrahedral meshes with quality reporting.
• Applied a placeholder 19.62 N load—equivalent to 2 kg—to the isolated stand frame.
• Solved coarse and fine meshes and exported viewable VTU results.

Results:

• Coarse: 3.08 mm displacement, 27.65 MPa peak stress.
• Fine: 5.96 mm displacement, 41.35 MPa peak stress.

Because the values changed substantially, the model is not converged.

The software workflow works, but this particular test is only a pipeline demonstration—not validation of the complete assembled stand.

Blend x STL x FCstd

An STL file (short for Stereolithography or Standard Tessellation Language) is a standard 3D file format that represents the surface geometry of a 3D object using a collection of connected triangles (a polygon mesh).

It contains no color, texture, material properties, scale units, or construction history—only the 3D coordinates ($X, Y, Z$) of triangle vertices and surface normal vectors defining inside versus outside.

Because of its simplicity, it is the universal standard for 3D printing slicers and CAM software.

Think of an STL as a flattened, printed PDF, while a FreeCAD file is a parametric blueprint with dimensions, and a Blender file is a complete film/art studio project.

1. How a Cylinder is Handled

• FreeCAD: Stores a cylinder as a circle definition with a precise mathematical radius $r$ extruded to a height $h$. If you measure it, it has a perfectly continuous curve.
• Blender: Typically models it as an $N$-sided polygon cylinder (e.g., 32 sides) with top and bottom caps. You can smooth the shading visually or subdivide it dynamically.
• STL: Converts the cylinder into hundreds of tiny flat triangles. Curved surfaces lose their mathematical precision and become a mosaic of flat planes.

2. The Workflow Relationship

You rarely design in an STL. Instead, you work in FreeCAD or Blender, and export to STL as the final step:

[FreeCAD]  (Precision mechanical design) ──┐
                                          ├──> Export as .STL ──> [Slicer] ──> [3D Printer]
[Blender]  (Organic sculpting / art)     ──┘

• If you need to edit an STL later, opening it back up in FreeCAD or Blender turns the model into a “dumb” triangle mesh—the original sketches, dimensions, and modifiers are permanently lost.

OpenSCAD is fundamentally different in how you create models: it is a programmer’s solid 3D CAD modeler.

Instead of an interactive visual workspace where you click, draw sketches, or drag vertices with a mouse, OpenSCAD has no interactive modeling viewport.

You write pure code in a script file (.scad), compile it, and the software renders the resulting 3D geometry using Constructive Solid Geometry (CSG).

• STL (.stl): The printed PDF.
• Blender (.blend): Photoshop / Maya (artistic manipulation, polygons, sculpting, animation).
• FreeCAD (.FCStd): AutoCAD / SolidWorks (visual GUI, 2D constraint sketches, feature tree).
• OpenSCAD (.scad): The raw source code (C++/Python style code that compiles into a 3D object).