Merge pull request #154 from orionrobots/openscad-article

Convert some old screenshots, and journal notes into a post

Author: dannystaple

Diff for: content/2018/03/02-ldraw-to-scad/ldraw-to-scad.md

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+---
+title: LDraw to OpenSCAD Tool
+tags: [lego ldraw, lego technic, lego robotics, lego rcx, lego mindstorms, python programming, openscad, lego cad, robotics cad, 3d cad, cad, cad-software]
+date: 2018-03-02
+thumbnail: content/2018/03/02-ldraw-to-scad/openscad-adder-subtractor-buggy.png
+---
+I wanted to look at some of my older Lego robotics projects and work again, and perhaps render or interact with them in a different way. I've been using OpenSCAD for a while, and I wanted to see if I could convert some of my LDraw files to OpenSCAD. This was also related to adding Lego assemblies to non-Lego robots for some modular robot designs.
+
+I wanted to also go further, and animate my Lego builds.
+
+I build a Python based tool to manage this, and I'm quite pleased with the results.
+
+## Getting it
+
+The project is all Open source, on [GitHub](https://github.com/orionrobots/ldraw-to-scad). It requires Python3 to run.
+
+You will also need an LDraw library, and OpenSCAD installed.
+
+## What features does it have?
+
+This converts the LDRaw model to an OpenSCAD model.
+The submodules and parts become OpenSCAD modules. The comments are also converted to OpenSCAD comments.
+Colour files are also supported.
+
+It's not quick, as it does need to go through the library of parts. It's also not perfect, as it doesn't handle all the LDraw features.
+
+## Do you have screenshots?
+
+Yes, a few models that have come from the Orionrobots archives are here, in OpenSCAD! These are before the colour fixes.
+
+### 4744 Lego Brick
+
+![4744 Lego Brick](/2018/03/02-ldraw-to-scad/openscad-4744-lego-brick.png)
+
+The first thing was to get a single Lego brick working. In the LDraw world this is already multiple files, making use of the primitives. This is a simple brick, but it's a good test.
+
+The code shows the named primitives and subparts being sensible named modules in the OpenSCAD code, and the LDraw comments being preserved as OpenSCAD comments.
+
+### RCX Double sensor pad
+
+![RCX Double sensor pad](/2018/03/02-ldraw-to-scad/openscad-rcx-double-sensor-pad.png)
+
+This model was a simple two sided bumper for a Lego RCX based robot buggy. It contained multiple elements, so was a good test over the single brick.
+
+It is using a reference colour here, as the colour files are not yet fully implemented. It's clear from the render that the parts, including features like studs are represented.
+
+### Lego Adder Subtractor Buggy
+
+![Lego Adder Subtractor Buggy](/2018/03/02-ldraw-to-scad/openscad-adder-subtractor-buggy.png)
+
+This is the [Adder Subtractor buggy](wiki/adder_subtractor_drive.html), a Lego RCX based robot that uses the adder subtractor drive for steering - it mechanically eliminates some of the motor differences, so the robot can drive straight.
+
+This complex demonstration is a larger assembly with multiple LDraw parts files, a multi-part-data or MPD file. It took 26 seconds to render in OpenSCAD, as it's quite a large file.
+
+It may be possible to optimise the output and flatten some of the primitives in a later version - but at this point, it is all like-for-like. The OpenSCAD file has 38k lines of code!
+
+## Ideas for improvement
+
+We could consider substituting primitives for OpenSCAD primitives, like stud curves that are approximated by lines being substituted for real curves.
+
+Eg, for the 4-4cyli ldraw primitive something like this:
+
+```openscad
+$fn=20; 
+rotate([-90, 0, 0]) 
+{ 
+    render(convexity = 2) difference() {
+        cylinder(1, r=1, [0, 0, 0], center=true);
+        cylinder(1.2, r=0.9, [0, 0, 0], center=true);
+    };
+};  
+```
+
+This needs testing, and makes the project more complex.
+
+## What's next?
+
+This project was a bit of a test, and for me to specifically get an animation working. I don't currently have long term plans, however, members of the github community have taken an interest in this, and I am happy to support them improving this tool!
+
+However, I've also found a [Blender export/importer for LDraw](https://github.com/TobyLobster/ImportLDraw), which I will look at next as it may be a good fit for me getting animations.
+
+
+## Helpful links for building this
+
+- [The OpenSCAD cheatsheet](https://openscad.org/cheatsheet/) incredibly helpful when building this. OpenSCAD is a very interesting CAD system, especially for programmers. This LDraw-to-scad project is effectively a transpiler for it.
+- [The LDraw file format](https://www.ldraw.org/article/218.html) - this is the file format I am converting from.
+- [LDraw multi-part files](https://www.ldraw.org/article/47.html) - The multi part files are a further specification.
+- [OpenSCAD Includes](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Include_Statement) - this may be a way to reduce the duplication. Currently it generates a single big file. It could generate a library.