2. Computer-Aided Design (CAD)#

In this unit:

• introduction to some CAD softwares
• process of designing a flexlink object
• license

CAD#

there exist many software of Computer-Aided Design. 2D design and 3D design. Here I will present some 3D CAD software and make a flexlink object to demonstrate the capabilities of such software.

sofwares#

Some software are FOSS (free open source software) and it is best to start leading with them. Because it can be pretty frustrating to switch tool from a non-intuitive and less complete one to a proprietary intuitive and with a complete set of tools.

• OpenSCAD is a free software for creating solid 3D CAD models. It is not an interactive modeler, but rather a 3D-compiler. OpenSCAD reads from a script and renders a 3D model from it. This gives you full control over the modeling process and enables you to easily change any step or make designs that are defined by configurable parameters.

• FreeCAD is a general-purpose parametric 3D CAD modeler. Parametric modeling allows you to easily modify your design by going back into your model history and changing its parameters. FreeCAD is open-source and highly customizable, scriptable, and extensible. FreeCAD is multiplatform, and reads and writes many open file formats such as STEP, IGES, STL, SVG, DXF, OBJ, IFC, DAE, and many others.

• Fusion 360 is a cloud-based 3D CAD tool. It combines industrial and mechanical design, simulation, collaboration, and machining. Fusion 360 is developed by Autodesk and is a subscription-based software. It is available for free for students, educators, and startups meeting certain criteria.

• Solidworks Extremely complete software with an initial release in 1995 and developed by Dassault Systèmes. It only works on Windows OS and licenses are expensive.

Modeling a FlexLinks object#

For this unit I will use Fusion 360 because I already know how to use it and going back to a more basic and less intuitive software like FreeCAD is difficult.

The object is a trebuchet-catapult. Due to the unit 3, modifications had to be made in order to reinforce the catapult and making it 3D printable. These modifications are not included here.

First sketch of the object#

To know how to start a 3D drawing the first thing is to make a rough idea of the object.

This sketch show that there will not be many independent pieces. It could be possible to print it whole.

Test of flexlink#

I didn’t know to what extent 3D printed PLA could bend. The work of a classmate showed me that a spiral spring work pretty well.

It showed that it is perfectly functional and that it has to be printer horizontally to increase the solidity. The reason behind this is that the connections between the plastic filament are not under tension.

Thanks to Eva Dubar for the spring in openSCAD.

drawing in Fusion 360#

• All body or body part (unless using a more complex function) start with a sketch. A sketch is always on a plan (origin or plane made out of a body part).
• It is better to fully constraint a sketch (coincidence, distances, …) so the object is more “stable”.
• It is possible to mirror body and sketch. It reduces the amount of part to draw “by hand”.

• Once the support of the catapult is done, the moving part can be placed. It includes the bar and launcher as well as the spiral spring.
• To make a spiral in fusion 360, select coil and then spiral for the type. The preview shows the result of the parameters in real time. If there is no preview, it means that some parameters of the spiral are in competition. Tweaks around to find out the ones.

• The half of the object can now be mirrored

Verifying the final object#

Now that the object is finished, we can print it to make sure it is functionnal. This module show how to print it.

Licences#

This work is under CC BY-SA license.

• BY: credit must be given to the creator.
• SA: Adaptations must be shared under the same terms.

More on the different CC licences here.