Introduction: FoldTronics: Creating 3D Objects With Integrated Electronics Using Foldable HoneyComb Structures
In this tutorial, we present FoldTronics, a 2D-cutting based fabrication technique to integrate electronics into 3D folded objects. The key idea is to cut and perforate a 2D sheet using a cutting plotter to make it foldable into a 3D honeycomb structure; before folding, users place the electronic components and circuitry onto the sheet.
The fabrication process only takes a few minutes enabling users to rapidly prototype functional interactive devices. The resulting objects are lightweight and rigid, thus allowing for weight-sensitive and force-sensitive applications. Due to the nature of honeycombs, created objects can be folded flat along one axis and thus can be efficiently transported in this compact form factor.
Aside from a paper cutting machine, you will need the following materials:
Step 1: Download FoldTronics Software
The design tool for FoldTronics is implemented in the 3D editor Rhino3D as a Grasshopper extension. Grasshopper directly exports the layers for the honeycomb sheet, insulating tape, and mountain/valley assembly. In addition, to generate the wiring, we implemented a ULP plugin to the electronic design software EAGLE, which exports the wiring layer – making the stack of layers complete.
The software for our design tool can be found on GitHub: https://github.com/eratoimf/foldtronics
You are going to need:
- The latest Rhino5 WIP
- Silhouette Studio
Step 2: Device Design Using the Software
To create the LED circuit, we start by creating a 3D model in the 3D editor Rhino3D for which we implemented our FoldTronics plugin. After creating the basic shape of the 3D model, we convert it into a honeycomb structure by pressing the "convert" button. As soon as the algorithm split the model into the honeycomb cells, the result is displayed in the 3D view.
We can now vary the resolution of the honeycomb using the provided slider to find the best trade-off between higher resolution and having enough space in the cells to house the LED, the battery, and the cross-cell circuit connector.
The resolution slider changes both the number of columns and the number of cells simultaneously because changing the resolution for columns and rows separately would cause the final shape to differ from the original shape.
To add the LED, battery, and cross-cell circuit connector, we select them from the list of components from the menu and add them by clicking the respective button. This automatically creates a 3D model of a box representing the size of the selected electronic component. We can now drag the LED and other electronic components to a location in the 3D volume. In case we accidentally place a component onto a fold or a non-valid cell, it is automatically relocated to the next valid cell.
- Import a 3D model in Rhinoceros.
- Run the "Grasshopper" and open "HoneycombConvert_8.gh".
- Select the model in Rhinoceros and right click a brep component and "Set one brep" on Grasshopper.
- Open "Remote Control Panel" of View of Grasshopper.
- Change the width of the cell using the slider.
- Convert model into a honeycomb structure and 2D cut data by clicking "Convert Honeycomb."
- Move the component (blue color) and change the size by "select components from this list." (still construction)
- Creating the component data by clicking "create components."
- Creating the 2D data by clicking "create cut data."
- Export cut lines with "selected objects" as AI file.
Step 3: Export Layers for Fabrication
Once we are done with placing the electronic components, we hit the "export" button to generate the layers for fabrication. On export, the 3D editor plugin creates all layers of the fabrication stack as 2D drawing files (.DXF file format) except the layer that contains the wiring, which will be created separately in a later step in the process.
To generate the missing wiring layer, users open the 2D file of the honeycomb structure in the electronic design software EAGLE and execute our custom EAGLE ULP plugin. The plugin generates a circuit board the size of the honeycomb pattern and then converts each colored square back into an electronic component (i.e. the LED, battery, and cross-cell circuit connector). With the electronic components already on the sheet, users can now build the schematic. Finally, users can use EAGLE’s auto-wiring function to create the full circuitry on the sheet finishing the last missing layer for fabrication.
** Currently, ULP plugin is under construction. You need to put the components manually.
Step 4: Fabrication, Assembly and Folding
Now we can start adding the generated layers together. To fabricate the layers, we only have to cut the 2D drawing of each layer (.DXF file format) in the right order using the cutting plotter.
Step 5: Cutting and Perforating the Base Sheet
We first insert the base sheet (PET plastic) into the cutter and cut and perforate it to create the mountain, valley, and slit lines as well as the markers for the electronic components. The FoldTronics process only perforates the sheet from the top and differentiates between mountain and valley lines using separate visual notations (dotted lines for mountains vs. dashed lines for valleys) since they require folding into opposing directions later on. Alternatively, the FoldTronics process can also perforate the sheet from both sides, i.e. perforate the mountains from the top and valleys from the bottom, however, this requires re-inserting the sheet into the cutting plotter.
While all the slits are cut through, the outline of the honeycomb is only perforated to keep it connected to the main sheet, which allows us to further process the sheet with the cutting plotter in the next steps. Finally, the areas where electronic components will be soldered on are also perforated to make it easier to find out which component goes where.
For the objects used in this paper, we use PET plastic sheets, thickness 0.1mm and cut the sheets with a cutting plotter (model: Silhouette Portrait, settings cutting: blade 0.2mm, speed 2cm/s, force 10, settings perforating: blade 0.2mm, speed 2cm/s, force 6).
Step 6: Placing the Wiring With Copper Tape
Next, we place a layer of one-sided copper tape (thickness: 0.07mm) across the entire sheet. We put the sheet back into the cutting plotter with the copper side up, then execute the file to cut out the shape of the wires which is configured to make sure to not cut into the base sheet (cutting settings: blade 0.2mm, speed 2cm/s, force 13). Afterward, we peel off the copper tape that is not part of the wiring.
Step 7: Insulating Sheet
In order to prevent any short circuiting from wires touching after folding the base sheet, we next add an insulating layer. For this, we place a layer of regular non-conductive tape across the entire sheet (thickness: 0.08mm). We put the sheet back into the cutting plotter, which removes the insulating tape only in those areas that have wire ends that either will be connected to electronic components or that use our novel cross cell circuit connector. We use the cutting settings: blade 0.1mm, speed 2cm/s, force 4.
Step 8: Glue Mountains/Valleys to Hold After Folding
In the next step, we apply a layer of regular double-sided tape to the sheet on both its bottom and its top. The double-sided tape is used to connect the valleys and mountains that hold the honeycomb structure together after folding (mountains get glued from the top of the sheets while valleys get glued from the bottom). After inserting the sheet into the cutting plotter, the double-sided tape is cut out in all areas that are not supposed to be taped together (cutting settings: blade 0.2mm, speed 2cm/s, force 6). In addition, for taped valleys/mountains that also carry a cross-cell circuit connector, the cutting plotter cuts out the areas needed for the electronic connections. After cutting both sides, we peel off the remaining double-sided tape.
Step 9: Soldering
In a final step before soldering, we now cut off the honeycomb pattern to disconnect it from the sheet. Next, we solder the electronic components (LED, battery) onto the wires using a soldering iron. If the components are small and hard to solder, we can also use solder paste as an alternative. Since soldering the cross-cell circuit connector is difficult, we use double-sided conductive tape to create the connection.
Step 10: Folding
We now fold the honeycomb together.
Step 11: Light It Up!
Your circuit is ready!