Flow(er) of life

Flow(er) of life, soft robotic (Fabricademy, FabTextiles, Fab Lab Barcelona, 2018)


Project : Create a soft robotic structure made of silicone and acting like a breathing mecanisme.


Process :
(1) Design on Rhinoceros the silicone mold
(2) 3D print the mold
(3) Cast the silicone
(4) Test the first prototype
(5) Make a second prototype
(6) Build the pompe circuit


Material :
- Rhinoceros software
- Cura software
- 3d printer machine + PLA filament or FilaFlex
- silicone
- vacuum (for taking out the silicone bubbles)
- scale + pot + spoon/wood stick
- plastic mold
- scissors
- a surgery needle + a rubber tube + an electric pump
- a computer
- an Arduino + Arduino software
- jumping cables + crocodiles clips


(1) Desgin on Rhincceros the silicone mold After thinking about the breathing system I needed to find the adapted shape for doing it. I started to design a flower with six petals that can be repated to infinity, creating a pattern with triangular holes. When air is introduced inside the structure, each petals of the flowers expend, reducing slowly the size of the holes until blocking them completely. Designing this pattern I realized that it was looking like the flower of life geometry shape. In some old spiritual religions and beliefs, this perfect flower shape was representing fundamental aspects of space and time. A shape that used to intrigued Leonardo da Vinci for its facinating mathematicals proprieties found in Nature.


(2) 3D print the mold
ON THE COMPUTER Once you finish your 3d model on Rhino, save it in a STL file (an abbreviation of "stereolithography", printing layer by layer). Open your STL file in Cura and set up your 3d print machine. I printed this 3d model on a Reprap with a 0,6 extruder. I used white PLA of 3mm diameter with a 200°C melting point. I programmed a quality layer of 0,2 mm with a regular speed of 60 mm/s. For this silicone mold, it would have been wise to print with filaflex and make easier the demolding stage. In this case, you would of increase the printing tempreature to 245°C and decrease the printing speed to 30 mm/s.
ON THE PRINTER Click on the main button, select Prepare -> Preheat -> PLA, then go back to the main page and select Prepare -> Motion and check the X and Y axis. You can also move the Z axis to the top for changing the filament and extrude it to be ready to start.


(3) Cast the silicone
Make silicone is not complicated. You just need to buy the preparations to make it, have a vaccum, a scale, a clean pot and a wooden stick or a spatula. In the Fab Lab Barcelona, we use the Smooth-On series like the Ecoflex or the Dragon skin for exemple. For my prototype I used both and I didn’t really saw any differences between the two of them. Both Ecoflex and Dragon Skin are strong and flexible. It’s possible to stretch them many times and they will go back to their original forms without tearing or deforming. The best part is that they are both certified skin safe, so if you forgot to put gloves it’s completely safe.
The preparation for Ecoflex and Dragon Skin is the same : In a clean pot mix the same quantity of part A and part B, then mix the liquid with a clean wood stick. You will normally see bubbles in your mixture. On the website they say that’s it’s not necessary to use a vaccum for the Dragon skin, but if you look carefully there is bubbles like in the Ecoflex so if you want to make a perfect mold it’s better to use the vaccum as well. Pour the liquid into the 3d print mold you’ve made, then vaccum it. When you finished to take all the air out of the mixture. Put your silicone mold to dry on a flat surface. Wait 2 or 3 hours before taking out the cast or you can also make it dry faster in the oven. Don’t forget to cast an other silicone flat layer for closing the prototype at the end.


(4) Test the first prototype
After few hours of drying, the cast is ready to remove from the 3d print mold. Good news, the silicone cast is perfect ! Bad news, I’ve just realized that i’ve made a mistake designing the mold In my 3d model on Rhino I forgot to extrude the triangles more than the border line. When i cast the silicone I blocked the triangles that was suppose to be holes ! After that, I tried to fix my error by cutting with a scalpel each triangle one by one.
Next, I have to cover my first prototype layer with an other dry silicone layer. I closed the two layers with liquid silicone. After the drying process, start to cut the triangles holes on the other flat silicone part. This part was more difficult than the first one because more thick and I was scared to make involontary holes inside the petals and ruin the prototype. Unfortunately, I probably made a bad hole inside my prototype because at the end it didn’t inflate. But it also could be the lack of power of the air pump I had. My sample was pretty big for those kind of air pump. For this reason, I decided to draw a diagram to explain what should have happened if the mecanism had worked.


(5) Make a second prototype
Because my first prototype didn’t work I decided to make a smaller version and test the mecanism on only one flower. So let’s go back to Rhino, Cura, the 3d print room, the silicone casting.... Youpiiii !
This time I decided to 3d print two molding parts : the central flower and the closing sides that I will use 2 times, one for each side. At the end of the silicone molding I get 3 parts : the top part (1), the middle part (2) and the bottom part (3).
For assembling the 3 pieces together, I did it in two steps : The top with the middle part and the top/middle with the bottom part. I prepared a small quantity of silicone to glue the different parts. I used the 3d print triangular pieces as a structure for holding in the right position the parts together.


(6) Build the pompe circuit
If you want to controle the speed, the time or the frequency of your pump motor you need to build an Arduino circuit and code some commands in the Arduino software. You can learn more about it online in a nice Adafruit tutoriel (link at the end of the page).
In my case, I just wanted to test if my silicone cast will inflate correctly. Because I didn’t have a particulary task to ask to my pump I just used the Arduino as a battery and connected the electric pump on it. I did a hole on the side of one petal of my flower and introduced inside the rubber tube of the pump. Surprise ! It worked ! I’ve made my first soft robot ! And I have two videos to prove it !