11. Soft robotics#

This week we learned about soft robotics and made inflatable…things out of different materials, and using different techniques!

What I Made#

I made a couple of different inflatables with varying degrees of success:

Some were made by hand, using baking paper and heat transfer vinyl:

Two others were also made with the same materials, but using patterns designed in Rhino and laser cut:

Rhino-Grasshopper patterns

And I also made one out of silicone, using a shape made in Grasshopper/Rhino and cast in an acrylic mould:

Thermo-Adhesive vinyl, the low tech way: drawing and cutting by hand#

We started off by using thermo-adhesive vinyl, aka heat transfer vinyl, aka the stuff you can use to stick graphics onto t-shirts, to make simple inflatables. It works like this:

How it works#

inflatable template

handmade inflatable process

First inflatable - simple geometric shape#

This was my first inflatable:

Cutting some of the excess vinyl around the air channels allowed it to move differently:

Second inflatable: triple spiral#

Then I made a triple spiral shape:

And cut around the edges of the spiral:

And then cut around the individual spirals, which made this nice effect:

I made digital files for the two shapes, which can be downloaded at the end of this page.

Heat transfer vinyl, the high tech way: digital drawings and laser cutting#

You can also use the same method with more complex shapes, using digital design sofware like Illustrator or Rhino, and laser cutting the air flow pattern.

Circular voronoi pattern#

Designing the pattern#

I used Grasshopper to generate a voronoi pattern (I’ve written more about the details of this in my Computational Couture documentation). Then in Rhino I used the scale function to move the individual sections of the pattern away from each other (creating space in between them for air to flow). Then I drew a circle around the shape, and added a rectangular section to use as a channel for air to enter the shape.

Grasshopper - creating the pattern

circular voronoi pattern

Laser cutting and assembling#

I laser cut the air flow pattern out of paper (settings: speed 100, power 15), then placed it between two sheets of vinyl and ironed them together. Then I cut around the outside with scissors.

collage of process

The pattern I designed has lots of small pieces in the middle of it, and quite narrow air channels, which I thought might be a bit too delicate to work, but I wanted to give it a try. It did turn out to be too fragile - when I blew into the shape with a straw, the delicate inner air passages popped. It was fun to try though!

Sort-of-gripper-type-pattern#

I also cut a different shape and tried making a slit for the air flow in the centre.

Designing the pattern#

Again, I used Grasshopper to create a voronoi pattern, and baked both the voronoi pattern AND the points used to generate it into Rhino. Then I used the Scale function, with the option ‘Rigid’ set to ‘yes’ - this moves the individual parts of the shape away from each other (creating space in between them) instead of just making the whole thing bigger.

Then I used the ‘curve through points’ function to create a curve along the middle of each ‘leg’ of the pattern:

Then I imported the pattern into Illustrator. I increased the stroke weight of the curve to make it thicker, then went to Tools -> Path -> Outline Stroke. Then I united the outlined curve with the the rest of the shape, and I had my airflow pattern!

Looking at the pattern, I decided that the sections of the air flow would actually be too small for air to flow into them well. So I imported the file into Illustrator and edited the path to unite some of the sections together. I also replaced some of the very small parts in the centre with a larger middle section:

illustrator image

This is what I ended up with:

edited pattern

Laser cutting and assembling#

I cut this out of baking paper on the laser cutter with the same settings as before.

Then I got two sheets of vinyl, and in the centre of one I cut a small slit and inserted a thin rectangle of baking paper into it. This was an attempt at having the air enter through the centre of the shape, to see what would happen.

paper to inflatable

Then I pressed vinyl with an iron, as before, and tried inflating it with a straw. Unfortunately, I the slit I cut for the air to enter was a bit too wide, so the shape doesn’t inflate well as a whole.

Cutting out the shape from the vinyl sheet allowed for a bit more inflation and movement:

It’s also possible to inflate some of the ‘legs’ individually by how the straw is angled:

Silicone Moulding#

The other technique I tried was making a mould for a silicone soft robot!

Design#

For the design of my mould, I took a voronoi pattern I had previously created in Rhino, similar to the one I made in the previous section of this documentation. I separated out one of the ‘legs’ of the pattern, then drew an outline around it, created a curve through the centre of the shape, and offset that curve to create the shape on the right in the image below:

shape progression

To make a mould of this shape out of acrylic, three separate parts are needed:

https://gitlab.fabcloud.org/academany/fabricademy/2019/students/jessica.stanley/raw/master/docs/images/week11/softrobot_mould.PNG

Making the acrylic mould#

I tried exporting my mould design straight from Rhino to dxf, but wasn’t able to figure out the right settings to get that to work with the laser cutter software. So I exported the file as an Illustrator file, then re-opened it in Illustrator, and saved as an Illustrator CS2 file (with all optional boxes unchecked).

We had a long scrap piece of 3mm acrylic in the lab which was big enough to cut out my mould. I used: - Speed 80, power 25 to engrave the shape on the bottom layer - Speed 25, power 80 to cut out everything else

At this point I apparently forgot to take pictures, but I glued my mould together with superglue.

Casting the silicone#

Next it was time for silicone casting! At TextileLab Amsterdam we used Ecoflex to make our moulds.

I needed to figure out the volume of my mould, to estimate the amount of silicone I’d need. the easiest way to do this was to put it on a weighing scales, and fill it with water. As the density of water is approximately 1 kg/L, this means the weight (ok strictly speaking, the mass) of the water is the same as its volume.

The only downside to this method is that you need to dry the mould thoroughly afterwards, as silicone and water don’t mix well :)

Next: - Spray the mould well with mould release, using a paintbrush to make sure all small parts and corners are coated - Mix the silicone as per manufacturer’s instructions, stirring it slowly to avoid bubbles - Pour the mixed silicone into the mould!

I also cast a thin layer of silicone onto a piece of thin fabric, to later stick on to my moulded piece, and form my soft robot!

Unmoulding and finishing#

This is what my mould looked like when dry (it dries in about 4 hours, but was left overnight)

dried and ready for unmoulding

Unmoulding it was a 50% satisfying 50% nerve-wracking experience:

I mixed a small amount of silicone and painted it onto the open side of my mould, then stuck it on top of the fabric/silicone layer and left that to set for a couple of hours. Then I cut around the edges using a scissors, and used a large embroidery needle to create a hole at the large end so I could stick in a syringe and inflate it.

finishing up

So, does it work? It kind of inflates, but not super well. I think that the fabric/textile layer wasn’t even enough, and I might have also made the central air channel too narrow. In retrospect I think it might have been a good idea to try the design with baking paper and vinyl first, to see it if would work, before going through the whole process of making a mould.

Files#