8. Soft robotics¶

References & Inspiration¶

The backcountry is amazing. All those rocks arrange themselves so gorgeously. But they’re hard!? What if every time you sat down, the rocks felt cushioned?

I love to backpack. Even in the rain. Last time I was out in the wilderness, a friend lent me a rain skirt. It was a definite improvement over rain pants and easy to put on even with a big pack on your back. I loved it. But perhaps it could be improved with a soft robotic rainskirt seat...

Research & Learning¶

Robots: A robot is something that can sense, think, and act. When people imagine a robot, something hard and shiny comes to mind, like Boston Dynamic’s dancing dog, 3CPO from 2001 A Space Odyssey, and even giant robots that are used in warehouse automation. But they can also have soft, flexible systems. Soft robots need soft actuation.

Actuators: To actuate is to put into motion or action (think of the "act" in actuate). They are the parts that create motion.

Stimuli for soft actuators: Robots need a stimulus in order to act. Stimuli include:

Fluidic (air and liquid are both considered fluid)
Chemical
Biological
Thermal
Chemical

Stimuli for sensing include:

Physical signals: pressure, vibration, motion, touch
Chemical: olfaction and taste
Thermal: hot and cold
Electrophysiological: brain wave, cardiac, muscle
Light waves: vision and optic flow
Sound: hearing and ecolocation

Inflatables prototyping¶

Pneumatic-driven systems use pressurized air or gas to create motion and power machinery, unlike electric or hydraulic systems that use electricity or liquid. Energy conversion: Air is directed through valves and tubes to power actuators — the parts that act (create motion).

Heat press vinyl + baking paper¶

Method: Make a sandwich of two sheets of head-press vinyl with baking paper (parchment) to provide an air chamber in the middle.

General principles:

The design pattern affects the way inflatables move and take shape when inflated.
Heat and pressure is applied to seal two layers of fabric, with baking paper (parchment) in between to create an air chamber. Material is coated with a special plastic that melts when applied with heat.
Fold or shape becomes the actuation mechanism embedded in the object.
Material must be airtight and heat-sealable.

Instructions derived from Adriana Cabrera’s Manufacturing of Soft Robotics

The essential rules:

Connect all the chambers for the air/fluid to circulate
All the channels must be connected to the entrance of the air and the tube
Consider the sealing allowance in your design to isolate your pneumatic
Use thin vinyl when you want the inflatable to have thin, intricate shapes
Mirror the shape for asymmetric pieces

Steps for Heat press vinyl + baking paper method:

1. Preheat the heat press to about 120° - 140° C (248° – 284° fahrenheit) (you can also use an iron)
2. Cut out your top and bottom shapes with scissors or an Xacto blade. You can also use a vinyl cutter for more delicate or intricate pieces.
3. Cut out the baking paper shape for the air pocket, including an air tube inlet of 3/8" (9mm). Place it in the middle of the “sandwich.”
4. Place the three pieces on the heat press between two more sheets of baking paper.
5. Press the material for ~30 seconds. and wait for it to cool down.
6. Carefully remove the outer pieces of protective material from the vinyl, making sure not to rip the vinyl.
7. Insert the tube in the Inflatable and isolate it using a shrink tube and a lighter or heat gun.
8. Inflate and enjoy!

The first round of inflatables involved two methods: The manual heat press vinyl + baking paper sandwich method, and TPU welding with a laser cutter. We started with the manual method, testing various combinations with TPU material + waterproof fabric, and heat-press vinyl + waterproof fabric. I was encouraged by the tests that involved at least one side with waterproof fabric (eventually trying out this material for my final project — see Rain Skirt Cushionator, below!).

Next, I tried a spiral with waterproof fabric + baking paper + heat-press vinyl. How fun!

Then the same design with TPU + baking paper + TPU. This worked, as well.

When I initially tried to cut out the spiral in between the air channels, it failed to inflate. I fixed this by allowing for wider sealing margins. When I successfully unattached the spiral, it had surprising flower-like results!

TPU welding¶

TPU welding with a laser cutter yielded mixed results. It’s difficult to get the material to lay just right, and the air-tightness of the seams was hit and miss. It made me shy away from prototyping with this method, but would like to revisit when I have more time.

Tips for TPU welding:

File should contain layers for welding and cutting
Keep a 3/8" (9mm) opening for straw or tube
Adjust laser cutter settings (speed ~170-180)
Clean TPU material with alcohol
Two layers of TPU, weighted down
Turn on exhaust
Frame
Cut

Mold casting¶

Mold casting involves pouring silicone rubber into 3D printed top and bottom molds, and sealing them together with more silicone once dried.

Mold casting tips:

Silicone rubber, equal parts A & B
Stir well to cure
Fold so no bubbles or air pockets
Pour same location
Shake while curing (we used a generator)
4 hours, pour second half
Cure on flat surface

Glycerine and alginate bioplastics¶

We explored casting and sealing techniques for more sustainable materials, like gelatin bioplastics. It also involves a two-layer top and bottom approach. We tried one in a flower-shaped mold, and another as a flat sheet:

The edges of the second layer, once dry, are carefully "glued" to keep air from escaping:

Alginate inflatable bubble casting:

Hala Amer's sodium alginate tutorial, including recipe:

Instructions for alginate bubble casting:

1. Stretch base material on an embroidery hoop and spray with sodium chloride solution (10ml sodium chloride : 100ml water). This cures the outside.
2. Heat alginate solution and pour onto material
3. Spray with sodium chloride solution and wait about 30 seconds
4. Puncture side and insert tube to inflate
5. Use syringe to put sodium chloride solution inside
6. Lift and turn with solution inside, inflating occassionally to keep shape.

Hydrogels & 3D printing¶

This method allows you to create structures that self-actuates in liquids (swell in water). You 3D print the mold, but pause ¾ of the way up to fill the cavities with hydrogels, then finish printing. Use TPU 95A and set the bed temp to 2220.

Aqua-Morph is doing some inspiring work with hydrogels actuators.

3D printing in progress, below. The printer is stopped at this point, and hydrogels are added, then printing resumes. The walls of the 3D model are solid, and the top has a mesh design which allows hydrogels to come in contact with water, and inflate (just like a baby's diaper!). The print on the left will produces a twisting shape, the one on the right becomes a gripper.

These are results for a twisting and a gripper shape. You can see hydrogels leaking out of the top of the twister, so decreasing the openings in the top mesh of the 3D model is needed.

Assignment: Make a soft robotic sample, develop the pattern for the inflatable, and draw a sketch of the air flow.

Check out the weekly assignment here.

get inspired!

Check out and research alumni pages to betetr understand how to document and get inspired

materials comparison - Julija Karas - FabLab Bcn
Artistic intervention - Riley Cox - TextileLab Amsterdam
Zahia Albakri - CPF Makerspace
Viviane Labelle - EchoFab

Add your fav alumni's pages as references

Rain Skirt Cushinator: Process & workflow¶

Goal: Cushion your seat in the wilderness (or anywhere).

1. Materials¶

I chose to work with a combination of waterproof polyester and heat press vinyl. The polyester fabric felt softer to the touch and less rubbery than TPU, and I was encouraged by the early experiments. These three fabrics seem to fit the airtight and heat-sealable requirement. I couldn’t blow any air through them. The green one was labeled waterproof. To be sure, I did a quick test with each.

Test materials	Result
Green “waterproof” fabric + baking paper + heat-press vinyl	X The waterproof material immediately “popped” and it was easy to separate the two outer sides of the construction.
Coral fabric + baking paper + heat-press vinyl	√ Inflated and held air.
Pink fabric + baking paper + heat-press vinyl	√ Inflated and held air.

The pink material felt a bit more plasticky, so perhaps a better seal, but still more like fabric to the touch than TPU plastic. I chose it for the first larger test. Alas, at a large scale, it was clear the fabric could not adequately hold air.

Not to be deterred, I tried two more fabrics that seemed promising: One almost like a rain slicker, and the other like Tyvek — and matched them up with tried and true TPU + baking paper + heat press vinyl.

Results: The rain slicker-like material didn’t hold air well, and the Tyvek simply melted.

Of all the materials tested, tried and true TPU wins the day.

2. Pattern design variations¶

I tried two pattern variations based on the diamond hinge principle: The width to height aspect ratio of the diamond hinge determines the bending angle — wider diamonds produce more bend. Since time was of the essence, I proceeded with the diamond pattern on the left.

I cut the heat press vinyl pattern¹ with a Cricut Maker. The size of this prototype is limited by the size of the vinyl sheets, which were 10” x 12.” Ideally, the final cushion would be wider. The prototype component layers are heat-press vinyl, baking paper, and TPU.

Then I laser cut the baking paper layer². Since the baking paper is so light, the corners are weighted down and the cutting is paused half way through to remove stray pieces.

3. Results¶

Here is the heat-press vinyl + baking paper + TPU layers pressed, resulting uninflated and inflated cushioninator, and the inflation test video:

The final Rain Skirt Cushionator prototype:

4. Reflection & future pivots¶

The bend in the middle is much too subtle. Experiment with more variations in size, width, and distance.
This pneumatically-driven solution would ultimately be equipped with some smart sensing and auto-inflating when the hiker bends at at both hips to sit.
An outside fabric that is not translucent will better hide the internal cushion.
I’d like to do more material research and experimentation, starting with lightweight, waterproof ripstop nylon (like on a tent). Breathable waterproof fabrics like Goretex will not work, at least where the soft robotics device is located. I’d also like to try TPU coatings on other materials.
I wonder if there are other, more sustainable, materials to try, such as natural rubber latex.
Why stop at the Rain Skirt Cushionator? What if it's not raining? What if you're hiking on a hot and sunny day, or just out at the park sitting on a bench? Why not a Skort Cushionator (skirt + skorts = skort)?
What about a separate “bench” device all together that can be placed inside of whatever garment you are wearing? Stay tuned. :)

The Skort Cushionator in progress: