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What I learned building a Soft Robot

Are you ever so curious about a new technology that you want to try to build it yourself? Well, that’s how I often feel, and I’ve saved you the pain of trying to make a soft robot by doing it myself.

Soft robots use materials like urethane or flexible bodies to handle objects or move around, rather than actuating arms and claws. For industries like medicine and agriculture this technology opens the door to many robotics applications that would not be possible otherwise. That could mean handling delicate materials in an operating room or picking apples without crushing them.

** Jump ahead to the Construction Process **

The industry of soft robotics is still just in its beginning stages, valued near one billion dollars in 2020. Forecasts predict an annual growth rate of 40% from 2019 to 2020. For reference, the 3D printing industry is growing at a rate of 25% annually in 2020, while online grocery sales are growing at 75% annually.

Hopefully my experiment in building a soft robotic jellyfish can inspire you to make something even better and get some experience in this growing industry.

Starting the Journey

My initial plans grew from a lofty ambition. I saw an incredible free-swimming robotic jellyfish made at the University of Florida (YouTube) and got inspired. This robot uses a pump to suck in water, filling the arms, which extend and contract to swim around. A very cool project, but a little over my head for my introduction to soft robotics.

Lucky for me, I found much simpler instructions on Instructables, a terrific online resource for learning to make things yourself. More than 120,000 people have read the instructions since 2014, posted by Ben Finio, a Cornell engineering lecturer.

It always makes me feel better to know that someone else has done this before. The comments from other people who tried this gave me hope for success.

Pick a goal

I aimed to combine two interests; learn to build a soft robot and share information about jellyfish. In case you didn’t know, jellyfish have all sorts of incredible abilities. I always learn something better when I can interact with it, even a strange soft robot interpretation of it.

I would like to someday build a self-powered device, like the free-swimming jellyfish, but I accepted that this goal was a bit too far out for my first foray into soft robots. I chose to build a manually driven robot, which would propel when inflated by a little squeeze ball from a camera lens cleaner.

Work with what you’ve got

My final project had plenty of weaknesses, but I was proud of it. The interactive element did a lot to make up for the underwhelming gripper soft mechanism.

Ultimately the changing background lighting and LED ring drew people to the piece. When they stopped by, people seemed interested in the presentation and many of them asked additional questions about jellyfish. Goal accomplished!

What I learned

I think the biggest lesson for me was to expect construction to take a few tries. Even my fourth mold of the gripper arm did not work out quite right, and by then I was out of time. I started with my initial time estimate (“oh, this will take two tries”) and doubled it. Well, I guess I should triple my estimates for building things that are completely new to me.

I also learned to be gentler with prototypes. I have broken plenty of things in my life, as a general consumer, and also as a design engineer working on consumer electronics.

I’ve found that it takes me around three or four mistakes before I learn a lesson. This feels like too many! But changing my inherent nature is a challenge for another day.

My third prototype worked one time, so I quickly rigged it up to a bike pump. That was a terrible idea, and I promptly ruptured a hole in the side of the assembled part.

If you want to learn new facts about jellyfish, check the very end of the instructions.

”Will robots inherit the earth?
Yes, but they will be our children.”

— Marvin Minsky

Marvin Minsky, the computer scientist at MIT built the first neural network learning machine in 1951. He pushed the field of thinking about robots and what they might do for society. You can be certain that if he lived today he would be building things with soft robots.

Find Inspiration

I was initially inspired by this video of a free-swimming robotic jellyfish. I also partially followed directions that I found on Instructables. It always makes me feel better to know that someone else has done this before and the comments on the Instructables site gave me hope for success.

My soft robot construction process

I won’t claim to have built a perfect soft robot. Someone even commented on my YouTube video demonstration to say, “this is an utter failure. I can’t believe you even showed this off at an art show!” Or something like that – I am afraid that if I read it again I’ll never build anything else. Just kidding – someone’s always going to criticize, which is fine with me.

3D Model of the Mold

I used Fusion 360 to make a 3D model of the mold for my soft robot. The key was building a large enough pocket inside the mold so that air can fill the space and cause the fingers to bend. This took two iterations and I settled on a rib width of 3mm.

In case you want to print your own mold, you can find the 3D model STL file here (Dropbox link).

3D Printing

I printed my mold at the Public Library. I usually have access to a 3D printer either through work or friends, but having recently moved to San Diego I did not have many options. They were super helpful!

Casting

I used Smooth-On Ecoflex 00-30, which worked really well for me. I also bought the Ecoflex 00-30, which is a little stiffer, but I didn’t end up using it. They often sell these at art and hobby stores and I was able to walk over and purchase it from a small art store in my neighborhood. Of course, you can also buy this online, but support those little shops if you can!

Step 1 – cast the mold

First I thoroughly stirred the two epoxies together, which is crucial to get a thorough mix and remove as many bubbles as possible. Then I poured the viscous liquid into my mold to fill it almost to the top, but not quite overflowing. When I poured it over the top line it became much more difficult to remove without damaging the material.

Step 2 – cast the top surface

Then I poured a second layer that would end up being the top surface. This was just a big circle, but it needed to be larger than I had expected. On my first test run, I made the top surface too small and it did not cover the entire star pattern. The smaller top did not form a solid seal to cover the inner air pocket, which meant I could not push air in to cause the contraction as I wanted.

Step 3 – adhere them together

Before they fully cure, the top and bottom surfaces need to be stacked. I added some extra material around the perimeter of the start shape to ensure a good seal. I did not push them together at all and relied on gravity to do the work. I could see this being a problem if you made a very small mold and the shape with a cavity did not weigh enough to properly “smush” onto the surface below it.

Push in the air

This step was a little tricky but I used a lens cleaning tool for cameras plus a small diameter silicone tube. I cut a small incision in the back of the jellyfish, just over the center air pocket. I pushed the tube into the pocket and then sealed it up with a silicone glue (window caulk).

The Presentation Counts

I wanted to draw people in with this project so I embedded an LED ring in the jellyfish. I also added some RGB lights to the tank so that as a person walked closer to it the color changed from blue to red. I used a ping sensor (ultrasonic) to sense people getting close to the table, The goal was to get people’s attention and engage their curiosity.

The facts I shared about Jellyfish can be found below:

Why Jellyfish will take over the world

  • Jellyfish can survive in water with zero oxygen.
  • Box jellyfish, found in tropical regions, can range from millimeters to centimes in size and contain a toxin that is life-threatening to humans.
  • Portuguese Man O’War are made up of the different organisms – the bubble, the digestive tract and the tentacles.
  • Jellyfish have been found swimming in oil spills and their mucus actually helps to break down the oil.

More Resources

▶️ JenniFish on Youtube (2016)

A terrific free-swimming robotic jellyfish. Made by Jennifer Frame, Florida Atlantic University. I drooled over this video and still dream of someday building something that is half as cool as this.

📝 Air-Powered Soft Robotic Gripper – Instructables (2013)

Written by a lecturer at Cornell University, this tutorial has clout. This is where I found the details about materials and epoxies. The site also has a few other examples of soft robotics applications like walking and crawling.

▶️ How to build a robotic jellyfish (2018)

This is the video I made of the above project. Lots of lessons learned and I also show some clips of the project at the art showcase.

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