Make a Robotic Balloon Muscle
30-60 min
Ages 8+
What Will You Make?
If you’ve seen the Disney hit Big Hero 6 and its star Baymax, you know that soft, inflatable robots are all the rage. Inflatable robots and robotic parts are cheap, lightweight, strong, and collapsible, making them easy to store or carry. And inflatable air muscles allow robots to move in a more natural way than gears and motors.
This project is based on a twisty balloon air muscle created by a Brigham Young University mechanical engineering student named Wyatt Felt, and adds a few twists of its own. It opens and closes a Sarrus linkage, a pair of hinges set at right angles to one another, and includes a built-in release valve mechanism. It’s easy to put together and great for showing kids (or adults) how air pressure can be used to actuate robot parts.
The Robotic Balloon Muscle project is adapted from Kathy Ceceri’s new book Making Simple Robots: 2nd Edition published by Maker Media.
What Will You Learn?
This build doesn’t require anything fancy. Just make sure you have extra balloons on hand — they tend to pop!
You will learn to blow up, twist and tie balloons as you explore pneumatics — a branch of engineering that makes use of gas or pressurized air.
Blow Up Two Balloons
Step 1
Use the hand pump to inflate two balloons, leaving about 4 to 5 inches (10 to 12 cm) uniflated at the end. This is known as the tip of the balloon.
Helpful hint: Before inflating a balloon, stretch it lengthwise a few times.
Step 2
Remove the pump and let out a little air (known in the business as burping the balloon). This bit of slack makes it easier to twist the balloon without popping it. Tie the neck of the balloon in a knot to seal it.
Connect the Balloons
Step 1
Take one of the balloons and pinch it gently about 3 inches (8 cm) from the knot. Twist it around three times.
Step 2
Do the same to the other balloon, then connect the two balloons by twisting them together where they are already twisted.
Make a Hinge in Each Balloon
Step 1
To make a hinge in the first balloon, bend it in half. At the bend, pinch a golf-ball-sized segment in your fingers.
Step 2
Twist it around three times, spinning it like a dial. Then circle it around the balloon itself until it reaches its starting point.
Step 3
The hinge should look like a knee sticking out in front. Do the same with the other balloon.
Tie the Tips of the Balloons Together and Insert the Tubing
Step 1
Tie the tips of the balloons together using the uninflated extra rubber. Tie another knot about half an inch (1 cm) above the first. The balloons will form a diamond shape with the hinges in the middle.
Step 2
Now take the 10-inch (25 cm) piece of plastic tubing and the scissors or an art knife. Make a release valve in the tubing by cutting a small slit about halfway down. Don’t let it go more than partway through the tubing. You should be able to bend the tubing back to open the slit without tearing the tubing.
Take a piece of electrical tape about 2 inches (5 cm) long, and fold over a tiny bit at one end. Take the other end and wrap it around the tubing so it covers the slit. Use the folded-over end as a tab that you can pull back to reveal the slit.
Step 3
Take a piece of electrical tape about 2 inches (5 cm) long, and fold over a tiny bit at one end. Take the other end and wrap it around the tubing so it covers the slit. Use the folded-over end as a tab that you can pull back to reveal the slit.
Step 4
Try bending the tubing back so the slit opens up. Then reseal it with the tape. You can test it by inserting the air pump to make sure it is airtight when sealed.
Step 5
Poke one end of the tubing through the gap between the two knots in you tied with the balloon tips.
Add the Balloon Muscle to the Linkage
Step 1
Take a third balloon, inflate it, then let the air out. This is your air muscle. Pull the opening of the air muscle balloon over the end of the tubing that pokes out between the knots. The balloon should cover about 1 inch (2 cm) of the tubing. Secure the balloon to the tubing with a piece of electrical tape.
Step 2
Take the top and the bottom of the balloon diamond and press them towards each other. This is the movement your inflatable hinge will make. Decide how close you would like them to get, and tie the tip of the air muscle balloon to the tips of the other two balloons to hold them in this position.
Step 3
Insert the end of the air pump into the other end of the clear tubing, as far as it will go. Secure it with more electrical tape if needed.
Step 4
Use the pump to slowly and carefully inflate the muscle balloon. As it fills with air, it should lengthen and push the balloon hinge open. To let the hinge close up again, open the release valve by unwinding the tape enough to expose the slit, and bending the tubing back to widen the opening. The air should escape and the balloon return to roughly the same length as when it started.
Troubleshooting: If you’re having trouble inflating the balloon, test out your pump on another balloon fresh out of the package. Cheap pumps break easily. Also check your balloon for leaks.
What Is Happening Here?
About Inflatable Robots
Considering they started as blow-up beach toys, inflatable robots are a lot more useful than you might think! Inflatable robots (and robotic parts) are cheap, lightweight, and collapsible. They’re easy to store and carry around. Plus, inflatable muscles let robots move in a more natural way than gears and motors. No wonder Disney’s animated hit Big Hero 6 featured a friendly inflatable robot named Baymax, a giant blow-up home health aide that fit inside a suitcase when not busy working.
Real inflatable robots come with different types of “skin.” Small and squishy robot grippers and crawlers are made of rubber-y, stretchy material. Larger inflatable robots are often made of stiff material, like a bounce house-style trampoline. Inside, all inflatable robots have one or more chambers that can be filled with air or fluid. To make the robot bend or change shape, pumps move the air around to fill or empty different chambers.
Inflatable robots can be surprisingly strong. The huge walking inflatable Pneubotics created by Saul Griffith’s research and design center Otherlab in California in 2011 looked like very odd horses or elephants and were big enough for several adults to ride on at the same time.
The inflatable robot “elbow” you will be building here was inspired by a type of exoskeleton device called an air muscle. An exoskeleton is like a robot that you wear. It helps you move more easily and can even give you super strength. In the 1950s, a nuclear physicist named Joseph Laws McKibben invented air muscles to help people like his daughter, who lost some of her ability to move when she caught a virus called polio.
Most air muscles use rubber tubing. The version you’ll build is based on a project created by an engineering student named Wyatt Felt. He built a prototype using ordinary twisty balloons — the kind used to make balloon animals. (Felt went on to earn a Ph.D., partner with Pneubotics on another inflatable project, and win several soft robotics awards.) While Felt’s model used a programmable air pump to fill and empty the balloons, you’ll use a regular hand pump and create a valve to let the air out.
The Twisty Balloon Pneumatic Actuator
Explore Wyatt Felt’s original Twisty Balloon Pneumatic Actuator on Instructables. His version uses an Arduino to control an acrylic robot with balloon “muscles.”
What Is Next?
More to Explore
- You can expand on your Robotic Balloon Muscle by making a complete balloon robot body and create your own version of Baymax. Or go abstract and use your muscle to make a mathematical balloon model.
- Balloon twisting can be used for art and engineering! Learn some balloon design tips with these online lessons from Airigami: airigami.com/online-lessons.
- Invent your own inflatable robots using designs from math instead of nature. For example, in 2020 Stanford University researchers demonstrated inflatable tubes that could be bent using motorized corners that slid along their surface. Connecting several tubes into a pyramid created shapes that rolled along under their own power as the lengths of their sides were changed. Find out more at news.stanford. edu/2020/03/18/squishy-shape-changing-bot-roams-untethered.
- Custom-design an edible inflatable robot — see the instructions in my book BOTS! nomadpress.net/nomadpressbooks/ bots-robotics-engineering/.
About the Book
Making Simple Robots, 2nd Edition by Kathy Ceceri is based on the idea that anybody can build a robot! That includes kids, educators, parents, and anyone who didn’t make it to engineering school. If you can cut, fold, and tape a piece of paper to make a tube or a box, you can build a no-tech robotic part.
In fact, many of the models in this book are based upon real-life prototypes — working models created in research labs and companies. What’s more, if you can use the apps on your smartphone, you can quickly learn to tell robots what to do using free, online, beginner-level software like MIT’s Scratch and Microsoft MakeCode.
The projects in this book which teach you about electric circuits by making jumping origami frogs with eyes that light up when you get them ready to hop. You’ll practice designing all-terrain robot wheel-legs with free, online Tinkercad software, and you’ll create files ready for 3D printing. You’ll also learn to sew — and code — a cyborg rag doll with a blinking electronic “eye.”
Each project includes step-by-step directions and clear illustrations and photographs. Along the way, you’ll learn about the real research behind the DIY version, find shortcuts for making projects easier when needed, and get suggestions for adding to the challenge as your skill set grows.
Suggested Add-On: Making Simple Robots Starter Pack
This companion starter pack has all the electronics you’ll need and then some for the projects in Making Simple Robots, 2nd Edition, by Kathy Ceceri (book required for projects).
Materials:
- Twisting Balloons (3). Available in party goods stores.
- Balloon hand pump. An inexpensive one is fine, since you will be building this into the project.
- Clear plastic tubing, 1/4 inch (15 cm) diameter, 10 inches (25 cm) long Available in hardware stores or aquarium shops.
- Tape. Preferably electrical tape.
- Scissors
