Build a Simple Robot with a Tensegrity Structure
30-60 min
Ages 8+
What Will You Make?
Build this surprisingly resilient structure, then make it move.
Tensegrities are known for being squishable and bouncy — but that’s not all they do. The word “tensegrity” — a combination of the words “tension” and “integrity” — was coined by architect Buckminster Fuller, who also invented the geodesic dome. But the structures do more than just bounce. This tensegrity robot is based on prototypes developed by computer scientist John Rieffel and his students at Union College in Schenectady, New York.
Once you’ve built your tensegrity structure, you can quickly put together a circuit to make your robot move using littleBits, electronic modules that snap together magnetically.
What Will You Learn?
You will learn to make careful cuts to construct a tensegrity structure and then use electronics to motorize your creation.
Cut straws
Step 1
Cut 6 pieces of straw to no more than about 5″ long.
Step 2
On each straw, cut a slit on either end, making sure that the slits are aligned (i.e., both vertical). The slits should be ¼” deep — enough to hold the rubber band in place, but not so much that the straw begins to weaken and bend.
Connect straws
Step 3
Line up 2 straws and wrap a small rubber band loosely around each end of the pair.
Step 4
Do the same to a second pair of straws and slide them perpendicularly between the first 2 straws to form an “X” shape.
Add more straws
Step 5
Take the last 2 straws and wrap a small rubber band around one end. Slide them through the intersection of the other straws so that they’re perpendicular to the first 2 pairs, and then wrap a small rubber band around the other end.
Stretch rubber bands
Step 5
Twist one pair of straws so their slits are horizontal and facing you, with one above the other.
Step 6
Stretch a long rubber band from the horizontal slit of the upper straw, up and over a pair of perpendicular straws, and to the other end of the straw, passing it through all 4 slits.
Repeat
Step 7
Repeat Steps 5 and 6 with the all the remaining straws
Step 8
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Cut and adjust
Step 9
Cut away the small rubber bands so that the tensegrity structure springs open.
Step 10
Adjust the pairs of straws so they’re parallel and not touching.
Assemble littleBits
Step 11
Now assemble the littleBits electronic circuit that will make your tensegrity bot go:
Plug the power module (or “Bit”) into the battery.
Attach the dimmer switch module for turning the voltage up or down.
Connect the bar graph module to the dimmer switch. This is a Bit with 5 rows of miniature LEDs; as more power goes through it, more LEDs light up.
Finish
Step 12
Attach one or more wires. The wire modules are short, so use 2 or 3 to make sure your robot has room to move.
Finally, add the vibrating motor. This is a small disc, about the size of a pill, with 2 thin wires attaching it to a magnetic base.
What Is Happening Here?
How It Works
A tensegrity structure can flex, stretch, compress when dropped or pressed, and then spring back into shape. It also has a high degree of compliance, which means it won’t harm people or equipment around it. That, together with its resilience, makes tensegrity a useful framework for robots that need to withstand jolts or squeeze and twist themselves through irregular spaces.
The directions for assembling this six-strut tensegrity structure out of drinking straws and rubber bands are based on a tensegrity icosahedron holiday ornament project from Bre Pettis that appeared on the Make: website in 2007.
Make It Move
The circuit consists of a tiny vibrating motor, a dimmer switch to make it run faster or slower, and a bar graph indicator that shows how much power you’re supplying to the motor. Attaching the motor to the tensegrity structure will make the structure vibrate and move across the table.
To try out your tensegrity robot, attach your electronic circuit to your straw model. Situate the vibrating motor so that none of the electronics get in the way of the tensegrity structure’s motion.
Decide where you’d like to attach the disc end of your motor. Use tape or another adhesive to hold it onto one of the straws. Stretch the motor wire along the straw and attach the motor base and wire base to it.
Turn on the motor and slowly increase the power with the dimmer switch. You’ll start to see the rubber bands vibrate in sympathy, and your tensegrity robot should start to shimmy along the table. See if you can steer it to the right and left by adjusting the power.
If your robot doesn’t move, try attaching the motor higher or lower on the structure. Moving the robot’s center of gravity a little off-center can help overcome its inertia. Now that the robot works, experiment with placing the motor in different locations on the tensegrity structure — in the center, off on one corner — to see which position produces the most reliable and interesting movements. Varying the speed and placement of the motor will produce different kinds of motion, giving the robot a kind of physical intelligence.
Troubleshooting Tips:
If the motor turns on but the tensegrity doesn’t move, flip the tensegrity around so a different side is on the bottom. You can also try moving the motor closer or farther away from the end of the straw.
Find a smooth, flat surface for the tensegrity to glide around.
What Is Next?
Make It Without littleBits
In her book Making Simple Robots, 2nd edition, Kathy Ceceri uses a mini vibrating disk motor, a 3V coin battery, conductive tape, and a binder clip to create the circuit that moves the robot. How can you make the robot move with the materials you have?
Take It Further
While this simple tensegrity robot moves through vibration, advanced tensegrity robots move by contracting their cables and changing shape so they can roll. For an even greater challenge, think about how you could design your robot to do the same. Or break out of the prototyping stage and build a new version of this circuit without using littleBits. Starting here, you’ll be well on your way to making your own advanced tensegrity robots.
Want to make your tensegrity steerable? Add a dimmer switch that lets you make the vibration motor go faster or slower
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:
- Drinking straws (6) (TIP: Keep some spare straws on hand while you’re working. If a straw bends, you’re better off replacing it than trying to fix it.)
- Rubber bands, roughly 5" long (6)
- Rubber bands, shorter than 5" (6)
- Masking tape, glue dots, double-sided mounting tape or other removable adhesive
- littleBits modules: Power, #p1; Dimmer, i6; Bargraph, o9; Wire, w1 (1 or more); and Vibration motor, o4
- Scissors
