Picture of Twisty Balloon Pneumatic Actuator
My name is Wyatt Felt, I'm a Junior in Mechanical Engineering at BYU.

When I saw the Harvard Soft Robot  wiggling around I was impressed at the simplicity of the actuation. I liked how the legs re-extended with their own elasticity. I wondered whether the idea could be scaled up for skeletal systems. 

I decided to make these uber-cheap, pull-type actuators out of twisty balloons. While there are still some questions of stress relaxation and control, these actuators work at least on a small scale. In theory, they can have a much greater stroke length than either air muscles or pneumatic cylinders. 

It was fun to see the tech teachers at Robogames interested in building them for their classes. If you already have an Arduino and power supply the whole actuator system can be done for under $50.

You'll need                                                                       (what I used)

Arduino or other micro-controller                               Arduino Uno
NPN Transistors (2x per actuator, 1x per pump)    TIP29C (with 1A current limit)
Micro-solenoid valves (two per leg)                           AJK-F0504 though I could've used The Jameco one
Small pump                                                                   AJK-B2703 though Ponoko has one
Leg material                                                                  Flexible plastic (PETG) or an antagonizing spring (another balloon)
Frame                                                                              5.6mm Acrylic though you can use thinner

you can order my frame and legs from

flexible tubing, with barbed tees and connectors                        Home Depot (see pictures)
High current 7v power supply or batteries
Twisty balloons
Zip ties
Small breadboard or Prototyping shield
Soldering Iron
Hot melt glue
Thin gauge wire
Heat shrink or electrical tape

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Step 1: The Concept

Picture of The Concept
The actuator can be modeled as a spring return bellows, pulling when deflated.

iweivoda1 year ago
How did you make sure the balloons would not pop, I'm looking to use balloons and pneumatics on a different project and was intrigued by yours, thanks for any suggestions you can give!
Gene Hacker2 years ago
Where did you obtain the pumps and valves from?
W_world (author)  Gene Hacker2 years ago
This Chinese manufacturer, I don't know how much they like sending out small quantities. About half of what I paid was in shipping.
PS1182 years ago
I think I speak for all of us when I say this: Robotic Wiener Dogs!!! WOOT!!!