Update (11/22/2013): MUCH cheaper option added to the materials list to replace the squeeze bulbs. Thanks to the education staff at the Franklin Institute in Philadelphia, PA for pointing that out!
Update (4/23/2013): smaller, cheaper "mini" gripper STL file has been added. This gripper will cost less to order from a 3D printing service and won't require as much air to inflate (easier to inflate with a single pump from a squeeze bulb).
Credits: The soft robot technology in this project was originally developed in the Whitesides Group at Harvard University. For more details about the development of the technology and its uses, see the papers Soft Robotics for Chemists and Multi-Gait Soft Robot, and check their publications page for new work. These instructions, which modified the Whitesides Group's original process to be cheaper and more kid-friendly, were developed by a postdoctoral researcher (Dr. Ben Finio) in the Creative Machines Lab at Cornell University (PI: Prof. Hod Lipson), with the assistance of Prof. Robert Shepherd. The work at Cornell was sponsored by the National Science Foundation (DRL-1030865) and the Motorola Foundation. Special thanks to the Ithaca Generator and Ithaca Sciencenter for providing audiences to help us test this project.
"Soft robots" are all the rage in the robotics research community right now. Forget what you usually think about robots and machines - gears, pulleys, circuit boards, aluminum and steel. These robots are made out of soft, stretchable rubbers and plastics, and driven by things ranging from compressed air to chemical reactions and materials that change shape due to electrical current or voltage. Existing robots include a robot worm that can survive being hit with a hammer, a rolling soccer-ball shaped robot, a gripper filled with coffee beans, and even an artificial octopus tentacle.
This project will describe how to make simple, air-powered soft robots that are made from silicone rubber, and shaped using a 3D printed mold. The project is based on a soft robotic gripper and a walking soft robot originally developed by the Whitesides Group at Harvard University:
The project requires access to a 3D printer, or you can order a 3D printed mold from an online printing service like Shapeways, Sculpteo or iMaterialise.
IMPORTANT NOTE ABOUT 3D PRINTER MATERIALS: I can only guarantee that this project should work with an ABS mold. I think PLA should work but have been unable to test that yet. I have also tested both laser-sintered nylon and UV photopolymer molds ("strong & flexible polished" and "detail plastic" respectively on Shapeways), with mixed results. Even with a "polished" finish, the laser sintered nylon has a somewhat porous surface, which can make it very difficult or impossible to remove the silicone rubber from the mold without breaking it. The UV photopolymers can prevent the silicone rubber from curing fully, leaving it with a tacky or even slimy surface. Point being - order these materials at your own risk! A representative from Smooth-On (manufacturer of the Ecoflex silicone rubber) suggested spraying incompatible mold materials with a clear acrylic lacquer, but I haven't been able to try that yet. He specifically recommended Krylon Crystal Clear.
- Ecoflex 00-30 (one "trial kit" is enough to make 5-10 robots depending on size).
- (Optional): Ecoflex 00-50, which is stiffer than Ecoflex 00-30. Using both materials (00-30 for the top layer and 00-50 for the bottom layer) can help the robot bend more easily when inflated, but this isn't required and will drive up the cost of your project. Only recommended if you plan on making a large number of robots (e.g. for an after-school program or summer camp), and need to purchase two or more Ecoflex kits anyway.
- (Optional): Food coloring. The default color of cured Ecoflex is off-white, but you can use food coloring to customize your robots.
- 1/16" ID, 1/8" OD polyethylene tubing* (part number 5181K15 at McMaster-Carr), about one foot per robot
- 1/8" ID, 1/4" OD silicone rubber tubing* (part number 5236K832 at McMaster-Carr), about one inch per robot
- Squeeze bulb: we recommend the "Polaroid Super Blower with Hi Performance Silicon Squeeze Bulb", available at Amazon.com and ritzcamera.com.
- UPDATE: these syringes work just as well and are much cheaper than the squeeze bulbs. If anything, they work better - they don't leak air as much, allowing the gripper to hold its shape better. Much more economical if you are doing this for a large group of students.
- 3D printed mold. The STL file for a basic four-leg gripper is available as an attachment to this page, and is also available on Shapeways and Thingiverse. If you have access to a CAD program (there are some free ones like Google Sketchup and 123D by Autodesk), you can also design your own molds. UPDATE 4/23/2013: I've also added a "mini" gripper STL file - smaller, cheaper to print, and easier to inflate with a single squeeze from a squeeze bulb. This file is also available on this page, Shapeways and Thingiverse. Make sure you read the warning above about materials!
- Plastic cafeteria tray or metal baking tray (metal tray only required if you plan to use an oven, see below)
- Disposable rubber gloves
- Plastic cups
- Coffee stirrers or popsicle sticks
- Paper towels for clean-up
- (Optional) toaster oven. Do not use an oven that you also use for food.
*Note: all of the materials for this project are re-usable except for the silicone rubber. The tubing is very cheap (less than a dollar per foot) so it is not very economical to ship in small quantities - it can't hurt to purchase a few feet of both polyethylene and silicone tubing, in order to make multiple robots.