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). 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.
- 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.
- 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. Important: be sure to order a material with a smooth surface finish (e.g. "White Strong & Flexible Polished" from Shapeways).
- 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.
Step 1: 3D printed mold
If you do not have access to a 3D printer, you can order a mold from an online vendor like Shapeways, Sculpteo or iMaterialise.* Be sure to choose a material with a smooth surface finish - otherwise it will be difficult (or impossible) to remove the cured silicone rubber from your mold. Disclaimer: I tested the directions for this project printing in ABS with an UP 3D printer. I cannot guarantee that other printers or material types will work well with the silicone molding process. It might be a good idea to print a very small test container and do a test cure (follow the steps in the rest of the procedure to mix and cure the silicone rubber), to make sure you'll be able to get your robot out of the mold.
Advanced users: if you have access to CAD software, you can certainly design your own mold instead of using the files supplied here. The paper Soft Robotics for Chemists and its associated supplementary material provide a great introduction to different types and shapes of molds (and the resulting robot motion).
*Note: the 3D printing market is evolving rapidly. This project was originally posted in March 2013, and we can't predict what new 3D printers, companies and services will emerge in the future. You can always do a Google search (for example "3D printing", "3D printing service", etc) to check out what's currently available, and shop around for the best option.