Update (1/24/2014): Important note about 3D printer materials added below. Read before you try this project!

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.

Required Materials

  • 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
  • Scissors
  • 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

Download the file 4-leg-gripper.stl or MiniGripper.stl from the links on introduction page (note: the units for the files are in millimeters). If you own or have access to a 3D printer, print your own mold. There are many low-cost "desktop" 3D printers available on the market, such as the Makerbot, Cube, and UP.*

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.
<p>What are your thoughts regarding the using of a liquid as opposed to a gas (hydraulic vs pneumatic)? I am designing a lifelike robotic system (micro-controller actuated) with valves for the release of pressure so that a consistent and constant pressure is maintained throughout the robot and the appendages are only filled (flexed) when the valves close. Do you see any problems with hydraulics in this case as long as the liquid does not dissolve the ecoflex?</p>
Hi - honestly I don't have a good answer. I went with pneumatic largely because that is what the original authors did and I was working in an afterschool setting with kids so it's much less messy if you have holes pop in your robots - no water spilling everywhere. You'd have to dig back into the original research (see links for the Whitesides group) to see if they present a reason for going with pneumatic over hydraulic.
<p>Is this a pneumatic network or a fiber-reinforced actuator?</p><p>Thanks!</p>
Technically it is a pneumatic network, which is a term coined by the original researchers in the Whitesides group at Harvard to describe the air channels inside the robot. This robot does not have any fiber reinforcements, it is just the ecoflex.
<p>Interesting. I asked because the mold seemed slightly different from the pneumatic network and the end result looks quite different (the pneunets have tall channels with thin spaces in between, but this has the channels in a continuous arrangement).</p>
<p>To the best of my knowledge, the definition of &quot;pneumatic network&quot; does not depend on the specific dimensions of the mold. It is a general term used to describe the feature. I intentionally made this mold less complicated than the original Whitesides design so it would be easier for students to modify the CAD files.</p>
<p>I understand Ecoflex is generally used for this sort of gripper/robot. Do you know of any similar materials that would be less compliant? I want to build a gripper that is capable of handling delicate objects and performing manipulation tasks. It seems to me that if I can find such a material, a soft robotic gripper will be optimal.</p><p>Thanks!</p>
<p>Would it be possible to just switch to using 00-50 instead of 00-30 for the entire robot? Would it still be too compliant for manipulation tasks?</p>
<p>Hi - Ecoflex 00-50 should be slightly stiffer than 00-30, and you could build the entire gripper out of one. However, I am not sure how big of a difference in compliance you will see between the two. The company that makes Ecoflex, Smooth-On, has a much larger product line:</p><p><a href="https://www.smooth-on.com/products/">https://www.smooth-on.com/products/</a></p><p>You might want to look into some of their other materials to see what is best for your application. I have called them before and it was very easy to get a sales/tech support person on the phone.</p>
<p>You said the gripper will pop eventually...do you mean if too much air is pumped in or after a certain amount of time? If the latter is true, what is the approximate lifespan of such a gripper?</p><p>Thanks!</p>
Hi - I think the gripper is more likely to pop due to over-inflation than to repeated inflation/deflation at a lower pressure. The material is very stretchy so it isn't like bending a paper clip back and forth where the paper clip will snap eventually. If it does fatigue, you'd measure it in inflation/deflation cycles, not time (since it depends on how frequently you use it), but unfortunately I've never tested that.
<p>Hi,</p><p>I hope you can help me with something as the gluing part is not working for me. <br>I experience that the Ecoflex in some areas around the edges stays &quot;sticky&quot; no matter how long it cures, which is of course creating leaks. I've tried adding more Ecoflex afterwards, but then it will not merge with the &quot;sticky&quot; areas or I can simply peel it off again as a separate layer. I've tried applying a thicker layer in the first gluing step, but then it clogs the air channels (and I get leaks in the edges anyway).<br><br>Do you have any idea why it is not curing properly or have any alternative methods I could try?</p>
Hmmm - unfortunately I've never had this problem before. The only thing I can think of is that you aren't mixing the ecoflex in a 50/50 ratio or you aren't stirring it well enough so it isn't curing properly. I've always found it to be very forgiving of the exact ratio (I always just eyeball it, I don't actually measure 50/50) but stirring it well is important.
<p>Thanks for this. How much can the gripper hold?</p>
I never tested how much it could hold. I'd check the Whitesides group's publications to see if they have those details.
<p>Hi, </p><p>Great work and thank you!</p><p>I have got one question, looking at the 3D printed mould, I think that can only give you half side of the robot? How do you stick the silicones together? I completely understand the process but just can't figure out this particular part of the making. </p><p>Thanks a lot </p>
<p>Did you click through all the steps? The bottom half of the robot is just a flat sheet of silicone made using a tray. It doesn't need a special 3D printed mold. I think looking through all the steps and pictures should answer your questions.</p>
<p>Hi,</p><p>Does it work underwater as well?</p><p>Joey</p>
<p>Hi - sorry I never saw this comment for some reason - as long as the seal is maintained so air doesn't escape, I don't see why it wouldn't work underwater. However, it will probably float when inflated, so you'd have to add weights if you wanted it to sink.</p>
<p>I really dont understand how the seal works here...</p>
<p>Hi,</p><p>I've made this project and it's awesome! I'm looking to make the walking robot. Can I get the STL file somewhere?</p><p>Thanks!</p><p>Sherry-</p>
<p>Hi - unfortunately I don't have the STL file for the walking one. You might be able to create your own using the images in this paper, or try contacting the authors to see if they'll send it to you:</p><p><a href="http://gmwgroup.harvard.edu/pubs/pdf/1135.pdf" rel="nofollow">http://gmwgroup.harvard.edu/pubs/pdf/1135.pdf</a></p><p>There's also a chance it could be available here somewhere:</p><p><a href="http://softroboticstoolkit.com/" rel="nofollow">http://softroboticstoolkit.com/</a></p>
<p>thank you , I'm inspired by you.</p>
<p>Thanks for sharing.</p>
<p>When you grasp an object and try to lift it, the soft robot snaps!! How to overcome this??</p>
<p>Not sure what you mean by &quot;snaps&quot;. Do you mean it pops and the air escapes?</p>
<p>Actually i'd inserted the tube inside the soft robot and when attempted to inflate it, the inserted tube made way for the air to escape sir.</p><p>And one more issue is how much weight can one lift using this??</p>
<p>Generally I've found that if you insert the tube far enough, the silicone rubber will make a seal around the tube. You can try inserting the tube, then adding more silicone rubber around the hole and letting it cure to create a better seal.</p><p>I never tested how much weight they can lift, you might want to check the Whitesides group's publications (see introduction step) for that.</p>
<p>Thank you</p>
This is awesome! It's like a tiny Baymax
<p>Wow! so so so many applications!!!</p>
<p>Note that the tubing can be purchased by the foot at Manhattan Supply Company (<a href="http://www.mscdirect.com" rel="nofollow">www.mscdirect.com</a>). You can enter the McMaster numbers directly in. If you happen to work in a company that will allow you to add this item on to one of their orders, you will cut your cost. Or if you happen to have a distribution center near you, you may be able to walk in and pick up.</p>
<p>I am planning on making one of these</p>
<p>I am planning on making one of these</p>
brilliant. have you seen an organisation called festo? check out www.festo.com/cms/en_corp/13655.htm ?
<p>Yep - I remember their &quot;smartbird&quot; making quite a buzz in the robotics community a few years ago. I didn't realize how many different products they have now.</p>
<p>Thanks for sharing . amazing project.</p>
<p>Hello!I do this robotic experiments for two times but they all don't work.I used </p><p>Ecoflex 00-50 and found that it produces a lot of bubbles when the mixture poured into the mold under 100 &deg;C.Also the tube inserted the robot only two leg can be inflated.How to dissolved this problem?Thank you !</p>
<p>Hi - I'm not sure what you mean by &quot;I used Ecoflex 00-50 and found that it produces a lot of bubbles when the mixture poured into the mold under 100 &deg;C&quot;. When you first pour the Ecoflex into the mold, are you waiting for a few minutes at <strong>room temperature</strong> for all the air bubbles to come out? If you put it in an oven at 100 C right away, the Ecoflex will quickly solidify and trap in the air bubbles. You should wait until there are no more air bubbles before putting it in an oven. You can speed the process along by popping bubbles with a pin or toothpick.</p><p>If only 2 legs are inflating, you probably used too much Ecoflex in the &quot;glue layer&quot; and clogged some of the channels. Try holding the robot up to a bright light, and you should be able to see if the channels are clogged to confirm this. Unfortunately there is no way to fix that and you have to start over with a new robot. Good luck!</p>
Tkank you very much!
Awesome. Take a look at this device that Murata is showing: <br>http://www.murata.com/products/micromechatronics/feature/microblower/index.html#A002 <br>This piezoelectric microblower could make all of these soft robotic ideas easily controllable by standard electronics! I have asked DigiKey if they could carry it. Perhaps if they got several requests we could make it happen. <br>Great Instructable! THANKS!
<p>dresh,<br>The microblower looks very promising. Any experience with it ?<br>Can you easily drive it from an arduino ?<br>Can you control the flow/pressure ?</p>
<p>Hi Zelenaar,</p><p>www.mouser.com sells both the pump and the evaluation kit. Just search &quot;microblower&quot;. Page 16 gives a driver schematic. The microblower needs about 19Vpp at 20mA at 26kHz to run. So no, it can't be driven directly from an Arduino. I think ON/OFF are your only controls, so you can only control flow and pressure by time switching it. Here is someone using one.</p><p><a href="https://sites.google.com/site/wayneholder/piezoelectric-vacuum-pump-for-pick-an-place-machine" rel="nofollow">https://sites.google.com/site/wayneholder/piezoele...</a></p>
You can check out the Whitesides group's papers for info about what they used in terms of air supply and electronics. I think in the first paper they just hooked the grippers up to the lab compressed air supply and manually controlled a valve. In the walking robot paper they used a series of computer-controlled solenoid valves that could pressurize or vent to atmosphere, to inflate and deflate the legs. <br> <br>Point being, we wanted to make this as cheap as possible and accessible to kids, thus the $5 squeeze bulbs*. But absolutely, if you want to do something fancier with offboard or even onboard air supply and electronics, it should be doable. <br> <br>*(which in my experience can provide up to around 5-7psi with a single squeeze if hooked up directly to a pressure gauge- they are limited by their volume though, unlike an air compressor, e.g. if you hook one up to a large chamber with a pressure gauge, the pressure increase will be negligible)
<p>My daughter has been working on this project for a couple of weeks now and we are stumped. We have made 3 4 limbed grippers (we have enough ecoflex for one more) and the same problem happens. The legs inflate unevenly. We worked out all of the other kinks but this one has un stuck. We have added liquid ecoflex to the limbs that are inflating to fast, but if you do that til it works even a little you have to add a thicker bottom to the whole thing or it looses its curl. One of her grippers does sort of inflate, well, almost equally and has a nice curve, but it wont hold anything except the lid to a PAM spray can. I cannot imagine this having the strength to hold even if we do get everything else working. Any suggestions? We are thinking of casting a layer on top of one of those adidas flip flops with spikey soles hoping that will help it hold to lift. We are in the homestretch of this science fair, any help would be very very much appreciated!!!</p>
<p>I replied to your PM - one more thing I forgot - try tying a string around the gripper, like in the video above. That way the air tube is not supporting the weight of the gripper.</p>
where do you get ecoflex?
The link is in the materials list above, here it is again in case that isn't working for some reason:<br> <br> <a href="http://www.smooth-on.com/Ecoflex%3D-Superso/c1130/index.html?catdepth=1" rel="nofollow">http://www.smooth-on.com/Ecoflex%3D-Superso/c1130/index.html?catdepth=1</a><br> <br> Read the materials list for details.
thanks and I kind of feel stupid now

About This Instructable




Bio: For my day job I write K-12 STEM projects for www.sciencebuddies.org. In my spare time I write Instructables.
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