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Air-Powered Soft Robotic Gripper

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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.
 
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Hello!I do this robotic experiments for two times but they all don't work.I used

Ecoflex 00-50 and found that it produces a lot of bubbles when the mixture poured into the mold under 100 °C.Also the tube inserted the robot only two leg can be inflated.How to dissolved this problem?Thank you !

Ben Finio (author)  zaizai2008bj2 days ago

Hi - I'm not sure what you mean by "I used Ecoflex 00-50 and found that it produces a lot of bubbles when the mixture poured into the mold under 100 °C". When you first pour the Ecoflex into the mold, are you waiting for a few minutes at room temperature 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.

If only 2 legs are inflating, you probably used too much Ecoflex in the "glue layer" 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!

Tkank you very much!
Green X6 days ago

cool

dresch1 year ago
Awesome. Take a look at this device that Murata is showing:
http://www.murata.com/products/micromechatronics/feature/microblower/index.html#A002
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.
Great Instructable! THANKS!
Zelenaar dresch1 month ago

dresh,
The microblower looks very promising. Any experience with it ?
Can you easily drive it from an arduino ?
Can you control the flow/pressure ?

dresch Zelenaar1 month ago

Hi Zelenaar,

www.mouser.com sells both the pump and the evaluation kit. Just search "microblower". 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.

https://sites.google.com/site/wayneholder/piezoele...

Ben Finio (author)  dresch1 year ago
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.

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.

*(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)
punypenguin2 months ago

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!!!

Ben Finio (author)  punypenguin2 months ago

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.

Ouranos6 months ago
where do you get ecoflex?
Ben Finio (author)  Ouranos6 months ago
The link is in the materials list above, here it is again in case that isn't working for some reason:

http://www.smooth-on.com/Ecoflex%3D-Superso/c1130/index.html?catdepth=1

Read the materials list for details.
Ouranos Ben Finio6 months ago
thanks and I kind of feel stupid now
Ben Finio (author)  Ouranos6 months ago
It happens :-)
Ouranos Ben Finio6 months ago
oh and can you fix the download buttons because all they do for me is show the codes
Ben Finio (author)  Ouranos6 months ago
I'm not sure what you're asking. Do you mean the download links for the STL files?
The Ideanator9 months ago
Have you tested the system prior to removing the excess silicone, IE could you end up with a tentacle sucker? Also, if you pull a vacuum on this, do the legs go the other way?
Ben Finio (author)  The Ideanator9 months ago
1) Not 100% sure if I understand your first question - you mean prior to using scissors to cut out the perimeter after all the curing is done? No, I haven't tried that - you could certainly give it a shot, but I doubt that you'd get a good seal around the whole edge and get any good suction, with this geometry at least.

2) If you draw vacuum (which I've never actually tried), the legs might bend backwards slightly, but it won't be a perfect mirror image of how they bend forward. It's hard to predict because the Ecoflex's mechanical behavior is so nonlinear. If you want to make a biimorph (leg that bends in both directions symmetrically) it's probably easier to stack two layers on top of each other, which I've done. You can also make connections between layers by printing molds with "snorkels", cylinders that extend vertically upwards out of the mold. Not sure if that makes sense without a picture.
angryrobot1710 months ago
now any 3d printing services???????????????
Ben Finio (author)  angryrobot1710 months ago
I don't understand your question...
jamesb2111 months ago
Hi hahvahdsquah,
I have tried to make this using the exact same materials as you have instructed but am having trouble getting it to fold. instead the mold just wants to expand like a balloon, and one seems to expand more than the other.
I am about to increase the thickness of the side that isn't meant to expand but it is already quite thick. do you have any suggestions?
Ben Finio (author)  jamesb2111 months ago
Hmm. If you don't mind spending an extra $30, you could buy Ecoflex 00-50 (see the updated materials list) and try that for the bottom layer only. I started this project out using only 00-30 (all the procedure pictures and the image on the Introduction were using 00-30) but the 00-50 is a little bit stiffer, so it makes it easier for the robot to curve.

Are you using the big mold or the smaller one I uploaded recently?
jamesb21 jamesb2111 months ago
this is the four legged mould by the way.
ThatCatMan12 months ago
This should have a video of it being used.
Ben Finio (author)  ThatCatMan11 months ago
Here's a video of one I made using food coloring (easier to see on a white background):

http://www.youtube.com/watch?v=g210oczAqGo&feature=youtu.be

The original video from the Whitesides group is probably the best way to see one of these in action (note: I don't recommend trying this with raw eggs at home):

https://www.youtube.com/watch?v=csFR52Z3T0I
Ben Finio (author) 1 year ago
Two updates in case anyone is going to try this out soon:

1) I've included an STL file for a smaller gripper that should be more economical - currently about $20 on Shapeways as opposed to $40 for the larger one; it will also require less silicone to fill the mold, and be easier to inflate with one pump from a squeeze bulb.

2) I've modified the directions for optional use of different materials for the top and bottom layers of the robot (Ecoflex 00-30 and 00-50 respectively). 00-50 is stiffer than 00-30 - this stiffness differential makes it easier for the appendages of the robot to curve when inflated. This can be a nice bonus but isn't required to make the project work.
blorgggg1 year ago
cool project!
Is the silicone rubber tube actually needed? I only saw the polyethylene tubing being used.
Oh, I see now. It is optionally used to connect the polyethylene tubing to the squeeze bottle.
Ben Finio (author)  MrDavidSmith1 year ago
Correct, it depends on what type of squeeze bulb you have. You might be able to get away without it.
annguyen1 year ago
To check for leak, I would use the age old method of checking for bike tire leak. Submerge it into water and pump.

Wonderful instructable, I'm exicted to try it out :D. Maybe make four, or five separate inflatable and make a whole hand out of it.
Ben Finio (author)  annguyen1 year ago
It's actually pretty easy to detect leaks by squeezing the bulb and then listening and feeling for the leak. You can certainly make separate chambers to make different structures (like with the walking robot, linked in the introduction) - we just wanted to keep it simple and cheap for this writeup.
What happens if you draw a vaccuum?
You can 'toughen' it up by adding a mesh fabric into the flat layer (like in composite RTM molding)
Ben Finio (author)  konrad.schellenberg1 year ago
If you draw vacuum I imagine that the channels will just collapse, but the "legs" probably won't bend.

And yes, you can add a relatively non-stretchable mesh fabric to the bottom layer (just soak it in Ecoflex and bond it as a third layer, or include it in the flat layer the first time through). This will affect the curvature of the legs. The cheapest/easiest way to do that is to just use a paper towel soaked in Ecoflex.

If you read the Whitesides papers, they actually used two materials with different stiffnesses (Ecoflex for the top layer with the channels, and I believe Sylgard for the bottom layer), this makes it easier for the legs to curve. We kept it to just one material to keep things cheap and easier for kids - but in order for that to work, the top and bottom layers (amount of material above and bellow the channels) need to be different thicknesses, or else the legs won't curve.
Tomdf1 year ago
Hot dog, I don't think you could have done a better job explaining how to make these! I had no idea the process could be so simple, definitely going on my to-do list.
ehudwill1 year ago
I have to try this sometime.
boeietoch1 year ago
finally i have been waiting for a long time to see this on instructables

good job on the instructable!
Excellent work! Great idea and great instructable too.
rimar20001 year ago
Brilliant debut at Instructables!
randofo1 year ago
Nice! I was doing some 3D printed hydraulic robotic experiments lately and was wondering how you did this. Thank you for sharing your process.
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