Trefoil Tentacle

by gianteye, published

Trefoil Tentacle by gianteye May 21, 2013
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Trefoil Tentacle by gianteye is licensed under the Creative Commons - Attribution license.

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20859Views 2097Downloads Found in Robotics


I've been developing ways to use 3d powder printing to make air powered robots that have no hard moving parts. Using procedural modeling I can create rapid iterations, incremental designs, and inexpensive prototypes with a simple set of tools. Find more details at - http://bit.ly/softrobots

You can see video of this design in action here - https://www.youtube.com/watch?v=EkPeF-sYQ-0

This is an early prototype of a trefoil tentacle. There are three hollow ribbed volumes inside this tentacle that control its motion. It is controlled through a Processing interface and an Arduino switching a bank of solenoid valves using a simple Darlington transistor. You can grab the code here - http://forums.adafruit.com/viewtopic.php?f=25&t=36579 and a detailed tutorial on how to build your own here http://learn.adafruit.com/silicone-robo-tentacle?view=all

This whole project has been made possible by the folks over at http://viridis3d.com especially Jim Bredt. They've been very generous in letting me use their machines and helping me figure out solutions to the material science challenges involved in this kind of work. They're awesome.


Print out three copies of the shell component on a powder printer. This method would also work on a DLP or Objet printer. Print one copy of the block mold. Infiltrate all the parts with an epoxy resin. Wax all the surfaces that will touch silicone to make sure no rubber penetrates into the matrix. If this happens it's guaranteed to lock your mold and you'll have to start again from the beginning.

Pour silicone into the block mold up to its rim. When it's cured, remove it. Use an xacto to split the rubber on the overhang down at one end of the mold. Once you've removed the silicone, flip it over and cast wax into the voids.

Laser cut the alignment jig out of .11" material and assemble it. This will help align and center the wax core. Take all the wax pieces out of your silicone mold and assemble them with the help of the alignment jig. Use a soldering iron to melt the wax between the seams of the tall wax pieces and the base.

Bolt the 3 mold shells together with 1/4"-20 screws and insert the wax core. Pour a slow curing silicone into the holes at the top of the mold. This mold doesn't contain a sprue, so be careful not to pour too quickly and overflow the mold. For a bubble free casting, I recommending putting this whole assembly into a vacuum chamber, but a low viscosity silicone will do a pretty good job all by itself.

When the silicone is cured you can take the mold apart and pull out the wax core. If it doesn't come out cleanly (mine took a lot of fiddling to finally eject) boil the tentacle in soapy water until the wax melts out.

Laser cut the stand out of 1/8" material. Run 3/8" tubing through the trefoil shaped piece, leaving about 1" sticking through it. Stick the tubing into the tentacle, and adhere it to the base using silicone caulk (I use Sil-Poxy). I fastened everything together with luer fittings, and controlled the tentacle using an arduino PWM-ing a few solenoid valves. You can see my code here http://forums.adafruit.com/viewtopic.php?f=25&t=36579

For more details on the process and materials involved, you can look at some photo documentation of a tentacle coming together here - https://secure.flickr.com/photos/gianteye/sets/72157632460625971/ and you can find my complete writeups on the entire soft robotics project here - http://bit.ly/softrobots

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Do you have 3D model for the molded tubes? Instead of casting them i would like to 3D print them

I can't help but think you've created an artificial muscle here! Very cool!

I have seen enough hentia to know where this is going...

Well, it is made of silicone

What if you put another tube up the center and put a lightweight air powered dart gun on the tip? Or maybe a claw grabber?

It seems that the tentacle becomes longer when inflated. Could be an impression or even a desired effect but, I think it could be possible to insert a wire as a central axis, limiting the extension but not the flexibility of the tentacle. the wire would redirect that extension force to flexing more efficiently the limb.

Just a thought, and may be wrong :P

Very nice work!

A great example of taking 3dp a step further!

I've been showing your project to people to demonstrate what can be accomplished by combining FDM with other manufacturing methods.

Thanks so much for the kind words. I'm glad the project is making an impact.

Although I think this project could be done with a well tuned FDM machine, I've never tried it. All of these parts are made with powder printing through repurposed z-corp machines. The advantage is how easy it is to completely seal the molds without having to worry about cracks, and that I can get any geometry out of the machine without having to worry about overhangs or undercuts.

I have some plans on printing some of the core pieces using a soluble FDM material. Keep an eye out for some more experiments pretty soon.

This is great work, excellent job!

WOW! Amazing! Way to think out of the box!

Thank you so much.

Thanks for sharing about this project here -- especially your hard-fought moldmaking/casting techniques!

Thanks. I'm happy to share, especially if people can take what I've built and stretch it into their own creations. I seriously think that soft robotics could take off if there were more people working on getting the techniques for actually making a robot simpler and more well known.