DIY Soft Robotic Tentacle





Introduction: DIY Soft Robotic Tentacle

This instrucable shows you how to make a simple soft robotic tentacle using Ecoflex 00-50 and ballpoint pens.

This project is an easy and affordable way to demonstrate soft robotics. The molds are made from ballpoint pens, only take a few minutes to make and do not require any careful measurements. A single trial size unit of Ecoflex 00-50 contains enough rubber to make over 40 tentacles. This makes it an ideal project for schools or STEM camps that want to introduce students to the field of soft robotics.

Step 1: ​Materials


  • 6 ballpoint pens
  • 6 zip ties
  • Ecoflex 00-50
  • Wire cutters
  • Pliers
  • 1' of 1/8" OD tubing
  • 6' of 1/8" ID, 1/4" OD tubing

Step 2: Making the Molds

Remove the casing from one of the pens and shorten it by about 3/4".

Step 3: Making the End Cap

Take a second pen and remove the head. Continue to remove both the metal tip and the inkwell.

If done carefully, the inkwell can be removed without leaking ink into the head of the pen.

Note: If large quantities of ink leak into the head of the pen, the tentacle assembly can become very messy.

Step 4: Making the Mold

These are the three pieces required to make the mold.

Step 5: Preparing the Mold

Cap the back of the first pen with the empty head of the second. This will center the ink well between the two ends.

To make sure the ink well is centered, roll the pen between your fingers. As the pen rotates, the ink well should not appear to move.

Repeat the process with the remaining four pens. This will make a total of three molds.

Step 6: Mixing the Ecoflex 00-50

Make a 30 gram batch of Ecoflex 00-50 as per Smooth-On package instructions.

Step 7: Filling the Molds

  1. Remove the end cap of the mold.
  2. Fill the mold by injecting the rubber into the pen casing using a plastic syringe.

20 ml of rubber is enough to fill all three molds.

Step 8: Filling the Molds

After the pen casing is full, reassemble the mold, making sure that the inkwell remains centered.

After all of the molds have been filled, place the pens in a cup and wait 3 hours for the rubber to cure.

Step 9: Removing Rubber From the Mold

  1. To remove the rubber, remove both ends of the mold and pull out the inkwell using a pair of pliers.
  2. Slide the rubber off of the ink well.

Empty molds can be reassembled and reused for future projects.

Note: It is common for ink to leak onto the inside of the rubber as it slide off of the ink well. This will not impact the robot's performance.

Step 10: Testing the Actuators

  1. Close off one end of the actuator with a zip tie.
  2. Place an air tube into the open end of the actuator and secure it by hand or with a zip tie.
  3. Inflate the actuator with a plastic syringe. A successful actuator should inflate straight and uniformly.

Step 11: Making the Tentacle

Once all 3 actuators have been tested, assemble the tentacle.

  1. Make about 10 grams of Ecoflex 00-50.
  2. Bond the three actuators together to form a pyramid using additional rubber.
  3. Wait 3 hours for the rubber to cure.

Step 12: Connecting the Tentacle to an Air Source

  1. Cut three pieces of 1/4" OD tubing about 2' in length and three pieces of 1/8" OD tubing 2" in length.
  2. Fit one end of the 1/4" OD tubing onto the tip of a plastic syringe.
  3. Insert a piece of 1/8" OD tubing into the other end of the 1/4" tubing.
  4. Insert the the free end of 1/8" tubing into one of the three actuators.
  5. Do this for each actuator. Once all of the tubing is in place, secure the tubing to the actuator with a zip tie.

Step 13: Inflating the Tentacle

The tentacle is completely soft and can bend in any direction. It is inflated by squeezing the syringes. This particular robot is mainly for educational purposes; however, soft robots like it may one day be used in industry as a delicate grabber or an arm to aid in minimally invasive surgery.

Step 14: Alternative Air Sources

Purchasing bulk quantities of plastic syringes can be expensive. An affordable alternative to the syringe is a simple DIY squeeze bulb.
To make the bulb you will need:

  • A plastic bottle with lid (a least one liter)
  • Nail
  • Hot glue gun
  • 1/8" OD pneumatic tubing (about three feet)
  1. Puncture the lid of the bottle with a nail.
  2. Thread about 0.75" of tubing though the hole in the cap.
  3. Surround the tubing inside the cap (as pictured) with hot glue.
  4. Before the glue cools, screw the cap onto the bottle, block the free end of the tube with your thumb and squeeze the bottle. The pressure inside the bottle will push the hot glue though the any gaps and seal the bottle.

Step 15: Integration of Electrical Components (Project Extension)

    In the future soft robots such as these can be outfitted with cameras to give surgeons a better view of their operation.

    The concept of integrating electrical components can be easily demonstrated using a simple LED.

    During Step 11, insert an LED in the center of the robot's three actuators and wire it to a 5 volt power source.



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    2 Questions

    Each actuatore is connected to a seaparate syringe or bottle.

    The part where you attach the syringe/pipes to actuator is pretty confusing. Are you using one syringe for each actuator or are you somehow connecting the one pipe to all three but is not shown? Otherwise I can assume you are only actively filling one actuator while there is just pipes on the rest which doesn't make sense bcz in the video they all seem to get filled.


    1st thing I thought of when I saw this in an email.

    very nice. I tried one before, from another instructable, which uses ogoo (corn starch + silicone) that worked fine, and I'll try your approach too.
    I'm using an arduino uno to control an air pump to make my "robot" move.

    You have got the gist of it. I applaud your ingenuity, here,s a little secret to take it to the next level,.Buy a long length of coiled spring, open at similar points like your finger ,(these are stretched openings) ,apply pressure inside your tube fitted. Spring will bulge at openings, acting coiled spring duplicates movement like a real finger, Experiment and you could end up with a ROBOTIC HAND.

    Regards Stephen Fitton.

    I can see a hundred uses for this. I make small props for independant movies and this can really be a useful bit of tech I'll add to my skill set. Thanks so much.

    1 reply

    Agreed, might be a good alternative to cable controlled.

    That's really interesting. Cool project!

    That's really interesting. Cool project!

    may be wrong use of word, it must be mechanical or hydraulic tentacle.

    It is widely accepted to describe these soft devices as robotic even if they are manually powered.

    Soft robotics is a sub-field of robotics that deals with Non rigid robots built out of soft and deformable material like silicone, plastic, fabric, rubber, or compliant mechanical parts like springs. Soft robots can actively interact with the environment and can undergo “large” deformations relying on inherent or structural compliance respectively due to the softness or the morphological features of its body.

    Can this be used with liquids to make it stronger? Or will the silicone break or leak with liquid?

    Is it non-toxic? I was wondering if it would be okay to make a giant cool cup with a straw. Thanks in advance!

    1 reply

    The rubber is not advertised as food safe so I would not use it to make a cup.

    The basic concept could potentially be used for a Davy Jones mask? With more advancements to the original project.

    1 reply

    It probably could, however it might be easier to use wire controlled tentacles for that project.