Animatronic Tentacles With Arduino




***Disclaimer***This instructable is documentation for a work in progress. Although the project is not yet complete, it has reached a place where I believe it can begin to be beneficial to other makers.

The concept for this project was spawned when a friend suggested I be Slenderman for Halloween. When I first looked at pictures, I wasn't terribly excited because I am a prop builder more than a costumer, and Slenderman didn't have any props. However, I then discovered that in some depictions he has tentacle-like appendages emerging from his back. I started scouring the internet, seeing if anyone could give me any advice on how to bring this part of the costume to life. To my dismay, the best I could find was suggestions using armature wire to support the tentacles, but they wouldn't move so I set out to design my own.

The Overall Plan:

-Include 4 or 6 Tentacles

-Be mounted on the back

-Be controlled with 1 or 2 Arduino's using 2 Wii Nunchucks

-Move automatically when not being actively puppeteered

-Have an option to fold tight for moving around tight spaces

UPDATE 2/24/15: Hey Everyone, I am thrilled by the support this project has been getting since I released it just over 2 years ago. I have to say that unfortunately, monetary constraints (being a poor highschool student turning into an even poorer college student) and time constraints have put this project on the back burner for the majority of the last 2 years. I haven't forgotten about you guys, and I am looking forward to delving back into this project soon, hopefully. Don't think I haven't been learning though, in the time away from this project I have picked up numerous skills that I can see applied in hugely useful ways to this project in the future.

These include:

-Learning to machine parts by hand on a vertical mill and metal lathe

-Learned how to use a vacuum form

-Learned a LOT more about servo motors, and what I might need for this project

-Did research on Snake Robots (kind of like tentacles, right?) at the Biorobotics Lab at Carnegie Mellon)

-Learning how to use, and gaining some access to a Waterjet cutter (through Techshop)

-Taking a Class in theatrical casting and mold making at my University

-Beginning to pursue a degree in technical theater

Along with these things, I am also currently taking classes in Welding, Advanced Fabrication Techniques, and Embedded Computing (Arduino-based gadget building) at my University

Thanks for all the continued support, I will do my best to continue to answer any and all questions that come my way in the comments and my inbox. I hope that the next update I post here will be much more timely, and much more full of actual content.



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Step 1: First Draft: Tail - Part 1

In most cases, small scale is usually the way to start a project. For this, however, it was too hard to visualize how everything would work, so I started work on a single, large scale model. Since there would only be one of these, I decided to try to build a tail that had the same functionality that the future tentacles would have. The idea was to use PVC pipe as the "spine" of the tail, and have laser cut 1/8" MDF disc's as the standoff's to make up the vertebrae.

First, I designed the standoff's in Corel Draw. The large hole in the middle was for the PVC and the smaller four holes for the control cables. I then printed these pieces on an Epilog Legend Series laser cutter. It took some experimenting to get the sizing right, and in the process I created an unbelievable number of these discs.

Step 2: First Draft: Tail - Part 2

After I had the right size discs, I cut short lengths of PVC to be connected to them, and hot glued the two together. (Hot glue, like duct tape, is a fantastic tool for quick, dirty fixes, but not for robotics. In the final version, I knew I would have to find something a little more precise.)

Next, I had to figure out how to make the PVC vertebrae slide smoothly against each other. I was unable to find any good system for PVC hinges, so I decided to make a ball joint. I made a sphere of approximately the right size in Solidworks, and then 3D printed them into existence. If I were to do this part over, I would have added a hole down the center of each ball before printing them. As it was, I used a drill press and some scrap wood as a jig to drill a hole in each.

I then connected everything down the middle using tent shock cord to keep the tension, and tied/hot glued it off at each end. After running some spare twine down the sides as the control cables, the first draft was complete.

This first "tail" was far from perfect; it was heavy, and didn't move as it was supposed to.The problem I discovered was that it twisted on itself too much instead of moving directly in the direction it was pulled. This first prototype has been very educational, but it was time to move on to version 2.

Step 3: Tentacle V2

Before moving onto a new prototype, I hit the books to learn as much as I could about animatronics and tentacles. I ended up finding the invaluable resource Stan Winston's School of Character Arts, a large database of videos for purchase, made by the animatronics studio that is responsible for Jurassic Park, Terminator, Alien, Predator, and the Iron Man Suit. This find was a jackpot, they have step by step tutorials for all kinds of mechanisms, including a two and a half hour video on the construction of tentacles of all varieties. I quickly purchased and watched this video, which helped me design version 2.

The Key Changes in Version 2 are:

Speedometer Cable for Spinal Cord - This was suggested in the video referenced above; it can't torque, eliminating the twisting of the first draft.

3D Printed Vertebrae - Though more time consuming than lasercutting, 3D printing would allow me to drill and tap a hole perpendicular to the column, allowing a set screw to hold each piece in place rather than hot glue.

Ability to have Multiple Stages - Will Be Discussed Later

I quickly began by designing the vertebrae in Google Sketchup. I exported these files as .STL's for 3D Printing using this plugin for Sketchup. The first versions center hole diamater had been miscalculated, and the oval-shaped holes weren't evenly spaced. I quickly resolved this with a second version, but soon realized that it would be impractical to 3D print every single one of these, as each took ~7 hours to print. Tentacle version 2 was over before it had even gotten going, and I was back to the drawing board.

Step 4: Tentacle V3 - Step 1 - New Vertebrate

Instead of 3D printing, I redesigned the vertebrae to once again be lasercut. I then had to find a way to hold them tightly to the speedometer cable. I considered using some sort of collar to connect the setscrew to the thin, lasercut material, but couldn't come up with a good way to connect the cut parts to the collar. I finally found small parts called Cord Strain Relief Grips. Intended to hang cords and waterproof cords going into utility boxes, I realized they would be perfect to hold my pieces to the cable. I cut the new pieces in 1/8" acrylic, and tightened the cord grips onto them.

Step 5: Tentacle V3 - Step 2 - Building the Spine

Next, I ran the speedometer cable through the center and tightened the grips down to lock the vertebrae in place. At first, I had them spaced ~two inches apart (the video below shows the tentacle with that spacing). This worked well while hanging, but to be used for Slenderman the tentacle had to be able to support itself while "growing" horizontally out of the back. With the current spacing, it was too flexible to do that. To combat this, I repositioned the vertebrae so there was almost no space between them. They keep moving a little bit because of some room for give right inside the cord grip. This positioning is working much better than the previous design, but I am still playing with it to figure out if it can be made better.

Step 6: Tentacle V3 - Step 3 - the "Tendons"

This time around, I skipped the dinky twine from the "tail" and went straight to thin steel cable. Motorcycle throttle cable to be more precise. To attach the cable to the tip I loosened the cord grip of the last vertebrate and stuck the four "tendon'" cables in with it before retightening. Not only does this hold the cables in place, but it also smooths out the curve at the end of the tentacle that will eventually be covered with the skin. After threading the "tendons" through their corresponding holes, the spine was ready to go.

Step 7: Tentacle V3 - Step 4 - the Skin

For the final version, the tentacle can't look like a jumble of wires and acrylic; to be a "real" animatronic it has to be given a skin. I had to do a lot of research on this, because I had never done anything like it before. I quickly learned that animatronic skins are often either made of foam rubber or silicone. I chose the latter because it seemed easier to work with. When I set out to purchase some, however, I soon discovered that silicone is more of a category than a product. There are many kinds of mixtures that yield different final consistencies for different applications. The product I decided on is Dragon Skin High Performance Silicone from Smooth On. It is advertised as being "used in many special effects applications, especially animatronics where repetitive motion is required." This sounded like what I was looking for, so I ordered the trial (pint) kit size of the medium pot life variety. I made a quick test swatch using a plastic plate as a surface and it came out wonderfully. The Dragon Skin is clear naturally, I colored it with Smooth-On's Silc-Pig dye to create the black color of Slenderman's tentacles.

Next I made a foot long skin to test how the skin and skeleton would fit together. I rotocast this piece using a 2" diameter PVC pipe, capped at the end, as a mold. This made a huge mess, and the skin that resulted was a little thinner than I had hoped. Ultimately, this piece was a learning experience, but the waste of (expensive) silicone that seems inherent in the process, as well as the non-ideal outcome, has led me to reconsider my approach. I am currently looking at new options such as a poured mold.

Step 8: Tentacle V3 - Step 5 - the Brain and Muscles

This part of the build is still very underdeveloped. However I will write briefly about what I have accomplished thus far and where I plan to go.

The brain of the robot is going to be an Arduino Uno. (Though due to the number of motors required to drive all 4 or 6 of the tentacles, I may end up using 2 Arduino's, each running one side.) The Arduino will be used to drive motors (Servo or Stepper) that will pull the cable "tendons" moving the tentacle. The plan is to control this system with a Wii Nunchuck in each hand. The nunchuck is phenomenal because for $11.00 you get an accelerometer, a joystick, and two buttons in a nice, comfortable housing. The plan is to have the joystick control the tentacles when the user wants to puppeteer them, and have the Arduino make them move automatically when he or she doesn't. So far, I have managed to interface the Nunchuck and Arduino to drive one servo in this manner, as you can see below.

The Nunchuck interacts with the Arduino using an I2C serial connection. I don't have enough background in C++ to know how to program this myself, so I consulted many freely available Nunchuck Libraries, some of which are included in the package at the end. The code that deals with getting the Nunchuck input was, therefore, not written by me in any example. My code is the part that processes the values and uses them to move motors.

Step 9: Tentacle V3 - Step 5 - the Back-Pack Mount

This is the only part on which I have done no physical work. The plan is to have a backplate on which the tentacles and electronics will be mounted, and a cover that will protect the electronics and smooth out the back so that it doesn't look too unnatural under clothing. My current plan is to thermoform these out of ABS plastic, but all I have so far is a rough 3D model. (Not to scale)

Step 10: Files and Final Thoughts

This build still has a ways to go before it is complete, and I will keep this post updated as I go. I do have some firm deadlines set currently:

- February 5th - One working tentacle assembly: Spine, Skin, Brain, Motors, and Nunchuck

- April 1st - Full Backpack Assembled and Complete

A Note on Tools: Both the 3D Printer and the Lasercutter are tools I have been utilizing at my High School. I hope to try to save up to get my own in the future. Also, sorry for the not great quality on many pictures, my cell phone camera has been used frequently because I have tended to document hastily in order to maximize time available for making.

Some other small pieces of the design which are not far enough developed to have their own page:
- Belt Pack Control for turning automatic control on and off as well as engaging "close space mode"
- EL Wire through tentacles for light up effects (just for fun)
- Mounting Bracket to make Tentacles easy to remove and service individually

I have uploaded a .zip full of all of the files I have for this project below. Feel free to use it as a resource. Again, the Wii Nunchuck Libraries included are not my own work, but combinations of the work others have shared online. Included are the Vertebrae files, the Arduino Code so far, and the Backpack Model.

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    89 Discussions


    6 years ago on Step 10

    Great project! I would suggest a couple of things, though.

    1. Instead of two Arduinos, consider using just the ATmega chips, as they are far less expensive, and use the same command set (you can buy them with the Arduino boot loader already on them). I use an Arduino to program the ATmega and ATtiny chips, which greatly reduces the cost of projects.

    2. I would try to add more random looking ambient movement to the tentacles. Use a defined range, and slowly transition between two random points within that range for each servo on a tentacle. For fun, randomly choose a delay time, as well, so that some tendons stay in their positions for longer than others. Make sure that this is also constrained to a reasonable range.

    I love the work you've done, and the ideas you've come up with!

    Think of fabrics for the skin. There are many options that are rubbery in appearance, and they'll cost less than silicone. They may weigh less, too.

    4 replies

    Reply 6 years ago on Introduction

    Thanks for the great response jhall30! Now to my replies:
    1. I have looked at this, and for the final version I think I might. I am also working on an Arduino Segway at the moment (Instructable to follow), which might be able to use the same idea. I have seen tutorials on how to program the ATtiny with an Arduino, but not an ATmega. If you have any resources on doing that I would love them, thanks :D

    2. OOOooo. That's cool! I like that better than just sweeping between the extremes! Thanks for the Idea!

    As for the fabric, I've looked at it but my sewing ability is near 0. Though swimsuit type material is starting to sound better after the fiasco of making the test skin. (My dad wasn't too happy with the mess I made in the garage)

    Thanks Again!


    Reply 6 years ago on Step 10

    sorry to ruin any visions of having the first ghetto arduino segway but johndavid400 already made one and its in his book. on the other hand you could just buy his book, follow all or some of the instructions and end with a segway. either way good luck and even if you just follow the instructions, the site could use another organized thoughtful instuctable like this one.

    Hi Awesaomness5,

    I make no claims to my Segway being the first, there are dozens of them on the internet and I have drawn heavily from the information they learned and shared while building their projects.



    Reply 6 years ago on Introduction

    1. You can use an Arduino itself to program your ATmega328p chip, and then pop it out and put in another. It already has the socket for it, unless you're using the SMD version. After all, that's the chip it comes with. If you get them online with the bootloaders already installed, they're plug-and-play in the board. The chips are around $2-3 online through some retailers. It's almost not even worth looking at the ATtiny chips, unless you really want to save space.

    2. Yeah, I've had some luck with that technique in some projects. It keeps things reasonable while appearing random. I usually pick a base, then add a random number to it (which has been mapped to my "reasonable" range). I suppose you could just map the number directly to the range without the addition.

    3. Sewing shouldn't be that difficult. It'll mostly be a straight line up until the end of the tentacle. Just sew it inside-out, and then invert it and slide it on the tentacle. Get a friend to help if you have a sewing whiz around. I'm lazy, of course, so I use a laser to cut fabric.


    6 days ago

    hey liked the slender man want to be a artist make so more art how long has it been senese this person updated do you think he/she has been in a car crash


    Question 6 months ago

    Very nice writeup. Do you know where I can purchase the laser cut vertebrae?



    2 years ago

    heh... I started a similar project a few days ago to make a life size animatronic xenomorph tail. kinda helpful that somebody's already done all the research for me. :-p

    to make my tail, its basically the same mechanism, except I will need to make a cover for it, and that's the difficult part. this cover will need to be reasonably sturdy and will need to be light. I don't suppose you could give me an idea of how heavy that silicone is?


    3 years ago

    If anybody is looking for the "Cord Strain Relief Grips" Adafruit sells them in a couple different sizes but they are called "Cable Gland".

    This is a frackin fantastic project. It looks amazing. I wish I understood more of the robotics part of it as I am trying to do something a bit similar for an Ursula costume. I would love to have tentacles that move on their own..

    You might try neoprene for the skin. its fairly thick, but still is able to stretch and move. Plus, since its used to make wet suits, its obviously durrable.


    5 years ago on Introduction

    Hi. GREAT TUTORIAL! Well explained and interesting subject. I am trying to make a tentacle of sorts but i'm not sure about how you joined the servo motors to the cable. Do you have an photo or graph for that? It would be very helpful if you could publish one. thanks heaps!


    1 reply

    Reply 4 years ago on Introduction

    Hi Danielepoi,

    The reason I didn't post anything about that is because I haven't gotten it to work yet. I don't have a servo strong enough to drive the motor. My plan is to attach the cable to some sort of drum, however. Maybe something like a tiny winch?

    Good Luck!


    5 years ago on Introduction

    Hey i was wondering, would you be able to do what you are doing with the wii nun-chucks with an EEG device? if your not sure well that's ok but if you think it's possible could you message cause i plan on doing this and wearing it at one of my schools carnivals on my last year there, thanks for any info

    1 reply

    Reply 4 years ago on Introduction

    I think it would definitely be possible, though I personally have very little experience with EEG devices. Checkout Backyard Brains and the Myo armband though, they might be able to help.


    6 years ago on Introduction

    Pull some women's panty hose over the device for a skin. Then coat the panty hose with layers of liquid latex. You can also use pieces of tissue paper and unrolled cotton balls with the latex and build up different textures on the device.

    2 replies

    Reply 6 years ago on Introduction

    That is an interesting idea, I have never worked with liquid latex so it would be a learning experience. But, then again, so has this entire project.


    Reply 4 years ago on Introduction

    It's super easy. You can add a touch of acrylic paint to color it and you simply paint it on in thin coats. You end up with a great rubber surface that won't crack. At $55/gallon it isn't as bad as silicone either.


    5 years ago

    Hey just wanted to ask.... How much did this cost? I want to do this for squid girl!