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The Tentacle

The Tentacle

An articulated tentacle controlled with 3 motors.

I got inspired seeing some snake-like robot, and I was looking for a way to recreate snake-like movements in LEGO. This is the simplest and smallest result I was able to get. The Tentacle consisted of seven identical modules, with three separate strings going through all of them and fixed only to the top one. Each module included a ball joint, which allowed bending in any direction but to a limited angle, unlike the universal joints which would allow bending at right angles, and a wedge belt wheel which simply held the strings. At the same time, the strings were keeping the whole tentacle together and were pulled or released by three independent motors.

It is probably possible to build a much longer tentacle, but it seemed to get harder to control with increasing length. A short tentacle could be controlled manually by simply attaching the strings to some triangular piece mounted on a ball joint, and tilting it by hand. Since there are three motors required, the NXT could be used if somebody is able to create and algorithm that converts movements e.g. of a gamepad stick to the movements of three strings.

It should also be possible to build a much bigger and sturdier tentacle using the ball joints from the 8110 Unimog set, which would also allow to run a driveshaft through the middle, driving some device at tentacle’s top. Running strings through these ball joints could be a little tricky, but I imagine they don’t necessarily need to form a perfect isosceles triangle.


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  1. Aiden
    February 27th, 2015 at 08:09 | #1

    Peter :
    For longer tentacles wouldn’t you just add more strings? If you had six strings, you would probably have much more control as opposed to just three.

    I was thinking that too. I think it might be more difficult to controll, as one motor releasing or pulling a string to move the arm, but more strings would have to work in unison or at least similarly mimicing movement of other strings, but with a workaround they would add more strength and accuracy. But I have basically no idea.

  2. Ev3fan
    February 14th, 2015 at 21:21 | #2

    If I would make this I would use my Ev3 for pulling the strings so I could control it with a gamepad – much more comfortable! 🙂

  3. EV3fan
    November 8th, 2014 at 19:17 | #3

    When I’m building something I’m permanently thinking like “What part will I need next” and “how could I Improve what I have” and searching for parts so that I think it was impossible for me to take pictures of what I’ m building or even posting them on Facebook like you do _ but the reason also could be that I dont really take breaks when building which is why I usually build a model for a maximum of two days.

  4. September 9th, 2013 at 04:14 | #4

    Hi, I made this tentacle with pneumatics.
    It does not move smoothly like yours…

  5. LegoFan101
    September 5th, 2013 at 00:55 | #5

    @Leon Overweel
    Cool… 😮

  6. Sariel
    June 11th, 2013 at 19:48 | #6

    No, it’s not free.

  7. mees
    June 11th, 2013 at 17:23 | #7

    do you know if robotC is free?

  8. Sariel
    June 10th, 2013 at 10:24 | #8

    @Leon Overweel
    Looks really good, I like the smooth articulation between the joints.

    With Photoshop.

  9. June 10th, 2013 at 08:51 | #9

    Hi sariel.
    your Image editing was Awesome, Especially Font, Very many kind of fonts, there are all good! question…. How to make it? I am really wondering…

  10. June 9th, 2013 at 00:24 | #10

    Hey I think we’re on the same wavelength here. I’ve had a prototype a lot like this but a bit bigger together for a couple of months now, but I haven’t had the time to build the supporting structure around it (being a lot heavier mine would probably also be suspended upside down instead of rightside up like yours is.)

    Have you seen Festo’s Bionic Arms at all? That’s where I got the idea for mine; they’re pretty cool too. But yeah I took a quick video of my prototype version, let me know what you think:


  11. Peter
    June 7th, 2013 at 21:35 | #11

    For longer tentacles wouldn’t you just add more strings? If you had six strings, you would probably have much more control as opposed to just three.

  12. Luke
    June 6th, 2013 at 11:26 | #12

    Hahaha, the fencing part made me laugh a lot! Maybe you could make some bigger ones and have a duel with someone else…? 😉

  13. Sariel
    June 5th, 2013 at 22:13 | #13

    I’m not going to do that for a variety of reasons, starting from technical difficulties and ending with the fact that you wouldn’t really see anything interesting. My building processes are shown at Facebook, go check it out.

  14. Harley
    June 5th, 2013 at 21:43 | #14

    Austron, one of the best knex builders, is doing a livestream, through youtube, where he is building his next knex marvel and I thought it would be great if you considered doing something similar. It would give us a great insight into your builds and processes. /watch?v=MjYk0P8iiWU&feature=plcp

  15. Giuseppe
    June 4th, 2013 at 23:32 | #15


  16. gabry
    June 2nd, 2013 at 21:13 | #16


  17. June 2nd, 2013 at 16:44 | #17

    But still really cool! 😀

  18. jimmy3
    June 2nd, 2013 at 16:43 | #18

    Wow, that’s pretty scary! 😛

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