K'NEX Universal Joint (Original & 3D-printed)




Introduction: K'NEX Universal Joint (Original & 3D-printed)

About: Hello! I am mechatronics graduate and have always had a passion for making things. This started at an early age with LEGO and K'NEX. I think it's great to create. From useful stuff to art or toy. The ibles...

Welcome to this ible on how to make a K'NEX Universal Joint. If you don't already know what this is: It's a type of connection between two rotating axles, that may be able to move a certain amound of degrees. I've added a short animation (Credits to Dazz L - youtube) to make the last sentence more understandable.

First I will show how to make a U-joint from original K'NEX pieces. The parts needed for this will be also summed up (not the structure around it) This begins at Step 1.

In the second part of this instructable I will give the .stl-file to the U-joint I designed my own. It was printed for me. It's much smaller, but with the same kind of functionality. The forces (torsion) it can take are probably a bit smaller, but I haven't done any tests. To directly go to this part, move to Step 3.

In the last step (4) I will summarize some pro's and con's about both designs.

See it in work here!

Step 1: Parts Needed

4x 2-way connector Orange/Brown

4x 3-way connector Red/Dark-Gray

1x 8-way connector White/Black

6x Clip with rod end Black

4x Green/Black rod

4x White/Silver rod

2x Rod (may be everything, suitable for your application)

Step 2: Construction

  1. Attach the "Clip with rod end Black" to the end of the longest rod (in your own design, this may be different, of course)
  2. Put an Orange/Brown 2-way connector on the rod end of the clip.
  3. Put another 2-way connector on the other end, and put a White/Silver Rod to attach it.
  4. With a little bit of force, put another White/Silver rod on the other end. (this is not an ideal connection, but it works)
  5. Put two Red/Dark-Gray 3-way Connectors on the white rods and put a "Clip with rod end" on it.
  6. Make this 2 times.
  7. Make a cross with a 7-way (3D-blue) or 8-way and 4 Green/Black rods.
  8. Attach.

Step 3: 3D Printed Piece

Note: The file for the pieces can be found on the end of this Step (as .stl files)

Well, there's not much to say about this. There were some versions of it, 4 to be precise, before I got the actual shape of the hinging part right. It's fragile to put together, but works as it should.

Step 4: Comparison: Original Vs 3D Printed

This was my first 3D printed piece, so it was a new (and enjoyable) experience. I must thank the guy with his 3D printer who let me print the pieces -all the versions- for free. But here goes:

3D printed

+ Much smaller and effective

+ Great flexebility in use (different rod sizes (white rods are possible!))

- Weak. can't handle alot of Torque.

Original K'NEX

+ Original K'nex. Nuff said.

+ Very strong

- Bends some pieces

- Very large and inefffective!

I hope you will enjoy this as much as I did, maybe print a piece (3 actually) for yourself (?) I will try to find a good use and maybe make a short video comparison. But I won't make any promises.
Thanks for reading/watching!



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    35 Discussions

    Oh! one other thing. You said that the 3d printed universal joint can't handle a lot of torque, what gives first? The 3d parts connection or the brown connector? If the brown connector is coming off than just add another brown connector behind and perpendicular from the first. The notch on the one connector behind the front one makes it harder for the brown connector to come off. (learned this from knex gun applications and elastic powered car applications)

    5 replies

    I've added a pic of the final design. If you see those small clips, those will break off first. This has also to do with the way the piece was printed: standing. Why was this done? To get less support material (inside the holes) So... the layers in those clips are in a not so strong position. In all the last designs, one or more of those clips broke off. The original k'nex pieces are injection-moulded.
    And I cannot imagine what you mean by reïnforcing it, I'm afraid. A picture would be more useful.
    For the other comment you made: Shame :/ Altho I understand school. If one would print something, everyone suddenly will :P Nice that you like it ^^


    Maybe you could reprint it on it's side.

    Unfortunately I don't have a 3D printer to use any longer :( I would love to try it though!

    Well I see what will break off now, and unfortunately my reinforcement technique assumes the brown connector is the weakest link so that won't fix it.

    As to reinforcing the part more maybe add some ribs to the outsides of the forks that go from the tips to the base. You'll lose some flexibility in but gain strength. Also you may try bulking up the forks a bit, I know you were aiming at small, but even adding an 1/8th of an inch overall will still produce a smaller component than the knex built version.

    Did you use Autodesk inventor to model this part? If so may I have a copy of the file so I can show you what I'm talking about?

    Yes, my brother also gave me the same hints: reinforce and enlarge/build rough. And yes, It'd still be smaller ^^ The thing is that I didn't want to keep changing so I could finally make this ible ;)
    To answer your question: I used Solidworks, not Inventor :( But after some research I see that you can still open .sldprt files. I'll send a personal message with the file ^^


    1 year ago

    Does the all K'nex U-Joint have a better torque rating than the 3-D printed one?

    1 reply

    Yep, although I don't have any exact data

    I can surely imagine that. The question is why K'NEX didn't come up with more parts (like this for example) themselves?
    And neither do I. Maybe someone you know has one?

    Ya, K'nex needs to make parts like this... Another thing K'nex needs is a bar with teeth on it to make slider things...

    Maybe I should give my CV to them :P so I can introduce new parts

    I don't really know about anyone living close to me that has such a printer. I probably wouldn't use it myself because I like more to use only classic knex parts, and not other materials. It is possible though to make this with knex parts only, so if i ever need it i will use that probably.

    Check 3D Hubs, you can send someone near you the file, and they'll print it and send it to you, or you can come pick it up.

    I wonder if this is possible with just k'nex, I may try to build one as I've found in the past I've needed these!! Great job;)

    4 replies

    Uhm, one is already 100% knex... I don't know if you noticed? :)

    Oh sorry I didn't really see the whole ible! XD

    No worries mate,
    It's easy to oversee things or steps :) Glad you found it ^^
    For what are you going to use it, do you think?