Concept; 3-way mobile joint


Firstly, I want to say that I’m not a mechanic engineer, so please excuse the lack of my mechanical/electronic experience.
I’m working on a design competition project which includes the need to move a “blue object” in 3 directions, as seen on image below;

Is there a way to enable such movement in a joint represented with a “red sphere” as on image above!?
If yes, how? I think an existing example with some technical illustrations would help me a lot. I don’t need detailed plans, or electronic shemes, just the mechanical principle.
Any ideas?
Links maybe?

Thanky you,


A three degree of freedom rotational joint with all three axes of rotation crossing at a point is typically called a spherical wrist. They’re common on the end of 6DOF robot arms, and there are LOTS of different ways of actuating them. Unfortunately they’re mostly proprietary designs made by big companies who don’t like putting their schematics online!

By far the easiest way to go is to build three perpendicular rotational joints with very short links between them, which isn’t really spherical at all as the joint axes don’t intersect, but would let you rotate the blue disk in all three axes with a little unwanted translation as well:

You can probably buy hobby servo pan/tilt/roll mechanisms like this, already has pan and tilt modules, and a roll category “Coming Soon”.

To actually have the joints cross at a point you would typically build some sort of gimbal mechanism to keep the parts out of each other’s way, like that space-camp gyro-nauseator ride:

This is how spherical wrists on robot arms usually work.

There are also some really advanced, very compact spherical joints involving bevel gears. Check out this video from the CMU Biorobotics Lab. Each of the two joints of this robot has three rotational degrees of freedom! Keep in mind that this was someone’s PHD project, and probably way more work than you want/need to do for this competition. If you want to see more videos and animations of advanced designs of the compact bevel joints look here.

Beyond that there are some exotic designs involving things like replacing the red ball with a sphere with strong embedded magnets, and suspending and manipulating it with electromagnets, or using three sets of holonomic wheels to support and turn the red sphere:

You generally don’t see these in actual use, like on robot arms in factories, but they are neat!

Good luck in the competition!


nexisnet, aka Adam; I’m impressed. Not only that your fast reply educated and inspired me, but you also have the same name as I do! :smiley:
Not a very common thing. At least not in country I live in.

Well, my first thought was to use something like EDS magnetic levitation, like on modern monorail trains (Transrapid). That is probably something you’ve been thinking of when you mentioned “embedded magnets”. But I don’t have a clue if it is possible to use it in joints. Not to mention; how.

I’m working on a architectural design contest. My project is actually finished, I just wanted to propose a new type of vehicle to match my architectural design. You know; just to back it up there. I don’t need to build it, I just don’t want to put it in my project (3D visuals) if it couldn’t work. Logical theory is probably enough, and this what you provided seems to be more than enough.

Thank you!

aka Adam