I'm looking into the topic of ball-joints right now. Including how to design and print them >>8585
. I would also never rule out buying stock parts which are used somewhere, like cars or smaller vehicles. We're her to build robots, not BJ-dolls, but in some places this might be useful, starting with fast prototyping of a skeleton and then having a talking waifu standing around for motivation.
Jumping into the rabitt hole of joints, made me find much more which could be useful, some familiar, but often I also forgot about them.
Regular ball-joints out of steel are used in every automobile, and in many other places, so these might even be available for cheap. Maybe such ones will be useful around the shoulders or the neck, for example. https://en.wikipedia.org/wiki/Ball_joint
- site includes a description of spherical rolling joint from picture one, which looks cool but might not be very useful.
>rod end bearing, aka heim joint (N. America) or rose joint (U.K. and elsewhere): https://en.wikipedia.org/wiki/Rod_end_bearing
>The heim joint's advantage is that the ball insert permits the rod or bolt passing through it to be misaligned to a limited degree (an angle other than 90 degrees)
>If spacing is critical, female heim joints are able to be threaded on, instead of welding inserts to the shaft. When dealing with aluminium shafts, the easiest way to use heim joints is to use the female heim joint.
>Light weight is a key factors when building competitive robots, so using aluminum rods and female heim joints can be key.
>shifter of motorcycles. The shifting mechanism allows forces to be applied linear, but still be able to work at angles when in different gears.
universal joint (universal coupling, U-joint, Cardan joint, Spicer or Hardy Spicer joint, or Hooke's joint): https://en.wikipedia.org/wiki/Universal_joint
>commonly used in shafts that transmit rotary motion.
Then we get to the more human stuff, which was already mentioned here before (pic 5):
> 1: Ball and socket joint; 2: Condyloid joint (Ellipsoid); 3: Saddle joint; 4 Hinge joint; 5: Pivot joint; or in German: 1 Kugelgelenk, 2 Eigelenk, 3 Sattelgelenk, 4 Scharniergelenk, 5 Zapfengelenk
> The ball and socket joint (or spheroid joint) is a type of synovial joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number of axes, which have one common center. This enables the joint to move in many directions.
>An enarthrosis is a special kind of spheroidal joint in which the socket covers the sphere beyond its equator.
and answers, >>7625
How coupling is boing done in other machines should also be a topic of study here, since this might be useful, e.g. making sytems more flexible or safer: https://en.wikipedia.org/wiki/Coupling