This is a 2 DOF wrist mechanism I designed and fabricated. It was based on the "TeslaBot" wrist, using two parallel linear actuators. The requirements were 3kg load at 200mm from the base (6Nm), yaw +/- 35º, pitch +/- 80º.
The actuators I picked are Hitec Linear Servos 100mm stroke. I chose them because they are lightweight at 54g, and each have 12.4kg of thrust. The compromise is they are rather slow at 7.5mm/sec, however, speed wasn't a constraint for this project.
The screws constraining the front rod-ends are popping out. I hadn't put in locktite yet on this assembly so the spacing nuts were loose.
The trickiest part of this design was finding a rod-end ball joint that could accommodate the near 80 degree required range of travel. I came up with this adapter using parts from the McMaster catalogue and a 3D-printed spacer. By using a low-profile flathead screw and the spacer to constrain the ball, as well as an M5 threaded rod screwed into an 8mm OD standoff instead of an M8 rod, the range of travel was improved enough to meet the specs!
Sadly, I signed an NDA at this point so I cannot show the wrist being controlled. Here is a video of me manually swiveling the joint around: