Tired of being a human mixer for my sons, so I'm making the Rubik's mixer with my older son. The design I picked for our first step is from Kas' gripper design. It costs about $20~25 to build, but also depends on what you already have. The servo mounts were made for it, however you can use it as you see fit.

https://www.thingiverse.com/thing:2800244

The design is pretty much complete, except the servo mount. In the forum, he provides a servo mount template for the CNC. I don't have access to a CNC machine, so I made this to test out the gripper(90°) and also to mount it as our Rubik's mixer(45°). I actually need 50° for the mixer, because the grippers sag at the end(~5°), plus ~4mm leveling on one side seems making it run better. However that 4mm differences also creates complications during the cube rotation. His forum post also contains the detail instruction/code to make it as a Rubik's solver, see the links below for more details.

https://forum.arduino.cc/index.php?topic=271827.0

The most difficult part of building this is to arrange the final servo mount positions. It took me at least 3 days to get it to a barely working condition. It can run for 5+minutes, but with hiccups occasionally. If it is not aligned in a perfect orientation, then some sort of re-seat operation has to be implemented in the software and that probably slows it down a little. Even though the turning of the cube works ok, I need to re-seat after whole cube rotation. Different plate heights are included and the hot glue/thick paper are good for the final touch. If you can think of a good way to align the grippers, please share/comment your thoughts on this or in the forum.

I use the cheaper Ardunino pro mini (ATmega168, 5V, 16MHz) and the "cloned" Towerpro MG996R ($3+). the combination has a major issue with the varspeedservo library he used. With the Arduino's native servo library, this servo can rotate from 0°~180° without issues. However with the varspeedservo, it tends to spin out of control at the boundaries, like jumping from 160° to over 180° or rotates way lower than 0° to stall the motor when using the function to set with an angle. I have not look into which part is at fault, but I do like the speed control of that library without working on my own. I ended up take an easy route to solve this by modifying the wrist servo(add a 2K resistor to one end of the potential meter, see the picture above). Reading through the code, maybe the attach call to set min/max(544/2400) in cube.cpp should be customized to my servos? Without solving this, you can still use only the 90° rotation in the code to complete all the operations, just slower. If you know what could be wrong in this setup, please also comment and let us know.

https://youtu.be/MMP96zp2YGU