Here we will talk about some decisions to make about how complex your robots grabbing hand or hands will be?
Will it be a simple 2 finger gripper or a one platform magnetic gripper?
Will it be a full five fingers with the movable thumb like a human hand or something less.
Usually as you try to make independently moving fingers you will be adding more servo motors and some type of wires or pulleys or gears.
You can start by studying the internal mechanism of a simple $5 gripper found at many dollar stores or hardware stores.
It will have a trigger at one end which has at least one wire or pole that goes down to the end where it squeezes some simple x shaped plastic and a spring which causes the gripper to open and close like simple fingers on a hand.
You can take that basic mechanism and figure out a way to have multiple fingers being controlled all at once by the trigger at the other end or you can figure out a way to move each finger with a series of wires or poles.
Why not watch this very simple video first before you see a hi-end professional one.
This video is from Youtube user TheJoney which shows how to put together a simple $100 robotic hand that will move at least one finger with an Arduino board. Sure it is pretty simple but it certainly should get a lot of people thinking on how it “can” be done on the cheap. https://www.youtube.com/watch?v=F9R95vmkUso
The Arduino code for the hand is at this weebly site. https://robotguidez.weebly.com/tutorials.html
Now onto the level of semi or full professional robot building.
Will Cogley runs Nilhiem Mechatronics and has a few dozen extremely useful Youtube videos showing how to build movable eyes and robotic hands. In this hand video he describes in great anatomical detail the joints of the hand including the most complex trapezium joint or subtle joint found at the base of the thumb. This joint can rotate in 3 positions and he goes on to describe how to make a robotic type hand to mimic the movement of a real hand. https://www.youtube.com/watch?v=DqGq5mnd_n4
Later you would figure out how to add servo motors to control all of this…or you can simply buy a pre made hand mechanism with a working thumb and add this to the rest of your robot.
The hand and fingers will be attached to a wrist which could be made to rotate and have a servo motor attached.
Then of course the forearm will bend at the elbow where you could add another motor and then at the shoulder.
This is where you start talking about the robots DOF or degrees of freedom and of course the complexity goes up as does the weight and heat created by the arms as they go up and down.
Here is a Youtube video by user Automaton Robotics, showing the possibities of making an artificial muscle controlled arm. https://www.youtube.com/watch?v=gd9d_BAXWvg
Now as of Oct 29, 2021 Automaton Robotics has this even more incredible demonstration of his arm and rapidly moving fingers! I think we have now just crossed over into a new phase of humanoid development! https://www.youtube.com/watch?v=d4lVAMHqHQU
Here is a good example of a 3d printed arm for medical prosthesis use. Its called the Kwawu Arm 2.0 https://www.thingiverse.com/thing:2841281 and the Youtube video demo https://www.youtube.com/watch?v=o5p5qpXizaQ
We could eventually talk about a form of touch sensitivity called haptic and haptic robotics. Check out this company which deals with this technology. https://haptx.com/robotics/