Crude Robotic Hand
I have always been fascinated by the intricate movements of human hands, and in the General Physics II class in 2018 Spring, I uses only simple materials to emulate a right hand.
I would like the robotic hand to be able to curl like we can, and I would also like th movement of each finger to be independent of each other. But before I started my own sketch, I did a little bit research on how human beings are able to move their hands so that my work could emulate how the muscles and tendons work.
Referencing human hands, I came up with the design like the picture on the left, with tendons similar to a real hand. I also considered multiple elastic materials for the tendon: rubber bands, elastic bands,...
Also, I went over several ideas regarding the joint. As shown above, the joint was initially designed to be a thin band of metal, which would raise some questions about durability. The better way would be a joint mechanism.
How to curl the fingers?
After examining how a real hand works, I designed a string-pulling mechanism for the movement of the fingers. The end of the string would be attached to the end of the finger, and when the servo motor is activated, it pulls the string, which pulls the end of the finger in and causes it to curl up.
At that time I did not have access to a 3D printer, and therefore I could not manufacture the exact mechanism designed. Moreover, the elasticity of the tendon behind a finger is also a topic worth exploring.
I tried multiple options, including meltable PLA beads, elastic bands for clothings, ...
I even injured myself during the process, and got a few stitches on my left thumb.
Lucky that I was modeling my right hand!
I designed the fingers to have a string attached to the tip, and each section of the finger would have a hook that fixes the string in place. When the servo motor is activated, the string is pulled such that the tip would be drawn in, pulling the other sections to curl as well.
The rubber band was a decision from trial and error.
This detailed mechanism can be seen in the figures. This mechanism is there to ensure that when the finger turns, the whole finger curls up instead of just moving the final section.