Helping Hand
This project is a hand designed to be able to open and close with the press of a button. I decided to create this because I'm fascinated with how the human hand is able to function mostly from tendons that connect the fingers to muscles in the arm.
I was interested in designing movable joints myself, but found a high quality 3D print already created from Team UnLimbited on Thingiverse, which they call the Pheonix Hand.
My part in the project began after assembly of the print, at which point I needed to figure out how to attach the servos to fishing line in order to make the fingers function. In order to do this, I designed a simple laser cut piece of plywood to fit into the hand and hold the servos snugly. Although the design is a bit makeshift, I'm happy with how well it stays in place - no glue required!
The fishing line serves as tendons, running through holes in the print and connecting to each of the fingers. Due to space constraints, I could only fit three servos, so the index and middle finger are controlled by one, the ring and pinky controlled by another, and the thumb controlled by the third.
My other tasks consisted of wiring and coding the Arduino. With a little debouncing and if statements, all went smoothly. I laser cut the wood box to house the Arduino, and had included holes so the buttons could attach flush to the outside. That way, the ugly wiring was (mostly) hidden inside the box.
I originally designed the hand to fully close with one press of the button. However, after testing, I learned that, upon encountering resistance, the servos would cancel their movement and revert to their original position. Essentially, instead of grabbing anything, the hand would just open back up. Instead, I made it so that each button press closes the hand by 20 degrees of the full 180-degree movement of the servos. This way, the user is able to close the hand the desired amount without it re-opening.
Due to the small, cheap servos and the paired-finger setup, there is almost no closing strength. However, once at the desired position, the fingers hold surprisingly well. The biggest issue is that the fishing line tends to slip out of the knots, due to its smooth nature and lack of friction to hold the knots.
