Week 1

This week, I focused on designing the finger joint. I created a working finger model using cardboard, string, wooden rods, and popsicle sticks.

In the initial stages, I studied hand anatomy, paying close attention to flexor and extensor tendons, ligaments, and joint structures, all to mechanically replicate them. I realized that rubber bands could replicate extensor tendons, while nonelastic string could replicate flexor tendons. The concept was straightforward: pulling the finger with a string would cause it to curl, and releasing the string would let the rubber band pull it back into extension.

A knuckle joint is a connection point that allows two parts to move in a bending motion, similar to how your knuckles work. It’s made up of a pin or rod that fits into holes in both parts, allowing them to rotate around the pin. This movement enables flexibility and bending, just like when you curl your fingers.

The Build

Below are the pieces I crafted: the first piece serves as the fork end of the joint, while the other piece acts as the one-eye end.

The assembly process involved wedging the pieces together, with a rod inserted through them to function as a knuckle pin, thereby allowing rotational movement, as depicted in the illustration.

Following this, I attached another fork end to the one-eye end to replicate the pattern.

 In the end, I had a finger-like structure.

Afterward, I added rods to the back of the finger where I could attach an elastic rubber band.

Additionally, I inserted small rods at the bottom of the finger. This setup allowed the string to catch onto these rods, allowing the gradual pulling of each ligament one by one.

My Issues

I encountered several issues with the first model. Since I had to cut the cardboard pieces by hand and draw them, they weren’t all accurately sized. This sizing issue affected the fitting of each knuckle joint, leading me to cut extra pieces of cardboard. The round areas were jagged and as a result, the finger’s movement wasn’t smooth. This created a lot of friction.

I believe these problems will be solved when I start 3D printing the pieces because the printer can accurately create the right size and curves needed for smooth movement. To make the hand easier to work with, I enlarged the prototype finger design. This won’t be an issue with a 3D printer, as it can produce small parts with accuracy.

Each joint was equally sized, which isn’t true for a normal finger tendon. Additionally, the appearance of the finger isn’t great; there’s uneven hot glue and wear and tear on the cardboard from repeated movement. I plan to address these issues by using plastic for durability.

Despite these challenges, the finger joint designs are a solid foundation, and I’ll continue using knuckle joints for each finger joint.