Introduction: Making Prosthetic Hands at Home
In my Introduction to Engineering Design class this year, my teacher, Ms. Berbawy, gave us the opportunity to create a project with complete creative freedom. Becuase I wanted to help my community, I decided that the organization E-Nable would be a great way to incorporate engineering with public service. E-Nable is an organization that gives 3D printed prosthetics from the commmunity to those who need tham. They create prosthetics ranging from only a finger to a full arm, with their most popular model being the cyborg beast.
Science has always been one of my many passions. From a young age, I have marvelled at the wonders of assistive technologies and their impact on human lives. When given the opportunity to do the project of my choosing, I took advantage of this opportunity to help other individuals in my community. I have learned a great deal during my time making prosthetic hands, and I know that by making this MakerShare, I can help other individuals do the same.
1- 4 ft Velcro
18 ft Non-flexible string
15 ft elastic cord, 2 mm
5 Aluminum Chicago screws 1/2"
5 Aluminum Chicago screws 1/4"
5 Aluminum Chicago screws 3/4"
5 Aluminum Chicago screws 3/8"
1 Aluminum Chicago screws 3"
5 Tensioner Screw XS
5 Tensioner Screw S
5 Tensioner Screw M
5 Tensioner Screw L
10 Microgel Finger Tips
25" x 6" Adhesive foam squares
1 Roll of Teflon tape
The first step to actually creating this arm is to gain access to a 3D printer. Luckily, I was able to find many in the engineering classroom at my high school. I recommend using an Ultimaker, which has a fine extruder and also automatically takes shells into account to ensure your arm has the proper dimensions.
Then, I found a link, which I have attached below, that has the part files for all of the component files in the hand. Depending on which hand you plan to make (right or left), print the corresponding part files at any scale you desire, however I recommend a scaling of 1.25 or simply 1.00 for the initial print.
Now that all of your parts are printed (may take a couple of days), you may now start assembling the arm. I chose the cyborg beast kit, but any kit you choose will contain all of the materials necessary to actually put the parts together. This makes your life easier because you do not have to buy individual parts.
Then attach each of the fingers to the phalanges by using the chicago screw that best fits the scaling that you have chosen. Attach the thumb and its phalange to the palm as well using this process.
Attach the arm gauntlet to the palm using two chicago screws.
Since the basic structure has now been completed, take the velcro and cut two pieces, one which will go on the underside of the palm and one which will go inside the gauntlet. Create three holes, and fasten these two pieces to the holes in the gauntlet and palm, which have been provided with the print. Now is time to start assembling the tendon lines.
Use this video for easy assembly.
**NOTE** While assembling the tendons, it is important to remember to give yourself enough string to produce tension in the hand. This means that it will be much easier to cut longer pieces of cord, and then shorten those later, instead of finding yourself in a sticky situation when you are unable to tie off the ends.
Cut 5 pieces of elastic cord and 5 pieces of fishing line. Tie a large knot at the very end of each of these strings. Then, begin to string the elastic cord into hole at the center of each finger. Pass the string through the space in the palm, where it will come out of the underside. Then tie a tight knot with the string of the adjacent finger.
Then, do the same process with the fishing line, this time inserting the string into the hole at the tip of the finger, passing it through the palm, and stringing it through the openings at the bottom of the palm.
Lastly, take each string and tie it to a separate tensioner brick. The brick will then be placed into the openings in the arm gauntlet in their corresponding positions in relation to the fingers. You're finished!