Introduction: Multipurpose Prosthetic


In their daily life, amputees can have trouble performing various tasks that we simply overlook or take for granted. Even with advanced prosthetics, activities such as operating a computer can be difficult. The aim of this project was to stray from the "one size fits all" prosthetic norm. The Multipurpose Prosthetic is a proof of concept design that utilizes interchangeable attachments to perform task-specific jobs. Also, its made with Tinkercad! If you are interested in the native Tinkercad file, send me a note and I will send you the link. This was a project that my partner Sohan and I worked on for the science fair. Neither of us is an amputee so we created a mock prothesis using a water bottle and 3D printing.

How it works

When operating a body-powered prosthetic, the user wears a strap around their opposite arm. A string is connected from that strap to the prosthetic and adjusted to be loose when the user is in a relaxed position. When the user extends their arm, they simultaneously pull on the string creating tension. This tension pulls down on the drill chuck allowing the user to take out or put in a new attachment.

These attachments can be any type of tool with a hex bit attached to them. Ideally, these attachments would be kept or brought into spaces where they are needed. For example, you may carry a pen with you in your pocket but would likely not carry a fork with you everywhere and instead have it near the dining area.


Reiterating on the proof of concept design, this prosthetic has been an ongoing project that first proves that something works and can later be improved upon to be better. I took a shot at making myoelectric attachments that use muscle sensors to activate motors, and am currently working on incorporating computer vision with a partner. The water bottle acts as a mock prosthetic and ideally, you would be able to screw this onto an existing prosthetic when needed.




-Access to a 3D printer

-Glue ex: epoxy

-Tape ex: clear packaging tape



-Filament ex: PLA

-String or some type of wire

- Quick disconnect drill chuck (I used a Dewalt)

- Hex bits

- Water bottle (I used 1.5L)

Make sure the water bottle is large enough for you to fit your arm in. I have relatively small arms so you may need to go up a size. Find a water bottle that fits you. It is preferable that the tube has straight edges or else the workaround may be hard.

Some body-powered prosthetics use a 1/2"-20 threaded attachment. I have included an stl file that could connect the quick-disconnect drill chuck to this type of prosthetic. I used a 1/2"x20x1" hex head screw.

Step 1: Prosthetic Body Prep

Start by determining the section of the water bottle that is going to be used. First, remove the bottle cap and save it for later. Mark a straight line across the near the bottle so that when cut, the bottom of the bottle will be cut off. This whole will act as a place where you can insert your hand into it. Cut along the drawn line with scissors. When finished, cleanly tape the cut edge of the bottle in case of sharp edges. Optionally, you can poke air holes into the bottle for ventilation.

Step 2: Parts in CAD

Download and print the bottle end, drill chuck holder, and ring files attached to this instructable. Note that if you are using a different sized bottle, you will have to modify the dimensions of the files as they are fitted to the materials listed above. For larger bottles, modify the groove dimension of the bottle end piece to match the circumference of your bottle.

Step 3: Assembly

Place the ring on top of the drill chuck and apply pressure so that it slides down onto it. Next, take the drill chuck and use epoxy to secure it onto the drill chuck holder. Use epoxy again to glue your water bottle cap to the drill chuck holder. Once both parts are finished drying, screw the part onto your water bottle.

Slide the bottle end piece onto the cut end of the water bottle. The tape put on previously should help keep it in place.

Step 4: Stringing

Thread your string through the small hole in the ring. Then, tie a knot to secure it in place. Continue to thread the string along the holes on the bottle end piece. After, connect it to your backpack strap and adjust. The string should not feel super tight, but in a position that if you extend your arm, it puts tension and pulls back the drill chuck.

Step 5: Creating Attachments

Here are some of the ways you can create attachments.

1) Creating a temporary tool

If you need a temporary attachment but don't want to damage the tool by drilling a hole and embedding a hex bit into the equipment. You can do this by simply taking a hex bit and taping it onto the tool into a grip position. After you are done using the tool, you can simply take off the tape and hex bit.

2) Creating a permanent tool

If you need a permanent attachment, you can simply drill a hole and implant a hex bit into the hole and secure it with glue. Before doing this, make sure you have the right position marked to drill as that will be your grip position.

3) Creating an adapter

You can create an adapter for a tool as an alternative way to not modify it. This adapter will act as a sort of grip for the tool that can be used for fittings of similar types. For example, if you wanted to create a writing utensil attachment, this method may be preferable as you can swap pencils and pens of similar sizes.

4) Using an existing file

There are many websites like this one that have existing cad files. Using your search bar, you can look for a specific print file like a ping pong paddle. When you find one, simply download it and modify it with a hole to fit your hex bit. After printing, secure the hex bit with glue to create your attachment. Credit to Drewlink555 (ping pong paddle) and Hungerpirat (shovel) on Thingiverse.

5) Creating your own using cad

In the case where something you are looking for has not been made, you can always create your own in cad. Create your desired tool using cad software and modify it with a hole for your hex bit when finished. After printing, secure your hex bit with glue to create your attachment.

Each of the ping pong paddles was created using each of these methods. We also showed other types of attachments that could be created.

Step 6: Switching Attachments

Now you should have at least one attachment to play around with. Your string should be adjusted to the correct length (refer to stringing step). Now, in a relaxed position, you should be able to use your attachment. When you are done with your task, simply extend your arm putting tension on the string, pulling down on the ring, and pulling the drill chuck back allowing you to take the attachment out. This process should be relatively quick and you can put in a new attachment or choose to go without one.

Step 7: Community and School Outreach

We had an opportunity to show our science fair project at the San Jose ComicCon and 3D printed lightsaber adapters for the event.

We also took our project to a local elementary school. Since we knew the kids would be smaller, we modified the design using a smaller water bottle. Of course, the lightsaber adapter was the most popular.

Assistive Tech Contest

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