DIY Prosthetic Hand

For this Instructable, we will be building a robotic hand with a variety of cool applications! The design of this hand is focused on cost effectiveness, and accessible materials.

Demo Videos Below:

This Instructable details how to construct a basic animatronic hand controllable by servo. It is part of a larger "DIY Prosthetic" series, however it can also be utilized for other robotic hand related purposes. If you are interested in the potential application as a prosthetic however I detail this more in depth below.

There are a variety of very cool DIY animatronic hands online, however for this project I wanted to build something that actually functioned as a prosthetic, not just a prop. In addition to functionality, I needed it to be able to be replicated, reasonably priced, and basically something anyone could at home.

Of course in order to achieve even the first goal (functionality), I would need to include not only the mechanical aspect that comprised the hand itself, but also a control system that allowed the hand to be used as well, a hand. This presented a bit of a challenge. Modern prosthetic limbs are commonly operated one of three ways, either by using EEG or some other mental connection to allow it to be controlled by thought (too expensive and price-accessible headsets tend to be uncomfortable), by tapping into existing nerves (too dangerous and complicated) or by by utilizing other muscles to trigger the action (I figured if you have to use your natural left hand to operate your right hand prosthetic there is not much of a point).

Eventually I settled upon a design. I figured that the most efficient way to build a truly "DIY" prosthetic hand would be to approach is it less like I am trying to build an extension of the person, and more like I am building a independent robotic system that can operate in conjecture with the person. Therein, the Reaction Prosthetic Hand was born. This prosthetic functions on a reflex basis, acting in response to its environment. it utilizes sensors and Pmods to understand its surroundings, then subsequently the users intention. It then acts upon its intuition.

For this hand specifically, it is a basic clasping motion. It has one degree of motion, and is capable of picking up small lightweight objects. It also is able to perform basic hand-related tasks such as a handshake, wave, shoulder tapping, ect.

The current design uses a chipKIT uC32 and an ultrasonic rangefinder to detect close proximity objects and clasps closed upon anything getting closer than 6 inches.

For this project you will need:

Popsicle sticks

String/thread

Thin coffee straws

Small servo

chipKIT uC32

Construction paper

Duct tape

Hot Glue

Disposable cup

Cardboard

For the physical build of this hand you construct the palm. I did this by making two triangles with Popsicle sticks and hot glue. Then I began to build the fingers (which would eventually be glued between the two triangles. Each finger was build the same, with the only variance being the length. The thumb does not move in my design and is simply a straw with Popsicle sticks hot glued on the sides mounted at a 45 degree angle from the palm.

For each of the other four fingers, take a single Popsicle stick and cut it into thirds. Then duct tape it back together but using the duct tape to create a tiny sliver of space between the joints, to act as a sort of hinge. Then cut the coffee straw into matching length thirds and tape onto the joints ON THE INSIDE of each finger. Run your thread or string through each one and tape at the top of the finger. Then take your rubber band and cut it. Tape to top of finger, then to the back of the palm (make sure its slightly taut) to create tension so the hand stays open.

Finally run the thread between the two triangle palm pieces and out the wrist. To build the wrist I made two small rectangle and then glued the small servo between them so that it could connect to the thread. I used straws as placeholders to support the rest of the rectangle. I then glued the wrist to the bottom of the palm.

Optional: You can either mount the uC32 directly onto the hand to control the servo or you can add a small 3X3 inch cardboard square at the bottom and attach the arm to the Interchangeable Base.

For the physical mounting you can either mount the electronics directly onto the hand or check out my Instructable on how to build a separate mounting platform so you can interchange arms easily!

I used the disposable cup wrapped in cardboard as my mounting system. I then just stick my hand in the cup to move it around. This of course would not be the ideal system if this was being used as a prosthetic however it works decently as a prop or costume!

Note: The Fritzing diagrams are not using a uC32 however they do use the same ports regardless of what microcontroller you elect to use.

Here is the code!

One potential extension of the project would be replacing the rangefinder with Pmod ASL (ambient light sensor) nested in the palm of the hand which is able to sense close proximity objects. It would the be able to operate upon the assumption that if an object is close enough to the hand to trigger the light sensor, the user desires for the hand to grasp the object. So if the light sensor is triggered, it sends a signal to the chipKIT uC32, which then operates a servo that pulls strings connected to the four fingers on the hand. This contracts the fingers and allows it to pick up the object.

In addition, the current system is set up so the hand releases after about 6 seconds, however it would be an interesting extension to utilize the Pmod GYRO to add more control. To release the hand the user has to simply shake it gently, which would triggers the GYRO Pmod. The servo then reverses and releases the object.