How to Make a Robotic Pinching Hand

In this instructable, you will learn how to make a controlled robotic hand. In the final result, the hand will be able to make a pinching motion using the thumb and pointer finger. Keep in mind, this is using cheap and affordable materials so that anyone can make it.

Here is a list of the supplies and materials that will be needed to create the hand:

• Arduino - is used to code the servos so that then can turn a certain degree for the fingers to move.
• Exacto Knife - will cut through the Styrofoam to create pieces of the hand.
• Fishing Wire - this is sewn into the 3 pieces of each finger to hold it together.
• Hot Glue Gun - will be used to glue the rubber bands onto the back of the finger.
• Marker - this is used for tracing the fingers and palm.
• Needle Nose Pliers - this cuts the paper clips into smaller pieces as well as the fishing wire.
• Paper Clips - are cut into small pieces and placed into the palm to hold the fishing wire in place.
• Rubber Bands - these are used to bend the fingers and keep them stable.
• Ruler - a ruler will be needed to get measurements of all you pieces.
• Sand Paper - Is used to sand down the Styrofoam into shapes.
• Servos (2)- this will make the fingers move by connecting the fishing wire to the servos.
• Styrofoam - this will be what the hand is made of.
• USB Cable (USB A to USB B)- used to connect the Arduino to a computer so the code can transfer.

(The image above does not include all of the supplies that will be needed for this project.)

To begin the first step of the project, you will need a piece of Styrofoam, a marker/sharpie, an Exacto knife, sand paper, and a person's hand to model and trace.

• Get a large piece of Styrofoam and your model hand.
• Then, using a marker trace each finger individually as well as the thumb onto the Styrofoam.
• Once all the pieces are traced out separately, you may begin cutting the fingers into rectangular prisms and cut out the palm of the hand.
• Next, when all the fingers are cut out, use a ruler to measure the length, width, and height.
• When all the fingers are measured, you can get sand paper and sand down the rectangular prisms into cylinder-like shapes to make it look like a finger.
• Then, measure the diameter of each cylinder using a ruler.
• Finally, your are going to cut each finger into 3 pieces at a 45 degree angle so that they can bend (the thumb will be cut into 2 pieces instead of 3).

Using Tinkercad, I was successfully able to create a 3D model of how the fingers should be cut into 3 pieces. Use that image as a guide of how to cut the fingers correctly.

This step will include sewing all the pieces of the fingers together and into the palm of the hand. For this step, fishing wire and a sewing needle will be needed.

• To begin, you will need the 3 pieces of Styrofoam that make up the finger.
• Next, you'll need to tie the finishing wire onto the sewing needle. Now, your ready to sew.
• When you begin sewing, you will want to insert the needle at the very bottom middle of your base piece. Then continue threading the needle into the other pieces the same way until you get to the top.
• Once your at the top, make your way down the finger the exact same way. When your sewing, make sure not to sew too tightly or your finger won't bend.
• Then, sew the finger into the top of the palm. When your doing this, bring the needle to the surface of the palm so that you can get all of the fishing wire.
• To end this step, make any extra knots to secure the fishing wire into the Styrofoam and make sure to leave about 20cm of extra fishing wire before you cut it off. Now, repeat this step to all the fingers.

This step is very simple and concludes how to make your fingers secured into place from sewing. To make this step successful, you will need a pair of pliers and paperclips.

• To begin, you will need to get a few paper clips.
• Next, using your pliers, cut the paper clips at the very end making a small arc. Make about 5 for each finger.
• When that is completed, place them onto the Styrofoam arm in a straight line on top of the extra fishing wire from the last step.
• Do that for each strand of wire.

This will insure that the fishing wire holds the fingers and keeps them stable.

The hand itself is almost done!

For this step you will need some rubber bands, duct tape, and something to cut them with, as well as a hot glue gun.

• First, cut a few rubber bands so that each piece is about 3-5cm. You will need two pieces for each joint on each finger.
• Then, you are going to get duct tape, cut it when it's around 5cm and fold it serval times so there isn't any sticky parts. Make 2 of those, one for the thumb and pointer finger.
• When all your pieces have been cut out, you may begin hot gluing them onto the back of the fingers. When doing this, be sure not to glue in between the cuts of each finger or it won't work.

The reasoning for the rubber bands is so that each finger can ben properly without breaking. The duct tape is used so that the finger can return back to the resting position after being bent.

Now, your done the hand itself. Next, we will be working on codes and making the hand move.

In order to get the Servos to move the fingers, we must code them using Arduino. So, for this step you will need 2 Servos, 1 Arduino, and a USB cable to connect the Arduino to a computer.

• First, your going to need the app Arduino downloaded onto your computer.
• Then, create the servos in the code.
• Next, create a loop so that the servo for the thumb can turn 45 degrees and make the pointer finger so that it can turn 90 degrees.
• Now, reset the servos back to the starting positions. This way the fingers can open up again. Make the thumb 70 degrees and the pointer finger 80 degrees.
• Also, make sure to include a delay. For this project, a delay of 5000 was used.
• In order for the code to go from your computer to your Arduino, you must connect it using a USB cable. You also need to make sure to check and see if your code is correct and that it works before attaching the servo to your hand.

That is just an example of how you can code your servos, but it is really up to yourself to create the code.

This next code isn't necessary for the robotic hand to move, but is something extra my group did during the project. There are 2 codes included: how to find the volume of a rectangular-based prism and finding the volume of a truncated cylinder. Also, this math code is done on Python. We used these codes to figure out how much Styrofoam was taken off the rectangular prism when we cut and sanded the fingers.

This is what the measurements are used for from Step 1: Tracing, Cutting, & Measuring.

Now that your servos have code and can move, we just need to attach them to the hand. For this step to work, you will need an Exacto knife, a hot glue gun, and your coded servos.

The first image above is an example of what your hand should look so far.

• First, you will need to cut out a small rectangle on the forearm of the hand. Tracing the Servo onto the Styrofoam using a marker before you cut is a great idea if you want your Servo to fit correctly.
• Then using an Exacto knife, cut out the rectangle and make the cut deep. When doing this, make sure not to cut all the way through the forearm. Leave some Styrofoam at the bottom.
• Keep on cutting the Styrofoam and seeing if the Servo fits tightly. Once it does, you are ready to attach the fishing wire.
• Now, thread the fishing wire through the holes on the Servo. Make sure its not to tight or to loose. Then, when you've found the right length of fishing wire, make a knot and cut the excess wire. Now your ready to glue.
• Simply just hot glue the bottom of the hole you made on the forearm and insert the Servo into the hole.

Repeat this step once more so that you have a Servo attached to the thumb and the pointer finger.

Now your all done and have created a robotic pinching hand!

Here's videos of the final product and getting the fingers to move.

-Deana Draca 2024-06-09