Robotic Hand - Madelyn Agnew

Our project for Computer Technology with Mr. Rilett and Math with Mr. Ciarmoli was to build a robotic hand. This instructable will be a step by step guide on how our group assembled it.

We were required to program a robotic hand to move its pointer finger and thumb in order to create a pinching motion using servo motors.

Although there were many set backs, I feel that after completing this once, I fully understand how to build this hand. It was a very fun project that I would do again.

Below is a list of supplies needed to make a robotic hand.

• Styrofoam
• Servos
• Arduino Nano
• Elastic bands
• Fishing line
• Needle
• Exacto knife
• Sharpie
• Sander
• Needle nose plyers
• Ruler + Scissors
• Paperclips

The first thing that must be done in order to build a robotic hand, is to have parts to assemble it. This involves getting measurements from the model, then tracing and cutting them out on a slab of Styrofoam. For this step, Styrofoam, an Exacto knife, a ruler, and a marker are required.

1. To begin, the model must trace a rectangle around their fingers one at a time on the Styrofoam. The tracings should not be connected.
2. Next, use the Exacto knife to carefully cut out the shapes. There should now be 5 rectangular prisms. It may be good to label them P (Pointer) or M (Middle) so they are easy to differentiate.
3. Then, do the exact same step, but tracing the palm instead. Be sure to cut out a big enough forearm in order to attach the servo motors on later.

Remember to collect measurements of length, width and height for a later step.

The next step that must be done is sanding down the rectangular prisms that were just cut out, into 'fingers'. This step will make them more realistic and mobile. Sanding is only for the fingers, the palm should not be sanded.

Sand down the rectangular prism so that it is round on the sides. When finished, it should look like a cylinder, with a hemisphere on top. Then collect measurements for radius.

When sanding, be sure to not sand too much or too little off.

In order for the fingers to move properly, there must be two 45° angles cut into the finger. A humans finger also has these angles when fully bent.

1. Start by cutting a straight line through the fingers to make it three sections. You should be cutting at where the model's joints are, so they must be used for this step. This should be done by marking off the joints where the models joints are, and cutting from that.
2. Next, take these three sections for each finger and cut a 45° angle. The top with the hemisphere should only have one angle on the bottom, the middle section should have two angles, and the bottom should have one angle at the top.
3. You can gently sand to make smooth, but not take off any access Styrofoam. It may be good to label the fingers again so pieces don't get lost.

Cutting the angles may be done either by eye (using the models fingers) or by using a protractor. Our group did it by eye.

One of the most important steps to do is sewing. This is what makes the fingers able to move. You will need a needle and fishing line for this step.

1. Begin by collecting the pieces that were just cut on angles and put them together for sewing. If the angels were cut correctly, it should look like the finger is slightly bent when they are pushed together.
2. Next, thread the fishing line through the needle and tie a knot on the other side. You are now ready to start sewing.
3. Start sewing your finger by going in from the top and connecting all of the parts. Go out through the bottom and make sure it is able to bend by pulling the string. Repeat until all fingers are sewn.
4. Then, with the excess thread that you have, take your forearm/palm and sew the finger through once. Pull it through and rest it on the forearm. You should be able to estimate where the fingers need to go.
5. After that is done, the excess string must be secured into place. This is done by using paperclips.
6. Cut the paperclips with plyers. You should be able to get three semi-circles out of one paper clip by bending it in a certain way. It is probably good to have around fifteen semi-circles just in case some are lost or broken.
7. Then insert the paperclips into the forearm securing the fishing line down. Two clips per string is a good amount.

Now, when the strings are pulled the fingers will move and look like they are bending.

Fishing line isn't the only thing that will make the fingers bend. Attaching rubber bands will help the fingers to return to their resting position.

1. To start, cut rubber bands approximately so that it will tightly connect the two joints in a finger. There must be two rubber bands per joint, so four rubber bands for each finger except the thumb which only has one joint.
2. Next, hot glue the bands into place.
3. The rubber bands could possibly not be efficient enough to pull the finger back. In this situation, folding up a piece of duct tape and gluing it on the back of the finger might help it.

Building the hand is now complete.

This particular project required two pieces of code. One for math and one for computer technology. The math code required us to find the volume of a hemi-sphere, truncated cylinders and a rectangular prism. This is where all those measurements taken will come in handy.

Python Codes - Math

Python coding involves being particular as the program is very case sensitive. This means that there are a lot of errors dealing with spelling or grammar issues.

The First python code was to find the volume of a rectangular prism subtract the volume of a cylinder. First you must tell the code to find the volume of a rectangular prism. V = length x width x height. Then the same thing for a cylinder, V = math.pi * radius**2 * height. Don't forget to write import math at the start of your code to get the math library.

Finally, tell the code to subtract the two volumes.

The second python code is to find the volume of truncated cylinders. This is to find the volume of a finger that has been cut on a 45° angle. Essentially, it is the same as the first code, but little things like writing volume 1, 2 etc. must be changed along with the equation V1= math.pi * radiust**2 * heightt1 + heightt2.

Arduino Code - Tech.

Coding an Arduino is much simpler. It is also easier to use a program like Tinker-Cad to simulate your code to see if it will work.

1. First, you set up a servo for the thumb and pointer finger. (Servo thumb; Servo pointer;)
2. Then, in void setup, attach the servos to a pin. ( thumb.attach(11); pointer.attach(10); )
3. Next, create void pinch(); and void reset();. These will go under void loop.
4. When telling the code to move the servos, write thumb.write and then however many degrees you want it to move. Reset, will put it back to the way it was, so make sure the degrees will go the opposing way that it first moved.

After code is complete, grab an Arduino Nano and upload the code.

Now that coding is complete, it is time to connect the servos. This is the final step in building a robotic hand. Two servos, and an Arduino are needed.

1. First, the placement of where the servos go must be decided. If a group is only using two servos, there should be lots of space to organize.
2. Second, trace around the spaces where the servos will be.
3. Next, slowly start to cut out the space that is traced out. Do not cut al the way through the Styrofoam. This step is to create a resting spot for your servo.
4. After that, make sure the servo fits with little space to move. It should be in the hand far enough that only the moving part is sticking out.
5. Finally, hot glue the servos into place.

Make sure that your servos are not broken or damaged to prevent having to restart.

Below are some videos of our hand in action.