Mechatronic Prosthetic With EMG Sensors




Introduction: Mechatronic Prosthetic With EMG Sensors

This project includes four main categories:

1. Composite

2. Armband with EMG Sensors

3. Hardware and Assembly

4. Arduino and Circuits

Together, all of these components show how there can be alterations to commonly done prosthetic pieces. The composite is done in a way that reduces the chance of fracture when added to the other components of the prosthesis. The EMG sensors are made out of conductive thread as opposed to the commonly used sticker electrodes or implanted sensors. In order to have the sensors make a motion occur, hardware, circuit boards, and an arduino code are needed.

Step 1: Composite Supplies

Here is a list of the supplies you will need to complete the composite piece:

-2 Dollar Tree Glass Cylinder Vase 7.5 inch

-Fusion 360 or other 3D CAD tool

-Tape Measure


-ZSK W-head Machine

-Water Soluble backing material

-12K Carbon Fiber

-Nm 40 Thread (color of your choice)

-Bobbin with thread

-Epoxy and Hardener


-Cup to mix epoxy and hardener

-Mixing stick

-Sponge Brush

-Plastic Sheets

-Latex Gloves

-Scrap Fabric

-Metal insert that attaches to motor assembly

-Wax to remove piece from mold



Step 2: Getting Measurements for Fusion 360

To create this composite, we will use a ZSK W-head machine. We will create flat patterns that can later be placed in a mold with epoxy to create a composite. To start, we need to take measurements of the Glass Vase from Dollar Tree that we are using as our mold. We are placing these pieces on the inside of the vase and not the outside.

We need to create 2 pieces. The first one will be a filled circle that is slightly larger than the diameter of the bottom of the vase. The circle will also have a hole designed in the middle that is the same size as the insert piece that will be going through it. This piece will also have 4 arms coming off of it that are 90 degrees away from each other. This will help to hold the structure of the rest of the mold. The second piece needed is a rectangle that covers the surface area of the cylinder part of the mold. This will be the outer part of the composite, holding the circle and arms together.

These pieces can be designed in Fusion 360 or another similar program.

Step 3: Bringing Design Into EPCWin

The design created in Fusion 360 (or other program) can be saved or exported as a .dxf file. This is needed to import it into EPCWin. EPCWin is the program used to create designs and stitch files for the ZSK embroidering machines.

Once in EPCWin, you can import your designs. We will start with the circular piece.

We need a serpent shape to start the design so that the carbon fiber can be caught and in the channel needed to be stitched down. I have it designed to be underneath the stitches that will later be created for the circular piece. I have the serpent shape lead into the inner circle that will be a hole for the insert. I created stitches that followed that path. After that, I created a tight spiral that started where my path from the inner circle ended, and ends on the outer diameter of the larger circle. I also mad this end point be near the start of one of the arms. I then had this spiral filled with stitches.

This circle has only one layer as of right now, but will add a second layer later. It is better to start from the inside and work out for spirals so tension does not create bunching in the center. We will start on the arms next.

Start with making stitches on the first arm that your spiral stitches ended. These stitches should be going in lines extending away from the circle. When these are made into the composite, the lines will need to be going up and down rather than side to side to help the structure. Each arm will have 2 layers made like this before moving on to the next arm.

I created small arcs as drawing lines that are connecting each of the arms. When done with the 2 layers on an arm, stitched can be done on these arcs to get to the next arm. Repeat the 2 layer process on all arms.

Once the last arm is done, we need to create the second layer on the spiral/circle. As mentioned previously, this needs to be done starting from the inside. We are currently on the outside, so we need to make manual stitches or a line with stitches coming from the end point that the start of the spiral in the center. Stitches following this spiral line can then be made.

When done a trim can be added and you're ready to go.

By doing the second layer of the spiral at the end, we avoid the tension issues, and we can sandwich the arm pieces between the two layers of the spiral. This adds some more strength to these weaker areas.

With this method, we have one continuous piece of carbon fiber that can be manipulated into a more customized design, rather than using a sheet of carbon fiber that is normally used. That method involves cutting several individual fibers of carbon fiber and a piece that is not customized to fit the mold. We are trimming only one fiber at the end of the design.

We can bring in the rectangle piece next. This will have a serpent shape on the outside of the top left corner coming in from left to right. The lines for this piece will be vertical for the stability of the piece when becoming a composite. This piece will also have 2 layers.

Step 4: Bringing EPCWin Design to W-head Machine

The next step for the composite is to bring the design from EPCWin to the W-head machine. But first, the machine must be prepped.

Pick a color thread of your choice that will stitch down the carbon fiber. I picked a color that matched other 3D printed parts of my completed design. You will also need a bobbin with thread. I picked black thread for this because it will be easily hidden in the carbon fiber when stitched down.

Next, you will need to frame the backing material that you will be stitching on. I used water soluble backing material. After testing it with our epoxy, it did not have a reaction and could still be washed out after the composite was done if needed. It would also be washed out before creating the composite, but this sometimes leaves the embroidered piece distorted when dried.

Once this is done, the pieces can be loaded onto the machine. Make sure the design fits in the frame based off of your stating position. Once that is done, you are ready to run the designs.

Step 5: Prepping the Mold

Once the pieces are done on the W-head, the can be cut out to be placed in the mold. Save the scrap material for later.

To prep the glass vase that is being used as a mold, the vase needs to be covered in a wax. After a good layer is added to both the inside and the outside of the glass, let it sit to dry for about 5 minutes or so. After the wax feels dry, begin to buff it out. Be sure to buff generously. If there is any wax remaining, it will prevent the epoxy from curing properly.

While waiting for the wax to dry, you can take the second mold and place the embroidered shapes in it. Begin with with the rectangular shape and have it fit around the inside of the mold. Place the circular piece now in the center and push down. If the arm pieces are too long and get in the way. they can be trimmed down to be shorter. Use a paint mixing stick to help push the edges of the circle into place.

Doing this step before adding it to the mold that is waxed will help it hold this wanted shape better without disrupting the waxed surfaces.

Step 6: Prepping the Epoxy

Before adding the epoxy mixture to the carbon fiber and mold, you want everything prepped.

To prevent the epoxy from ruining the surface you will be working on, you want to add a piece of plastic over the work area. You will will want your scale, mixing cup, mixing sticks, sponger brush, latex gloves, additional plastic sheet, scrap fabric, epoxy, and hardener ready to go.

The additional sheet of plastic will be placed inside the mold after epoxy is added. Make sure it is large enough to fit in the mold where epoxy will not come into the inside.

Put on latex gloves. Remove carbon fiber pieces from un-waxed mold and place into waxed mold. Turn on your scale and place the mixing cup on it. Tare the scale with the cup on it. Remove cup from scale and begin to pour epoxy. Read your epoxy before hand to see the ratio of epoxy to hardener needed. The combo I used was 3 parts epoxy and 1 part hardener. For this piece, I used about 3 oz epoxy and 1 oz hardener. I then used a paint mixing stick to mix the combination together. Once thoroughly mixed, I began to use the sponge brush to press the mixture into the carbon fiber. Once all of the carbon fiber looks saturated, pour the rest of the mixture directly into the mold.

Now we will create a vacuum like atmosphere. Take the additional sheet of plastic and place on the inside. Begin placing the scrap fabric inside and pressing down with clean mixing sticks. Watch the sides of the glass and see the epoxy mixture rise. Continue adding and pressing material in until the epoxy reaches the top on all sides and is possibly overflowing.

Leave to cure for at least 24 hours.

Step 7: Removing Composite From Mold

After the Epoxy has cured and the composite is set, we can begin the process of removing it from the mold.

The first step is to remove the scrap fabric that was placed inside the mold. If possible, try to remove the plastic and fabric all at once. It might be easier to remove some of the scrap fabric first and then try the whole package of plastic and fabric.

Once the inside is removed, we can begin to remove the glass. Since there is no air in the bottom of the mold to easily release it, we will have to smash the glass. My suggestion is to place the piece inside of one or two plastic bags and hit the bottom of the glass with a hammer. While in the bags, it will contain glass that will break/shatter. Once the bottom is removed, you can try to slide the piece out of the remaining glass. If that is not working, you will need to just keep hammering away at the remaining glass.

After the piece is removed, you have the option to make it look cleaner if needed. This can be done by a series of sanding the composite and adding another layer of epoxy or clear coat to the outside of the composite piece.

Step 8: Adding Insert to Composite

After the composite is ready to go from the mold, we need to add the insert that will attach it to the rest of the prosthesis.

There is an area of hardened epoxy now sitting in the hole created with the carbon fiber. We will need to drill that out. Once drilled, the piece can be glued in, with the threaded part sticking through the bottom of the composite piece.

An alternative to this that I did not try is to 3D print a piece that will go into the mold before adding the epoxy. This will be placed in the hole in the carbon fiber design, hopefully preventing the epoxy from gathering there.

Once the insert is added, the composite piece is complete!

Step 9: Supplies for Armband With EMG Sensors

-Sewing Machine


-Myoware Board

-Illustrator or similar program

-3D printed case to hold Myoware board


-ZSK F-head machine

-Coated Wires

-Rivets and Rivet Clamp

-Black Spandex Material

-Black Cotton Twill Material

-Water Soluble Backing Material

-Black Paper Backing Material

-Nm 40 Thread (colors of your choice)

-2 Conductive Thread Spools

-Burmilana Thread

-Bobbin with Black Thread

-ZSK K-head Machine

-Velcro Strips

-Electrode Sticker Patches that fit in Myoware board

-Masking Tape

-Double Sided Tape

-3 3-Prong JST connectors

Step 10: Getting Ideas for the Armband

This armband will detect when your muscles spasm due to flexing them. When the sensors pick up these spasms, it will move the motor working as an ankle to move the foot in relation to the composite piece.

We first will look at the Myoware board and see how it works. See what the different parts of the board do, where different sensors should be placed, and what muscle you want to use. The idea is that this could later be a compression sleeve that normally goes under the composite piece on the remaining part of the limb. But for now, it is just an armband to help show this idea. I decided to use the bicep as my muscle of choice. I will have one sensor in the middle of the muscle and one on the bottom closer to the inside joint of the arm. There will also be a grounding patch that will go over the elbow.

Step 11: Designing the Armband

Once you have decided what muscle you want to use, you have to decide where the board will be held and how you want it to be held. From this you can create a 3D printed case that will hold your board on your armband.

With the case design in mind, you can begin to design what the armband will look like. This will be done using the ZSK F-head machine. We will stitch the outline of it on here, along with stitching down certain components. We need to design the piece first and digitize it in EPCWin.

To start, you can use illustrator or a program that is similar to it to create the outline of the armband. What was included in this design was where the 3 sensor patches will go, double lines to see where things will be folded and stitched to make a clean seam, an area that will be cut for the inner part of the elbow so it doesn't bunch up when you bend your arm, an area where the circuit board case will be, and lines indicating where wires will be stitched down.

Step 12: Digitizing the Armband in EPCWin

Once this design is complete in your program of choice, save it as a .AI file so it can be brought into EPCWin. When brought into EPCWin, we can begin to digitize it for the F-head machine.

I used the Comfort Line Program to do the outline of the outside, the outline of the square patches, outline of the board case, and the lines for where the wires will go.

I used a boll stitch program to show where the holes will be lined up for the board case. After these stitches are done, I added a stop into the program so I can manually place the board down when I am stitching it. after that, I have manual stitches to stitch down the board from where the boll stitches are.

After this another stop is added so I can manually place wires on the piece. After this a satin stitch will be done to hold down the wires. This way the wires still can move back and forth slightly but are still secure to the piece.

Once the digitizing is done, we are ready to do a test piece on the F-head.

Step 13: Testing Design on the F-head

It is important to do a test piece first to make sure all of you stops in the design are correct and all of your piece can be stitched down correctly. If changes need to be made to the digitizing, they can be done before you have used your final product material. With this test piece you can ensure the 3D printed part is lined up with the design correctly, and also how long to cut the wires you will be using on the final piece. This also gives good practice for lining up the pieces correctly.

Note that the wires will need to be cut longer so rivets can be added to the ends, and so they have some freedom to move when on an arm.

When you get to the first stop and need to add the 3D printed case, add a strip of double sided tape to the back. This will hold it in place on the material so it can stay still while being stitched down.

When you get to the stop to place the wires down, add a strip of masking tape to both ends of each wire to help hold them in place. Make sure the tape is out of the way of where the stitches will go.

Step 14: Adding Rivets to the Wires

Once you have measure the wire length needed for this piece, you will need to have rivets added to the ends of each of them. One end will be snapping into the Myoware board, and the other end will be snapping into the patches.

You will need the female end of the rivet on the side of the wire connecting to the patches. You will need the male end of the rivet from an electrode sticker patch on the other end of the wire that connects to the Myoware board.

To ensure the male end of the rivet would fit properly in the board, I used electrode sticker patches. I removed the rivet from the foam patch to begin. I then separated the 2 piece of it slightly so I could fit a wire in between them. I then stripped the other end of the wire to have about 1 inch exposed again. I placed this piece between the separated pieces and then clamped them together. I used a pair of pliers to push the pieces back together and clamp them around the wire.

This should be done for all 3 of the wires you will be using.

We will wait to add the rivet to the other end of the wire until the armband is assembled. This way the wire can fit through layers of material without the rivet getting caught.

Step 15: Final Design on the F-head

Now that all measurements have been made and piece have been prepped, the real piece can be made.

Start with putting your black spandex material in the frame with a water soluble backing material. You will want a bright colored thread to see the outline of where you are going to later cut, and a black thread for the other pieces so they can blend in with the armband. The bobbin thread color should be black for this as well.

Begin stitching down your piece. Repeat the same steps when it comes to taping down the board and wires before they are stitched down. When taping down the wires, make sure the correct rivet ends are in the correct directions. The male ends should be at the end of the wire closest to the board case.

Step 16: Cutting and Washing Design

When the design is done on the F-head, you can remove it from the frame. Cut along the outside of the design, following the brightly colored stitching. Now you need to wash out the water soluble backing material. Once rinsed, leave out to dry until completely dried.

Step 17: Created EMG Signal Patches Design

The next step is to create 3 patches in EPCWin that will be made using the ZSK K-head machine. These patches will fit into the outlined piece created on the F-head design.

The 2 patches used to pick up muscle signals are a little smaller than the patch going on the elbow that will be used for grounding. When designing it in EPCWin there should be 2 layers that are perpendicular to each other. The second layer should have a hole left from being stitched in one of the corners. This hole should be the size of the rivet that is going to be snapped into the piece. This should be done for all of the patches. Make sure you also leave enough room between each of the patches so that they can be cut out with a decent amount of the fabric still available so it can be sewn onto the armband.

These patches will be done with a Moos stitch that is made of conductive thread.

Step 18: Using K-head to Create Signal Patches

Now we can bring the design to the K-head machine.

To start, frame the material you will be using. I used black cotton twill and black backing paper that could easily be removed. I used 2 spools of conductive thread and one spool of Burmilana thread. I had all 3 of these coming through the same needle at once.

Once this is ready, you can run the design. It might be a good idea to run it a few times so you have options for patches that you want to use later on for the armband.

Step 19: Attaching Rivets to Patches

After the patches are complete on the K-head, they can be removed and cut out. Now it is time to add the rivets.

The male end of the rivet will be placed on the patches. Start by prepping the rivet clamp with the male pieces. There are 2 sides of your patches. The fluffy side will be in contact with the arm to pick up signals, so we need the rivet to attach to the wire on the other side (the flatter side). Line up the rivet clamp with the circular area on the patch that has less stitches. Clamp down to secure the rivet to the patch.

I suggest testing this rivet a few times with the female end of the rivet to make sure it does not fall out when pulled on.

Step 20: Adding Patches to Armband

Once the patches have rivets added to them and the armband piece is dry, you can begin to add the patches to the armband.

To start, clean up the edges around the outside of the patches. These still need to have enough room to be sewn down, but can be trimmed with clean lines if not done so already.

Then you can line up the patches with the squares outlined on the armband. The fuzzy side will be face up on the back of the armband. Once lined up, pins can be used to hold them in place. You can begin to sew these patches on with a sewing machine. Make sure the wires are clear from the path you are sewing so that they do not get caught in the sewing machine.

Step 21: Finishing Up the Armband

Now we are going to make the edges clean by making good seams.

We will work on the hole for the elbow first. Cut small triangles in the corners so they can be folded over easier. Use pins and pin down the edges to make clean seams. These can then be sewn down with the sewing machine. Pin down the top and bottom edges as well, and sew them down to create a seam.

Use some scrap fabric from the black cotton twill and cut out straps that will be added to the armband. One should be about 1.5 inch x 10.5 inch and the other should be 6.5 inch x 10.5 inch. After these are cut, pin down the edges and sew them to make clean seams.

Cut strips of Velcro (the scratchy side) that will be placed on the shorter ends of each strap. Pin the Velcro down and sew on to the straps.

Lay out the straps on the armband to see where they need to be placed. The larger strap will cover the 2 smaller patches and the smaller strap covers the one larger patch. Pin the larger strap first. It will be pinned backwards to do the stitching. Several lines of stitching should be done to reinforce it. Repeat this for the smaller strap.

Once the straps are added, see where the soft patches of Velcro should be in relation to the strap. Pin these down and sew them on.

Fold the armband in half with the fuzzy patches facing out. Pin the 2 edges together and sew them down. Flip the piece inside out.

Now we need to connect the wires to the patches. Start with stripping the end of the wire so there is about an inch exposed. In the corner where the wire meets the patch, cut a small line in the spandex material. Slide the wire through to where it can connect to the rivet on the patch. Prepare your rivet clamp with the 2 pieces needed for the female end. Place the exposed wire between the two sides of the clamp. Try to clamp some of the coating from the wire as well. Snap the the wire to the patch. Repeat this for all 3 of the wires.

Step 22: Adding Myoware Board to Armband

The armband should be complete at this point.

Now the Myoware board can be prepped to add to the armband. I wanted to use JST connectors to make sure the connection was good, and that if something needed to be replaced it could be done so easily. I soldered a 3 prong connector piece to each of the 3 areas that can have connections made. I did this in case I wanted to try different methods with this piece in the future. I then soldered 3 wires to the connector piece that can clip into the JST pieces I soldered to the board. I added some hot glue to prevent them from touching each other and shorting the system.

Once the board is ready, it can be added to the case attached to the armband. A 3D printed cover for the case can then be added on top.

Step 23: Motor Assembly and Hardware Supplies

-Stepper Motor

-Insert that connects to composite piece

-3D Printed Foot

-3D Printed Piece to connect the motor to the foot

-3D Printed Piece that connects to insert

-3D Printed L-bracket

-3D Printed case to hold circuit boards

-3 4M screws to connect brackets to foot

-1 3M screw to connect L-Bracket to base

-4 4M screws, 8 washers, 4 bolts to connect insert to base piece

-2 4M screws, 4 washers, 2 bolts to connect stepper motor to bracket

Step 24: Assembling Connection With Motor and Composite

The first thing you want to do is to design all the 3D printed pieces and print them out. You will need a bracket that can hold the stepper motor and connect it to the foot, a piece that connects the stepper motor to the inserts, an L bracket to balance the insert, a foot, and a case to hold the circuit boards.

You first want to make sure that your composite piece has the insert added to the hole created at the base. I super glued mine in. Next you want to place your motor in the bracket you created and line it up with the piece connecting the motor to the insert. I made a mark where I the motor would need to be inserted and I drilled a hole. Since the motor is not a regular shape, I drilled a hole large enough for it to fit tightly at its largest areas. Once this is done place the bracket with stepper motor and insert attachment added to it and line it up where you want it on the foot. Place the L bracket on the opposite side from the motor bracket. Mark where you need to drill holes then based on your desired placement. You will also need to drill an additional hole into the piece that connects to the insert where the L bracket will also connect to it.

Once you have marked where everything should be placed, you can drill your holes. After this, gather all of your hardware that will be needed to connect everything. Start with screwing the 2 brackets down to the foot. Then, screw the stepper motor to the bracket. Next attach the insert to its base piece that will attach to the motor and the L bracket. After this, add the base piece to the motor. Since the motor will be lose in some areas, I added some super glue in there to make sure the motor wouldn't slip when it was running. I then added a screw from the L backet into this base piece. Lastly, connect the composite piece to the foot.

Step 25: Arduino and Circuit Board Supplies

The last section of this project is the electrical components. Here are the supplies needed:

-Arduino UNO Board

-Elegoo Stepper Motor Circuit Board


-Coated Jumper Wires (Male on both ends)

-Wires from Myoware Board

-Wires from Stepper Motor

Step 26: Arduino and Circuit Board Assembly

To begin, look up what the different ports on the UNO board are capable of and what you need to run your stepper motor.

To begin, connect the stepper motor wires to the stepper motor board. The wires should have a JST connector that fits into one that is mounted on the board. Next, the stepper motor board needs to have a ground and power jumper wires connecting to the UNO board. I have the power wire plugged into the 3.3V port on the UNO board. Next you need 4 jumper wires to connect the motor board to the UNO board. On the UNO board I have them plugged into ports 7, 9, 10, and 11.

From there, I connected the wires from the Myoware board to the UNO board. The wire connected to "signal" on the Myoware board is connected to A0 on the UNO Board. Ground is connected to ground, and the power is connected to the 5V port. Add circuit boards to 3D printed case created to hold them.

From here, you can work on the code in Arduino to have your motor move when the Myoware board senses a spasm in the muscles from flexing them.

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