After multiple failed attempts of making other nitinol-based kinetic textile project, I tried making a small shell-shaped wearable brooch using felt and nitinol (shape changing alloy). Below are pictures of the first project I tried before moving on to the shell project.

attempt 1 -pinwheel jacket

The idea was to use the nitinol to pull the fabric from the center of the pattern to expose the color beneath the green fabric. I tested multiple ways of using nitinol. First was to pull in a radiating pattern from the center, as shown in the picture on the left. The nitinol didn’t provide enough tug pull, and also the fabric of the jacket itself (jersey) was too stretchy, and it seemed that the pull action from nitinol was all absorbed by the fabric.

In the next test version, I added stiffness to the jersey fabric at pull-locations by using iron-on paper/cotton fabric. I tried pulling in a triangulated pattern, and also in a radial pattern. Both didn’t seem to work well. The raw edges of the jersey fabric started to curl as well, and it was hard to read the nitinolpull action. I decided to abandon this fabric and use a stiffer fabric for the next test.

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attempt 2 – talking fabric

In the next test, I tried to use nitinol to move the slit as if the fabric was talking (moving its “lips”).  I sewed down the nitiol on the top lip, and zigzaged the nitinol all the way across the slit. That did not seem to pull much. So on the bottom lip, I used nitinol only on the mid portion of the length and did not sewed down the nitinol. It seemed to work better. But I wanted to create more dramatic effect, so I decided to make another one.

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attempt 3 -seashell

In this version, I made multiple cuts and sewed two separated pieces of nitinol. It’s a bit difficult to see in the picture, but there is one nitinol at the top, and another one at the bottom (both are zigzaging). Each nitinol has its own mosfets, and given the thickness of nitinol, I needed to provide 380mA~440mA to activate. Measurement showed 6.9 ohms for the top one, and 7.1 ohms for the bottom one. I added two 1 ohm resisters (mini rectangular shaped resistors) for each of the nitinols to get 9 ohms of resistance on each nitinol.

I made a simple on-off switch with copper tape and sewed it securely to the bottom flap of the shell. After connecting everything I hooked it up to arduino and ran the code. Hmmm.. it didn’t seem to work. The problem seems to be that I used conductive thread to connect to arduino instead of wire. Going back to debug/fix. Meanwhile it worked with the heatgun, but not as dramatic as I hoped it to be. Video is at the top of this post.

The materials I used to make this installation include felt, 2-ply paper, heat-bound paper, about 8 in of flexinol wire, copper tape, fabric glue, conductive fabric, a lilypad arduino, and some wires.

The design of the flower began with a sketch.

The flower comes together in two layers, in alternating petals. There is a pressure sensor inside the step of the flower. When the flower senses someone approaching, it becomes shy and its petals close just a little. To close the petals, I used pre-trained flexinol (or nitinol) wire. I will be using a 3.7volt battery as the power source for this installation. The idea is as the current passes through the flexinol wire, the flexinol contracts due to heat and pulls the flower petals closer together.

The electrical connections is illustrated in this sketch.

The sensor goes to A5 and ground on the Arduino, and each of the petal layers connect via a MOSFET to a digital pin and ground on the Arduino. The other end of the flexinol wire connects to the positive (+) pin on the Arduino. Because flexinol is expensive, I have a limited supply. I decided to make the connections between each individual petal with the help of copper wires. Each individual petal is connected in series with each other on the same petal.

With all that in mind, I began the physical work.

step 1: Cut out the shape of each petal and a circular center piece to hold them together. After assembling the petals onto the center piece, I creased them at the edge of the center piece to aid in folding when they’re pulled by the flexinol.

step 2: I ironed some cloth onto the white paper using the heat-bond paper just to make the flowers look prettier, and I plan to cover the electrical wiring with felt.

step 3: Next, I cut the flexinol into 6 pieces, each about 2 inches. Then I poked two folds into each leave just above the bend crease and put the flexinol through. Because flexinol doesn’t solder, I pinched a crimp bead on each of the ends and saldered the flexinol onto the copper tape. Each piece of flexinol is connected in series with each other.

step 4: After all the soldering is done, I connected a MOSFET to one end of the wire going through the flexinol. The other end of the flexinol wire will be connected to the + on the arduino. Because I don’t want to risk burning the flexinol, I measured the resistance between the two ends. The top petals give a resistance of about 11 ohms and the bottom petals give a resistance of 14 ohms. This means the current passing through the wire using a 3.7 v power source is less than 0.41 mA, the maximum amount of current that can pass through the flexinol with out burning it. For the MOSFET to function correctly, I saldered a 1Mohm resistor in between the legs going to ground and the pin of the MOSFET.

Top petal > resistance: 11ohms ; calculated current: 0.33mA ; measured current: 0.30mA.

Bottom petal > resistance: 14ohms ; calculated current: 0.26mA ; measured current: 0.20mA.

step 5: For the pressure sensor, I made a simple “stem” for the flower using green felt. The sensor is calibrated with a non activated resistance of 11Mohms and an activated resistance of 1kohm.

step 6: Finally, I soldered all the connections to the conductive fabric with which the Arduino pins will be connected. I decided to use wires to connect the petals to the Arduino because the circuit would be too complex (with crossing wires and what not) if I had used copper tape or conductive wire. Pictured below is the side view of the product. The middle of the flower will be used to hold the electrical connections.

The final product of this project does not work as well as I had hoped. The main reason is because I did not have enough flexinol. With the amount of flexinol that I had, I was only able to make the petals move a tiny bit. However, if I had more flexinol to pull each petal, the united force would be stronger, and I would be able to achieve a greater folding action. Another reason is because my cardstock paper is a bit too heavy for the flexinol I have. If I had use just regular paper, the effects would be must more present. Even though, you can see the subtle yet present effect the flexinol has on the flower petals in this video. When the sensor is pressed, the petals fold in ward.

More improvements are being made to the current iteration. I will report back if there are noteworthy changes.

Folding lamp Matrix

I used did a series of tests to determine what the best stitch pattern for a shrinking flexinol wire. These are the diagrams:

Folding lamp Stitch

These are series of tests

The Flexinal had a 6 ohm resistance. I placed 3 1 ohm resisters in series to reduce the current by 9 ohms total in order to not burn out the wire with the 3.7 V battery. The wire only requires 2.2 Volts to recoil.

After completing the circuit and testing all of the traces, I loaded the code. Excited to see it working, I pressed the switch with the USB still attach to the Arduino board pumping 5 volts through the circuit and burning out the wire immediately.

Here is the video as it stands, a vapid flower.

HOT FOLD FAILING

To be continued.

nitinol un-sprung:

nitinol sprung:

diamond pleat folded structure:

nitinol spring inside:

after applying heat:

wiring to lilypad:

mosfet setup:

switch:

setup in progress:

So far it works with a heat gun….

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Flexinol wire can exhibit an astonishing grace when it lifts up with current and then relaxes without. I find this movement particularly elegant when the piece of fabric (with flexinol stitched in) is suspended. Then, the action of lifting up with current then slowly releasing without is most balletic.

I had initially imagined creating a series of hung pieces that, when activated, would nest one into another … much like the petals of a flower. However, the behavior of the longest length of wire (about 6.5″) was not as I expected. Rather than simply curling in a single arc, it curled round several times, much like a ringlet of hair. Quickly making adjustments, I then decided to aim for a simple see-sawing motion with two pieces that, in syncopated rhythm, would curl in this ringlet formation.

This short video demonstrates this:

http://vimeo.com/38043849

The calculated resistances are as follows:
For switchPin1, the resistance in the wire itself measured 13.8 ohms. Adding to that the resistances in all the other strands of connecting wire, I got a total of 14.5 ohms. As I chose to use my computer to power the arduino, I calculated the current by dividing 5volts (the voltage coming out of my computer) by 14.5 ohms.

V = I * R

5 v =  I * 14.5ohms

I = 0.34 amps (just shy of the targeted range of 0.35 – 0.41 amps required to trigger the 0.006″ diameter nitinol wire to move)

For switchPin2, the resistance in the wire measured 10.3 ohms. As I would need a bit more resistance to lower the amount of current in the circuit, I added two 1 ohm resistors to the circuit. In total, I had 12.6 ohms. Therefore:

5 v = I * 12.6 ohms

I = 0.40 amps (perfectly on target!)

I placed the piece on a simple structure that elevates it off the ground such that the wire strips hang. When I first tested it, switchPin 2, or the left arm, activated while switchPin 1 did not. After checking all the connections for the unresponsive switch, I discovered a blocked connection. After fixing that, I tested the piece again and this time switchPin1 did indeed transform but then switchPin 2 seemed to have gone lame! I wonder if there is something incorrect about my wiring such that the current is directing itself via the shorted possible route. Just a guess … will have to test further to figure this out.

http://vimeo.com/38043960

1. Cut out the bunny shaped template pictured below. You can download the pdf version at the bottom of this post.

2. Use conductive tape, flexinol, mosfet to outline the circuitry depicted below. Use threat to secure the flexible around the ears area. Also put snaps on the paper to make space for the lilypad.

Note: make sure the flexinol is sown snugly on the ears

Note: make sure all the connection point on of the copper tape are secure, use a multimeter tocheck conductivity.

Note: this is how the front of the bunny looks. make sure all connection points are secure.

3. Program the arduino board and snap on the bunny, assemble the bunny in shape

Bunny Ear in action

https://vimeo.com/40136179

Calculation

I=V/R

I=0.41A

V = 3.7V

R predicted =appx 9 Ohms

R of circuit = 3.7 Ohms

I need 5 Ohms more -> add 5 more 1 Ohm resistors.

This week I decided to actuate three strips of felt with the nitinol. My goal was to understand the material, and the electronics… the circuitry behind the whole thing. Since i would be activating three strips separately, I would need three mosfets.

A MOSFET is a voltage controllable switch, “a metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) used for amplifying or switching electronic signals.”

I stitched and soldered the components that I would need to create my circuit for our assignment. Above you can see my mosfets with their respective 1M Ohm resistors. The nitinol must be prepared to be soldered to the conductive fabric. The ends of the nitinol was curled into a hook and inserted into a crimp bead. Then using a pliers the nitinol was squeezed tightly in the crimp bead. I stitched the nitinol down to the felt with a zig-zag stitch then soldered the ends to the conductive fabric.

Photo showing all three nitinol strips, mosfets, and location of Arduino on the left

After stitching and soldering my main components, I troubleshooted my circuit. Above is a sketch of the connections I made to test. IT WORKED!!!

After checking the resistance of each nitinol strip – based on Leah’s advice – I realized that I was short of resistance and could run the risk of damaging my wire, and draining my battery. Using my multimeter I calculated the following:

Calculations

V = IR

Voltage = 3.7V (battery)

I = 400 mA (max. current for the .006″ wire)

R = 3.7V/ 0.4 A

R = 9.25 Ohms

I had to add resistance to each circuit.

Above is a photo of what I did to add resistance. I decided to use 1 Ohm resistors that are soldered onto PCB Boards as this was a neater option. I added 3 or 5 together as needed and soldered to my circuit as shown below.

3 Ohms were needed here, but I added a 0 Ohm resistor to increase the length of the bridge.

Resistance of 5 Ohms added

Arduino Code

int internalLED = 13;
int Nitinol1 = 5;
int Nitinol2 = 6;
int Nitinol3 = 9;

void setup() {                
 // initialize the digital pin as an output.
 // Pin 13 has an LED connected on most Arduino boards:
 pinMode(internalLED, OUTPUT);
 pinMode(Nitinol1, OUTPUT);
 pinMode(Nitinol2, OUTPUT);
 pinMode(Nitinol3, OUTPUT);
}

void loop() {
 digitalWrite(13, HIGH);   // set the LED on
 delay(1000);              // wait for a second
 digitalWrite(13, LOW);    // set the LED off
 delay(1000);              // wait for a second
 digitalWrite(Nitinol1, HIGH);   // set the first leg on
 delay(1000);              // wait for a second
 digitalWrite(Nitinol1, LOW);    // set the first leg off
 delay(1000);              // wait for a second
 digitalWrite(Nitinol2, HIGH);   // set the first leg on
 delay(1000);              // wait for a second
 digitalWrite(Nitinol2, LOW);    // set the first leg off
 delay(1000);              // wait for a second
 digitalWrite(Nitinol3, HIGH);   // set the first leg on
 delay(1000);              // wait for a second
 digitalWrite(Nitinol3, LOW);    // set the first leg off
 delay(1000);              // wait for a second
}

Video of Shape Changing Textile >>>

Video #2 >>>

I started out prototyping on one piece by attaching the nitinol by sodering it to conductive fabric. I then tested this by using alligator clips and attaching it to my battery to make sure that I can achieve the movement that I was looking for in the square of felt. Based on the properties of the 0.006mm nitinol, since it needs ~410mA to achieve 1 second of contraction and I was using a 3.7V battery, I calculated, using Ohm’s law, that I needed approximately 9Ω of resistance in my connection from the nitinol to the power supply.  The resistance of just the nitinol and conductive fabric was only ~5Ω so I added four additional 1Ω resistors to the connection.  I tested this, and I was not achieving as much movement as I would have liked so I removed one resistor and it seemed to move better. I recalculated the total resistance at this point and it was actually closer to 9Ω while before it was closer to 9.8Ω.  I repeated the same on the other square but used all four resistors because my measurements using my multimeter indicated I needed slightly more resistance. Perhaps my nitinol was a tiny bit longer.

I connected both squares to the mosfets and then connected them to separate Arduino pins.

Finally I programmed it so that the pink and purple “kites” alternate in their movements every few seconds and speed up in their alternations. They then progress to slow down again.

Here is my work in progress:

I added some accents (bows) on the kites to make them look more visually appealing and I also cut off some felt from the sides of the pink kite to see the effect that reducing the weight had on movement (moves up slightly higher).

Here is the finished product and accompanying video:

Calculations:

Required resistance: 3.7V/0.41Amps = 9.02Ω

I designed the shape in Solidworks in sheetmatal format so I will be able to flatten in and cut it on the late cutter:
the design in CAD

Here is the drawing of the flat caterpillar to be cut in the laser cutter

Laser cutting

I cut the traces of the vinyl cutter

Then I attached the traces on the cuter cardboard

I used water vapors to bend the cardboard and maintain it’s flexibility

This is images of the final piece