by lefroyobunny

A “wallflower” is someone who is shy, and who no one really knows. But that person can be some of the most interesting people we have ever met. This project is a tribute to those seemingly shy, yet extraordinarily interesting people.

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.