Curling flower

by rbatzer

My idea for the Shape Memory Alloy assignment was to make a curling flower that would react to light by opening up.  I started by making several prototype petals to see how well my idea would work. I experimented with fabric and paper petals and used a power supple to test how well they curled.


Fabric Petal

Paper Petal

I wanted to have at least five petals to make a complete flower. I found that the amount of Nitinol we were provided with would not be enough to make the flowers curl completely like the longest section of demo from class. I decided to settle for slightly scrunched petal tips which I did have enough Nitinol to achieve.

Each petal needed 2.5 inches of Nitonol, so I was able to make six petals. I tested my first complete petal as shown in the video below to find out how much resistance each flower had. A 2.5 inch piece of Nitinol nominally has 3.5 Ohms of resistance. I measured one petal at 410mA and 1.2 V for 2.9 Ohms per petal. I decided to connect three petals together and use 3.7 volts from the LiPo battery. I used wire for my power connections to limit other possible power losses.

Parts for the final flower

The petals are connected in sets of three. They are connected positive to negative by a wire soldered between each petal as seen in the third picture. The first picture shows a stiff fabric ironed onto the back where the Nitinol wire goes which prevents the fabric from crumpling and forces it to bend.

The leaves are just for decoration and hold the button to turn the MOSFET for the petals “on”. The wiring in the leaves is stitched into the middle of the felt so it will be electrically isolated.

The final flower is assembled below. All the electronics are houses under the lilypad in the flower center. This produces a clean look, but the electrical connections ended up very jumbled and are difficult to debug. I forgot to account for the diode voltage drop at the MOSFET, so I ended up using the 5V supply from the laptop instead of the 3.7 V from the battery.