Nitinol
During my internet research, I came across these experiments using Nitinol, a shape changing metal alloy that contracts when heat/current is applied to it. What interests me about this material is the architectural implications for a structure that may open/close or respond to the presence of a person. The following links are experiments other people have done using nitinol
During my internet research, I came across these experiments using Nitinol, a shape changing metal alloy that contracts when heat/current is applied to it. What interests me about this material is the architectural implications for a structure that may open/close or respond to the presence of a person. The following links are experiments other people have done using nitinol
Flexinol vs Muscle Wire:
Flexinol
Contraction and relaxation depend solely on the temperature of the nitinol alloy wire. Any method of heating and cooling the wire may be used. Nitinol wire has a high electrical resistance, approximately 1.25 ohms resistance per inch for the 6-mil wire. The resistance of the wire to the electric current quickly generates sufficient heat (ohmic heating) to bring the wire through its transition temperature. So many times an electric current is passed through nitinol wire to heat the wire electrically. When the material is allowed to cool, the wire can easily be stretched back it its original length.
Nitinol wire usually has a counter-force applied to it in the opposite direction of its contraction. The counter force resets, or stretches the wire back to its original length when in the low temperature phase. This is called the bias force. If the nitinol wire is brought to its transition temperature without a bias force it will contract, however, when it cools it will not return to its original length
Although it is possible to buy Flexinol pre-crimped, in most cases the hobbyist or student must crimp the wires themselves. The hair-thin nature of most Flexinol gauges makes crimping difficult, but it is certainly possible to get a good crimp with hand tools. There are many potential approaches. In the original Stiquito plans, Mills ties a small, loose knot in the wire and crimps with a section of 1/16 inch aluminum tubing. Roger Gilbertson, author of the Muscle Wires Project Book, recommends the N-scale rail joiners which are used to connect model railroad conductive track. Many builders will use standard solderless terminals from other electronics applications. A good and simple solution for a temporary crimp that can be repositioned is to use standard machine screws and hex nuts.
Flexinol in most applications uses electricity to generate the internal heat needed for transition. Proper control of the current is essential for satisfactory results. Too little current and the wire will fail to contract. Too much current and the wire will overheat, becoming stressed and losing its shape memory properties. In between too little and too much, variations in supplied current will affect the heating and cooling times. In the table reproduced below, Dynalloy provides some guidelines as to how much current is required to cause a Flexinol wire of a given gauge to contract in one second. Also provided is the approximate electrical resistance of the various gauges. Note that Flexinol has fairly high resistance compared with copper wire and other common conductors. In some applications it is possible to activate the wire without additional resistance in the circuit. A 0.005" diameter wire has a resistance of about 1.9 ohms per inch and needs about 320mA to reach its transition temperature - to heat a 5-inch length of 0.005" Flexinol will require about 3 volts which could come directly from two standard AA batteries. (Volts = Resistance in ohms * Current in amps.) Of course Flexinol is hungry for current and it would be easy to overload a wire. If above there were 2 inches of wire rather than 5, that same 3 volts would deliver 1.58 amps and likely destroy the Flexinol.
Flexinol in material
Wearable
Creating a wearable electronic piece presents problems as the piece has to be first and foremost safe (not going to catch fire or electrocute the wearer), and presents further problems with how the electronics, battery components etc will be integrated into the clothing.
Some links that look at wearable pieces are:
The Galaxy dress an amazing LED dress
Little Boots' Cyber Cinderella Dress
The Flora Lux Sensor - Wearable light sensing
The Dandelion (mentioned earlier)
xslabs Youtube videos
Sarah Laynes blog, in particular this sound reactive nitinol dress
Wearable research and projects by Jovana Ivanovic
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