Grasshopper

algorithmic modeling for Rhino

Does anyone have know how to write to Flexinol? 

I have a circuit set up which uses an IR Proximity Sensor as the input. I attempted to write to the SMA by using PWM Values (0-255) I've also tried Digital Values (0-1). I don't get any response that is based on my input. I can flex the wire when I "hardwire it" but no actuation response.

 

Help!

 

Thank

 

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Hi Ivan,

In my experience, you can't trigger a SMA actuation (unless you're using custom calibrated alloys, which is another topic all together) unless you're using an external power supply.  Basically, you need to supply enough current to the SMA in order to heat the wire up to it's Austenite threshold.  The Arduino pin can only supply roughly 40-50mA of current, which isn't enough.  Typically, what you need is circuit setup (either a transistor, MOSFET, or relay) where the arduino pin will act as a switch to allow the current to flow through the circuit or not.  A friend of mine, Jie Qi, from the MIT Media Lab wrote a very good introduction to using SMA's with electronics.  You can find it here: http://fab.cba.mit.edu/classes/MIT/863.10/people/jie.qi/flexinol_in...  Using this circuit, you should be able to send a digital signal (HIGH/LOW) from Firefly to trigger the SMA wire.  I don't think you will need PWM for this application.  I hope this helps.

BTW, I looked at your last image (FFwrite.jpg) and it looks like you're feeding a list of values into Pin11... there's no need to do this (in fact, you should only supply a single value to each pin as this all that it can handle).  Just thought I would give you a heads up.

HTH,

Andy

Andy Thanks a bunch...

Jie's projects are pretty cool. I ended up using a transistor as you suggested. The Arduino's current was enough to actuate just one strand of Flexinol without an additional power supply.

I posted a Video of the experiment on my blog. I'll post some images and screen shots on here later...

 

Thanks a mill!

 

Ivan

Nice.  I'm glad you got it working.

Cheers,

Andy

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