This bend sensor actually reacts (decreases in resistance) to pressure, not specifically to bend. But because it is sandwiched between two layers of neoprene (rather sturdy fabric), pressure is exerted while bending, thus allowing one to measure bend (angle) via pressure. Make sense? Watch below:
So basically you could use most any pressure sensor to measure bend, but this one I find gives me the best results (sensitivity) for measuring the bend of human joints when attached to the body. It is sensitive enough to register even slight bend and has a large enough range to still get information when the limbs are fully bent.
The resistance range of this bend sensor depends a lot on the initial pressure. Ideally you have above 2M ohm resistance between both contacts when the sensor is lying flat and unattached. But this can vary, depending on how the sensor is sewn and how big the overlap of the adjacent conductive surfaces are. This is why i choose to sew the contacts as diagonal stitches of conductive thread - to minimize the overlap of conductive surface. But only the slightest bend or touch of the finger will generally bring the resistance down to a few Kilo ohm and, when fully pressured, it goes down to about 200 ohm. The sensor still detects a difference, right down to about as hard as you can press with your fingers. The range is non-linear and gets smaller as the resistance decreases.
This sensor is really very simple, easy to make and cheap compared to buying one. I've also found it to be reliable enough for my needs.
I am also selling these handmade fabric bend sensors via Etsy. Although it is much cheaper to make your own, purchasing one will help me support my prototyping and development costs >>
This neoprene bend sensor is also featured on the CNMAT resource site, among other great possibilities for making your own bend sensors >>
To see this sensor in action have a look at the following video. The dancer has fabric bend sensors (the same as this Instructable shows) attached to her: Underarms, elbows, wrists, shoulders, hips and feet.
There is a Bluetooth module on the dancer's back that is transmitting all of the sensor information to a computer that is then triggering instruments (LEMUR's musical robots) to play. For more info visit:
There is another video at the end of this Instructable that shows you it in wearable action!