Hey! So I've built a very rough proof-of concept model of the SkeinTwister. This is the first version - just a foot pedal that connected and disconnected power to a motor. Here's a video of it in action, so those of you not familiar with the Wonderful World of Yarn have some idea of what I'm talking about:
A few dyers I talked to were interested in the ability to twist a skein exactly the same number of times each time, automatically. This thought percolated in the back of my mind for a while. I certainly could instrument it with a rotation counter, and dyers could use it with a SkeinMinder. But I felt that this wasn't the right solution. Even though people were asking for the same number of twists, what they really meant is that they wanted each skein to look and feel the same.
If each skein is exactly the same, this equates to number of twists. But the reality is that yarn is practically a living thing that hates to stay put. During dyeing, sometimes loops will get snagged, causing the skein to get a little out of whack, and need a different amount of twist to look tidy. Also, skeins will actually measure slightly different circumferences, depending on how far out on the winder arms they were initially wound. Not to even mention that it's difficult to keep perfectly consistent winding tension over different winding sessions. The upshot is that hanks will require different amounts of twist to look and feel consistent when in their final twisted put-up.
So if there were just some magical way to measure the force it takes to wind a skein.....good thing DC motors are pretty magical in that force = current. The second proof-of-concept has a current sense amplifier fed into a comparator on an ATTiny85 processor. The other side of the comparator is hooked up to a trim pot (knob), so the user can adjust the "skein firmness" and wind consistently, no matter how the skein is prepared.
A video demonstrating the automatic stopping capability: