Help me install sensors into a mannequin for, well..rope bondage
January 16, 2015 12:53 PM   Subscribe

So I'm a Kinbaku (Japanese rope bondage) enthusiast (Wikipedia's page on Kinbaku). I've been studying it & taking lessons fairly intensively over the past year, and really fallen in love with the artform. A couple of months ago, I picked up a cloth mannequin and added in a PVC skeleton with wire joints so that I could practice on it. Here's where you come in: Can you help me figure out how that mannequin can tell me - numerically - how tightly I'm tying it?

Why I'd like a pressure readout:
One of the hardest to develop skills in Kinbaku is the ability to accurately and reliably control rope tension. Basically, if you wrap a rope around someone's torso a couple of times and then add a knot, those ropes can be anywhere from Nearly Falling Off to Crushingly/Dangerously Tight. If you want to be good at this, you need to be able to apply rope at any level of tension within that range. If I can get numerical feedback from my practice dummy, that'd help me get much better at controlling tension.

Where I'd like a pressure readout:
In most standard Kinbaku ties, the arms are crossed behind the back, the wrists are tied together, and then the rope is wrapped 4 times around the upper half of the upper arms (roughly at armpit level), and 4 times around the middle of the upper arms (a bit above the bottom of the sternum). You can see that basic construction over here(No nudity, but I guess some workplaces might frown on it).

My goal is to figure out how tight those upper 4 wraps are, and separately, how tight those lower 4 wraps are. I figure there must be some way to install a pressure/compression sensor into the dummy at those spots and give me a numerical readout.

Mechanical/Electrical expertise:
Please tailor instructions for someone technically minded, but not an electrical engineer or an experienced programmer. I've soldered stuff onto circuits before, I can follow detailed instructions on how to build devices/circuits, I know my way around a computer, and I took 1 semester of C programming (don't remember much, but understand the rough basics on how programming works). Happy to work at this and do research if you send me in the right direction (and ideally if you send me to tutorials), but would appreciate more details than "Just program an Arduino to do it"

Other possibly relevant thoughts
While it'd be nice to install these pressure sensors directly into my mannequin, it's not entirely necessary; if there's a way to rig sensors to a *roughly* torso-sized object that has a bit of give to it [stiffness between, say, a firm pillow up to firm rubber, but not as stiff as hard metal/wood], it'd be enough to let me practice tension. Thinking about it now, if there's a way to build an "H" out of wood (||------||), stick a sensor in the middle of that "H" (||----x----||), and then wrap that whole assembly in fabric or rubber or something until it has the size/elasticity of a torso, then that'd be enough. So if nothing's coming to mind with the full mannequin, how do I do *that*? What kind of sensor would I need, how does it work (How would you use/mount it to measure the compression in the middle of that "H"?), and how do I get a number out of it?
posted by anonymous to Technology (3 answers total) 3 users marked this as a favorite
 
Perhaps this is a question you want to post on Fetlife (if you haven't already)?

Maybe make your mannequin out of memory foam or some other material that measures pressure.
posted by danceswithlight at 2:11 PM on January 16, 2015 [1 favorite]


I don't know anything about Kinbaku or knots and am not great at this kind of project, but do you know about flex sensors? They're not exotic, inexpensive and common enough. It's a strip of plastic with variable resistance depending on how much the strip is bent. They're quite sensitive, I imagine if you align it under the rope with a bit of padding it might do a good job telling you how tight the rope is.
posted by Nelson at 7:39 PM on January 16, 2015 [1 favorite]


I think the search term you are looking for is 'surface force sensor'. This will help you find the tightness of the ropes. Compression sensor measurements would only be useful internally, say along the spine or behind the ribs of your 'skeleton'. Flex sensors would only give a useful measurement if aligned along , either over or under, the ribs; and torsion or deflection do not neccessarily equate to pressure. Each of these will require a different set of equations and then be used together in a fourth set to get the level of detail you desire.

I don't currently have enough free time to offer detailed instructions for using them; but check out this product and, indeed, their entire line looks useful to some degree or other. Once I do have some time free I'll revisit this and, if no one else has found you an answer, see if we can't figure out a working method.
posted by schade at 9:06 PM on January 16, 2015


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