The explanation is quite simple. The overturned Y has a dildo-sleeve ( Like the ones you can get to change the 'cover' on a vibrator) on the one end, and a set of ankle-cuffs on the two other ends.
The 3 sticks are assembled by hinges, so that the dildo will move into her vagina, when she assembles her legs, and out when she's spreading them..
It's necessary to add a piece of string or chain between her ankles, to prevent her from spreading her legs so much, that the dildo 'drops out'.
I have had the opportunity to test the gizmo, but unfortunately, I had no chance of getting either photos, or a video of it, that's why I've made the animation, by cutting and pasting from a wide range of sources !
The Y is made from 3 sticks,( i.e. 25 mm thick ); 2 hinges, a dildo-sleeve,
2+2 screw-eyes, a piece of line/chain, and 2 ankle cuffs.
1/ Cut two (identical) pieces of stick, reaching from the ankle, to a little
above the knee.
2/ Mount the hinges on either stick, at the one end, and mount a screw eye at
the other ends.
3/ Cut another piece of stick, so long, that it'll reach from the ends of the
first two sticks, to her vagina + 15 centimeters, or more, if she likes
it.
4/ round off the one end of the last piece of stick (which goes inside her
vagina)
5/ Mount the hinges to the other end of the dildo-stick, one at either side.
6/Mount the remaining 2 screw eyes, on the inside of the two sticks to be
attached to her ankles ( facing one another ).
7/ Pull the dildo-sleeve over the rounded end of the stick.
8/ Strap the ankle cuffs to her ankles, and let her stand with the feet so far
apart, that she'll have about 5 cm of the dildo inside her vagina, when you
attach the screw eyes at the 'bottom-ends' of the sticks to her ankle cuffs..
9/ Bind the line (chain) between the screw-eyes on the lower sticks, to prevent
her from 'loosing' the dildo by spreading her legs. ( it needs to be rather
tight ).
10/ Now you've secured that she'll be fucking herself whenever she's walking.
Now, when she's walking, the dildo will a): slide in and out of her vagina,
and b) rotate inside her vagina...
Now, dress her up in a long skirt, and take her for a walk in the forest,
shopping or...
PS: wearing this contraption, she will not be able to sit down !
Well, finally I got myself pulled together, to try to make a male edition, of
the overturned Y, which 'acts' on the cock, in stead of 'acting' inside the
vagina.
It is - however - not an instant success, but I've got an idea, which might make
it a success, and I'll try to get that into the real world, as soon as possible.
I've made a video, of the male overturned Y, which you'll find here: 