Well, there's three ways to move heat around. From fastest/most efficient to slowest/least efficient they are, convection, conduction, and radiation. Convection only happens in a liquid that is allowed to "roll" - that is, to move freely. A circulatory system uses conduction (between tissues and blood) and then moves the blood to a new area to repeat the cycle. A solid body (like a sex doll's skin) uses traditional conduction which is much slower.
You skipped a step there when you said "contains body temp water." The question is how you heat the water to body temp uniformly. Conceptually, you've got one or more heating elements in the robot. For the sake of argument, let's imagine we produce heat through electrical resistance with a unit mounted in the chest cavity.
As an aside, another commenter suggest running coils of wire throughout the body to produce heat. That would also be heat through electrical resistance ...so that guy was implying that just below the skin, over the entire body, we are running fairly large amounts of current. I didn't reply to that post, but I laughed at how dangerous that would be, to say nothing of the electromagnetic effects (the coils will produce a magnetic field). Super bad idea.
That's it! That's the step I'm concerned about.
Our hypothetical design has a heating unit, surrounded by a fluid (water) held in place by a porous substrate (a sponge layer). The problem is, the water in this system will not form convection currents. Thus, the heat will only be distributed through conduction. I think you're going to find that's very slow.
You can test this system by heating water to a boil in a shallow pan, and placing a soaked sponge upright in the pan, like this:
View: https://i.imgur.com/6HZodcr.png
Note that the rising steam around the sponge will be very hot, but that's irrelevant to what we're testing. The question is, how long does it take for the water in the top of the sponge (analogous to the surface of the skin of the robot) to heat up? How long would it take for the heat from our heater in our robot's chest to be perceptible at say, her elbow?
After leaving the sponge in the boiling water for a bit, take it out and lay it flat on the counter. The part that was in the boiling water (the end where my finger is) is very hot - a bit painful to touch, in fact. But the water in the other end of the sponge is still quite cool:
View: https://i.imgur.com/bmeFX2S.png
In other words, the temperature gradient is rather large. We'd have to make the heater in her chest really hot (dangerously hot) in order to have body-temperature temperatures at her shoulder. And we'd have to make it hotter still so that it was dangerously hot at her shoulders in order to make her elbows warm. There's really no chance that we could make her fingers acceptably warm this way.
So, I really think you have to move the fluid around for this to work. Maybe, since the subcutaneous layer is spongy, you could move it around just by having her move around - squishing the water back and forth. I don't know.
The time tested way to solve this problem is with a circulatory system. Tiny hoses could move the fluid (and the heat) right down to her fingertips. That's technically possible and I'm convinced it's the most efficient proposal. I'm just saying that it's complicated and expensive.
Of course, my cell phone is also complicated, but it's no longer all that expensive. Capitalism and economies of scale have brought the price way down. Maybe there's a future where everything is automated and AI runs the world (think, the Culture series by Ian Banks) and humanity has essentially infinite productivity available to it, such that a sex robot as complex as a stealth bomber is feasible to produce and is given away to people for free.
I can dream, right? My only point is that under current economic conditions, most people's expectations (a sexbot that is indistinguishable for a human) is not going to happen.
Yes, I was thinking the problem was less the movement itself and more about how that movement is achieved - specifically, do we have a robot that can move, but doesn't have the shape of a woman; do we have a robot that can move, but makes loud noises or moves in unnatural ways (like jerky, or even super slow movements).
The chief requirement is that it be pleasing to the eye (and other senses). It has to be attractive. If we have actuators and motors that can duplicate human motion, but it doesn't fit into the body of an attractive female, then it's not a successful sex robot.
I wasn't familiar with that, but googling found this:
View: https://www.youtube.com/watch?v=ER15KmrB8h8
And that looks very promising.
It occurs to me that, so long as you're not changing sex positions, VR (not AR) is probably the best thing you can get right now. Just lay on your back and, through VR, you see a girl on top of you, but in reality, it would be a machine that doesn't look like a girl at all.
Which brings me to the other problem that I brought up, here: https://incels.is/threads/ai-with-reasoning-capabilities.259097/#post-5943642
The way corporations ruin everything. The reason you aren't using VR to watch porn right now, is that the makers of VR hardware insist on tightly controlling the software. You have to have a facebook account to use occulus, for example. There are stories of people who had their facebook account banned because they said maybe orange man isn't so bad - and then they lost their ability to play any VR games.
Facebook doesn't want oculus to be associated with porn, so there's no easy way to get what I described above. I'm sure there will be in the future but that's not the point. The point is, even if you solve all the technical hurdles, corporations want to give you sex robots that collect data on you, push ads, force you to upgrade, etc.
