@Barhandar  
I guess it depends on what you want to see that helps you to enjoy the image. I see them as being captured, and I’m guessing Archite does too. Don’t really matter one way or another, it’s still a great pic with an amazing concept.

@Archite  
I think it would be more of an issue reaching them. It doesn’t look like they have a lot of wiggle room in that position.

@Archite  
Why do you think they’re held prisoner?  
I’m sure it’s voluntary and they’re greatly enjoying each other’s company.

I don’t know what’s more deliciously insidious…The mechanism and such, or the fact they’re bound in such a way that if they could just see the clips holding them prisoner, they’d be able to easily free themselves.  
I mean, they’re these sort:  

@Dimondium  
I suspect that 1:1 means 1 cycle per day, 2:1 means 2 cycles per day, and so on (so it gets faster, not slower, on higher settings).  
The reason being, 1440 cycles per day means one cycle per minute, 288 is one every 5 mins, 96 is one every 15, 48 is one every 30 mins, and 32 is one every 45 mins. I can’t think of any other reason to have such arbitrary increments.
 
(Yes, I am a huge nerd)

The controls remind me of Myst.

“Guh.” Luna gagged from the thick dildo that rested just far enough into her mouth to be uncomfortable, touching the top of her throat. The thing was wet with her own drool that dripped down onto her bare breasts periodically, every drop making her feel more and more helpless. Not that the feeling wouldn’t have been present otherwise. Black cords connected to the floor and pulleys around her held her in place while a spreader bar jingled between her legs, as if it was playing some sweet symphony of humiliation to the moon princess. When she’d first awoken in this state, she’d struggled and squirmed until her body was damp with sweat, defiance that would make Nightmare Moon jealous flashing in her eyes. But it was all for nothing. It hadn’t helped her. She’d given up by now.
 
Apart from the padded leather cuffs that held her, she was completely nude. The flowing, deep blue, translucent silk nightgown she’d been wearing whilst sleeping in her bed back in the castle, before she was kidnapped, was gone. So too were the lacy undergarments she loved, that hugged her most private and sensitive places with their oh-so-soft touch throughout her slumber. Now, those places that no one but her had ever the privilege of seeing before were bare and unshielded from whatever eyes lurked outside her vision. But even being totally unclothed wasn’t what filled her with embarrassment and humiliation the greatest. No. It was the ring. A perfectly crafted inhibitor ring, set with precious stones and heavily enchanted, gracefully rested on her horn. Something so tiny, so insubstantial, was nevertheless able to render her mighty Alicorn magic powerless. No matter how hard she concentrated on the simplest spell, the gems just dimly glowed and nothing but a few useless sparks flew from the tip of her horn. She was a princess! She was one of the most magically gifted beings in Equestria! She’d made the whole world tremble a thousand years ago with just a casual flick of her horn! And now, to have a simple piece of jewellery strip that all away from her and leave her like a dull Earth Pony: it made her feel indescribably helpless.
 
Her mind was brought back to reality by a muffled, but noticeably loud, unwilling moan from mere inches away. Feeling sorry for herself had made her all but forget that her big sister was in the same state, cords holding them in an inescapable, incestuous kiss while the dildo filled both their mouths. From her white thigh, a cable ran between Celestia’s legs, connected to a small bead that lay nestled between her private folds. There it hummed and vibrated, forcing the basest of pleasures upon the sun princess. The smell of her damp excitement danced over Luna’s nose, filling her face with a deep blush. Though Celestia tried to keep some small nugget of dignity, she moaned just like any other pony as the mare-toy played her like an instrument. Luna had a similar device attached to her thigh and leading to the one place she wished it didn’t, but it was still and silent for now.
 
Luna was reminded about the mechanism that their captor, or captors, used to torment the sisters. The first part was a clock-like device, magically enchanted to perfectly show the time of day. It was connected to a brass slider on a scale, one side showing the sun with markings going from 10 to 0, and the other side showing the moon with markings from 0 to 10. The slider was what controlled the vibrators. The sun and moon corresponded to each princess, and the number was the intensity of the device. The mechanism was set up so that during the day, Celestia’s vibrator was on high, while during the night, Luna’s was on the same setting. The more intense one sister’s device, the less intense the other’s. What made the whole thing so cruel was the princesses’ connections to the sun and moon, and so the time of day. Even with their horns nullified, their natural affinity allowed them to still raise and lower their respective celestial body. Therefore it was up to each sister to decide when to switch the sexual torment to the other. Celestia, protective as she was of her younger sister, had done her best to spare Luna, keeping the sun high in the sky. But now it was getting too much. The humming vibrator was clouding her mind, and all she could think about now was stopping herself from having that fifth forced orgasm grace her aching nethers.
 
“I’m sorry, sister.” Was what the sun princess meant to say, but it was transformed into a mess of half-syllables and drool from the ring gag and dildo. Unable to look at Luna, Celestia’s eyes turned to the window in humiliation, watching as the light dimmed, ashamed that she was lowering the sun so selfishly. The clock turned, clicking as the sun side turned to make way for the moon side. The slider descended as it did. Luna’s eyes went wide as she gazed at the device, seeing it slowly change to the same symbol that rested on her flank. Her arms, locked around behind her sister’s back, just as Celestia’s arms were tied behind her own, squeezed desperately against the sun princess’s bare breasts, her hands grasping at white feathers. Brass jingled against brass as she struggled, hearing the humming between her sister’s legs soften, while feeling the humming between her own grow. Luna tried to beg her sister, but nothing except animalistic groans left her lips. Was this going to be it? Saving herself and fighting her urges for so many years. How could Celestia do this to her?! She knew how much the moon princess treasured her pure, untainted virginity! Moments later, Luna felt herself growing damp, her lower lips turning pink and puffy from anticipation for the feeling that had been denied to them for over a thousand years. Being so inexperienced, Luna didn’t stand a chance resisting her body.
 
Her first ever orgasm covered the floor in her nectar, filled the air with her loud moans that lacked any of a princess’s decorum, and embraced her mind with alien pleasures, compared to which even seeing her sister again after her lunar imprisonment felt like nothing. Why had she ever been so stupid as to keep herself from this for so long? What was something as silly as “purity” when compared to this joy?

Huh…interesting. I think that dial on the left controls some sort of wireless vibrator, but in an interesting way.
 
As the day/night cycle goes on, their vibration levels probably get adjusted. But seeing as the “10” to one side is another’s “0”, I think it’s sort of a “moment of glory” system. What puzzles me is I’m not sure which is which. Whether it being high noon makes Celestia’s vibrator at full power and Luna’s at zero (or close to zero), or vice versa, I’m not sure. The pointer is kinda unclear to me.
 
But then that slider with (X):1 is probably “hours per complete cycle”, and setting it to 24:1 means “a full day is a full cycle”. If so, then there’s options to divide it into 1/24 day cycles, 1/12, 1/6, 1/2, 1 (current setting), 1.3333, 2, 4, 12, or 60 day cycles. The upper 3 of which have very dark and/or sexy undertones. How long are they actually bound if those settings apply how I’ve posited? Is this consensual and/or planned, or the plan of some devious kidnappers to keep the princesses trapped in orgasmic bliss until the end of their very long lifespan?
 
If I’m right, that is so mechanically awesome and sexually devious that it is HOT to the nnf degree.
 
This gets my fave and uh…“attention”. Even if this wasn’t intended, the setup is amazing that it allows for this kind of headcanon to be plausibly possible.

So the pulleys in front and behind them pull their knees up into the other one’s crotch, and the ones left and right of them pull on their elbows, making the distance between their shoulders closer, meaning more boob squishage.

@Narlepoax III  
Presumably vibrator/pulley control.

I would love to know what kind of setup this is.

I have no idea what the hell this machine is supposed to do, but Luna seems to be enjoying herself; even if it’s to Celestia’s detriment.