Chen Hao stared at the numbers flashing on the screen, his fingers unconsciously picking at the crack on the edge of the terminal. The "System self-check complete" message had been silent for ten minutes, but he still didn't dare let go.
"Are you sure you don't want to restart it?" he asked.
“It’s already running.” Nana pushed the sensor half an inch further toward the riverbank. “What you’re seeing now is real-time data.”
"Oh." He nodded, then shook his head. "But it's not making a sound."
"The water is moving, so it is moving."
He squinted at the river; the wind tore the ripples into diagonal lines, like scratches made by a fingernail on glass. In the distance, a withered leaf twirled past, not fast, but it didn't stop.
"So... are we waiting for the leaf to crash into the wheel?"
Nana ignored him and pulled up the 3D graph. A blue-green velocity distribution map appeared on the terminal, varying in shades, like someone had spilled a box of paint in water. She pointed to an area on the edge of the main channel: "Here, the average impact force is 37 percent higher than in the simulation tank, and the turbulence frequency is stable, making it suitable for starting low-speed blades."
"I don't understand." Chen Hao scratched the back of his head. "Just tell me, are we moving to the left or the right this time?"
"Twenty meters ahead."
"Let's go!" He grabbed the canvas bag from the ground, stuffed half of the terminal inside, leaving the other half sticking out and dangling. "Let the waterwheel meet its master!"
The two walked up the riverbank. The mud was soft from last night's rain, and their shoes sank in half with each step. Chen Hao walked unsteadily, humming a tune he had made up: "The water flows and gurgles, the wheel turns and turns, if it doesn't stop, I'll stew it for dinner."
Nana glanced at him: "Waterwheels don't contain protein."
"What a pity," he sighed. "I was hoping to try teppanyaki."
Upon reaching the designated location, he tossed his bag to the ground and began assembling the new model. This time, the blades were pressed from recycled alloy plates, their edges retaining the curves left by the mold, unlike the previous ones which were shaped by hand. The bearings were also salvaged from old equipment, ensuring they wouldn't emit a groaning sound as they rotated.
"Is this design really going to work?" he asked while tightening the screws. "Why does this blade look a bit like a pancake spatula to me?"
“A 12-degree tilt angle provides optimal flow efficiency.” Nana took the connecting rod he handed her and inserted it into the shaft. “Besides, the pancake spatula can also generate electricity, as long as you’re willing to turn it.”
“That makes sense.” He grinned and patted the wheel. “Then you’re my electric shovel auntie.”
It was noon when the assembly was completed. The sunlight slanted across the river, reflecting a patchwork of shimmering silver light. Chen Hao crouched down, inserted the support frame into the silt of the riverbed, and moved a few stones to weigh down the base. The newly made guide vane dipped into the water, resembling an outstretched hand.
“Come on.” He took two steps back and rubbed his hands together. “Let’s see if water is more powerful, or if this lazy person like me is more powerful.”
The water pump started, and artificial water flowed along the guide channel towards the bottom of the blades. At first, it was just a light touch, and the wheel trembled slightly, like a yawn. Then, a second and a third wave followed one after another, and the blades began to rotate slowly, one revolution, two revolutions, and then suddenly accelerated.
"It moved!" Chen Hao jumped up, almost stepping into the water. "It really moved! It's not stuck spinning, it's spinning on its own!"
The connecting rod swung, causing the small grinding disc at the other end to move back and forth. The dry slag in the stone trough was crushed little by little, and the dust rose with the rhythm, only to be blown away by the wind.
Nana stared at the graph on the terminal, her lips twitching slightly—if robots could laugh, it would probably be about this magnitude.
"The engine speed is eighteen revolutions per minute, and the output power reaches 89% of the expected value," she said. "The power transmission is stable, with no obvious vibration."
"Eighty-nine?" Chen Hao frowned upon hearing this. "Then we're still short eleven? Did I skip a meal of compressed biscuits and not get enough energy?"
“The counterweight is insufficient.” She pointed to the axle. “Adding a 200-gram balance weight should allow it to pull over 95.”
“Okay, I’ll weld it right away.” He rolled up his sleeves and took out a welding torch and a piece of scrap metal from his bag. “Keep an eye on it. If I get excited and weld it crooked, this car will have to do a tap dance on the spot.”
The moment the flames erupted, the river wind suddenly picked up, causing the terminal screen to flicker. Nana raised her hand to shield her eyes, and when the image returned to normal, she noticed the rotation speed had dropped three revolutions per minute.
“The wind won’t have much of an impact.” She adjusted the angle of the support frame, “but I suggest speeding up the welding process to avoid prolonged interruptions in transmission.”
"It's a race against time." Chen Hao squinted at the interface, and just as the solder joint was halfway down, the grinding wheel suddenly stopped, and the connecting rod got stuck.
"Again?" He flicked his scorching welding torch. "Who's trying to trip me up now?"
Nana quickly checked the connection: "The gap between the latches has widened by 0.4 millimeters, which may be due to slight changes in the metal caused by thermal expansion and contraction."
"Then what do we do? Grind it again?"
“No need.” She took a thin metal sheet from her toolbox. “Just add a compensating pad for temporary repair.”
The two worked together to make the adjustments. On the second start, the water flow propelled the blades more smoothly, the millstone started spinning again, and the rhythm was steady without stopping.
Chen Hao slumped onto a rock on the shore, panting, and said, "This thing is more precious than my life; it needs maintenance all the time."
"Your heart rate is currently 112, which is indeed not as stable as it is."
"Thanks for reminding me." He rolled his eyes. "I'll try to learn it next time, to breathe at a steady pace."
As the sun began to set, they had already recorded four complete sets of operational data. The wheel maintained a rotation speed of over eighteen revolutions per minute, and the millstone never stopped. Only a thin layer of slag remained in the stone trough, almost completely ground into powder.
"It's done." Nana closed the terminal. "Model verification passed, technology closed loop established."
"So..." Chen Hao stood up, brushing the mud off his pants, "we really used water to get things done?"
"To be precise, it's about converting kinetic energy into mechanical work." She paused. "You can also think of it as—the water doing the work for you."
He laughed, bent down, picked up a small pebble, and skipped it across the river. It sank to the bottom after three jumps.
"So, does that mean I can lie down and have it do all the work for me? Like, it can move bricks, cook, and do laundry for me?"
“Theoretically possible,” Nana said, looking at the still-turning waterwheel. “Provided you build one big enough.”
"Big enough?" His eyes lit up, then he lowered his voice, "You know... could we make a giant one and hang it in the middle of the river, so it can generate electricity for me every day?"
“We need to survey the river’s carrying capacity.” She turned to the downstream section of the river. “We also need to assess the structural stability and maintenance costs.”
"Oh, you're making it sound like we're really going to start work." He waved his hand with a laugh. "I was just saying it offhand."
Nana didn't reply, but simply reopened the terminal and brought up a new terrain overlay map. Her finger hovered over a certain point for a few seconds, then gently tapped it.
The marker lights up.
Chen Hao leaned over for a look, and just as he was about to speak, he suddenly noticed that the waterwheel's rotation had slowed down.
"Why has it dropped again?" He immediately became nervous. "Is there going to be another problem?"
Nana stared at the curve, her brows twitching slightly.
“It’s not a malfunction,” she said. “The water flow has changed direction.”
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