The night wind whipped the snowflakes along the ground as Chen Hao, his neck hunched, walked towards the workshop entrance. He carried a metal plate in his arms, its edges still covered in ice, and his fingers were red from the cold. Nana followed behind, carrying reagent kits and data disks she had brought back from the research station.

"The lock is stuck again." Chen Hao nudged the metal door with his shoulder a couple of times, the hinges screeching as they finally opened a crack. He squeezed in sideways, placed the metal plate on the workbench, and breathed a sigh of relief. "This crappy place is even colder than outside."

Nana came in and closed the door behind her. She put her things down, walked to the furnace in the corner, squatted down, and checked the fuel tank. "The ethanol supply is enough for three hours, but the temperature isn't reaching the ideal level."

"Then add something else." Chen Hao took off his gloves, rummaged through the toolbox, and pulled out half a bottle of engine oil. "It's leftover from when I disassembled the sled rails last time. Let's make do with it."

“I don’t recommend mixed combustion,” Nana said. “It will cause carbon buildup, which will affect heat transfer efficiency.”

"We don't need to be so fussy." He poured engine oil into the fuel tank. "As long as it burns, it's fine."

After the fire was lit, the room slowly warmed up. Chen Hao rubbed his hands and sat down at the counter, picking up the metal plate and examining it from all angles. "You really think this thing can be used for reinforcement? What if it cracks halfway through the trip after we install it?"

"Mass spectrometer analysis confirmed that its tensile strength is 1.8 times that of the raw material." Nana brought up the projection interface. "The composition is mainly aluminum-titanium alloy, with a small amount of unknown stable isotopes mixed in, which may be due to the special smelting process inside the research station."

"Sounds high-tech," Chen Hao grinned, "but all I care about is how sturdy it is."

"Simulation tests show that it does not deform when subjected to 500 kilograms of pressure at minus 40 degrees Celsius."

“Okay, let’s use that.” He made the decision. “Make the connectors first, then modify the chassis.”

Nana got up and walked to the storage shelf, taking out a set of molds. Chen Hao then began cleaning the workbench, piling the old parts aside. The two worked together skillfully, one preparing materials and the other adjusting the equipment, without exchanging any more words.

Once the furnace temperature reached the critical point, Nana activated the blower. The metal slowly melted in the crucible, tiny bubbles appearing on the surface. She used a robotic arm to control the pouring spout, injecting the molten alloy into the mold.

"The first one is finished," she said.

Chen Hao leaned closer to take a look. It was a U-shaped connector, somewhat rough on the surface, but structurally intact. "Looks alright. Let it cool down and then I'll try installing it."

Over the next few hours, they fabricated the main beam components in sections. They adjusted the parameters with each pour to ensure accuracy. Midway through, the furnace went out once due to a gas leak at the fuel interface. Chen Hao tightened the screws, restarted the furnace, and his face was blackened by smoke.

"Your cooking skills are getting worse and worse," Nana said, glancing at him.

“I’m just being down-to-earth.” He wiped his face. “What do you robots know about real-world experience?”

By the time the first batch of parts was finished, it was already dawn. The two moved the finished product to the testing area and began assembly.

“The original skateboard was too wide, and it was easy to get stuck in snow when turning,” Chen Hao said while tightening screws. “I plan to change it to a double-track type, with a fine-tuning angle at the rear.”

"Which car model did you reference?" Nana asked.

"I don't know the name, but I remember seeing snowmobiles used for hauling goods on TV before." He paused for a moment, "Anyway, the principle is similar. If the wheels can be tilted a little, the steering becomes more flexible."

Nana didn't refute, but instead took out the blueprints and compared them. "It's feasible. But we need to add a linkage rod and a limit block."

“We have some ready-made.” Chen Hao pointed to a pile of scrap materials next to him. “The exoskeleton frame that we took off yesterday is perfect for use.”

They spent over two hours modifying the chassis. After the new structure was installed, the whole thing looked more compact. Chen Hao walked around the sled twice and nodded in satisfaction.

"Next step, counterweight."

He designed a recess at the bottom of the cargo hold that could be temporarily filled with sand or water bags. "The front is light and the back is heavy, so it's not easy to tip over," he said. "If you're hauling a lot of cargo, you can just add some more material at the back."

Nana scanned the center of gravity distribution model. "After optimization, the tilt angle is reduced by 12%, and the stability is significantly improved."

"Of course." Chen Hao patted her shoulder. "With the two of us working together, what problem can't we solve?"

No sooner had he finished speaking than a problem occurred during the braking system test. Even with the handbrake fully engaged, the skateboard only stopped halfway.

“Insufficient power transmission.” Nana inspected the mechanism. “The original design relied on a foot-operated lever, but now it’s been changed to a manual cable, and the travel is insufficient.”

“Then let’s lengthen it.” Chen Hao disassembled the outer casing and found that the steel cable was too short. “We need to replace it.”

He pulled out some recycled power tools, removed the motor housing, and pulled out the drive cable inside. "This is long enough and can bear weight."

After reassembling, they pushed the sled outside to test the brakes. The ground was covered with a thin layer of ice, making it slippery to step on.

During the first test, Chen Hao pulled the handle hard, and the sled jerked violently, the front of it lifted up, and it almost tipped over.

"I braked too hard!" He released his grip, panting. "I need to loosen it up a bit."

Nana recorded the feedback data and adjusted the spring tension. The second test showed much smoother deceleration.

“Pass,” she said.

“That’s not enough.” Chen Hao stared at the bottom of the skateboard. “We need to add anti-skid chains.”

He found several pieces of thick steel cable, cut them into smaller sections, and fixed them to the edge of the skateboard with rivets. Although the workmanship was rough, the serrated protrusions were quite obvious.

"The grip on the ice is expected to improve by 60 percent," Nana assessed.

"Then let's try again."

They pushed the sled for 300 meters, braking suddenly three times along the way, without slipping.

"It's done." Chen Hao grinned. "This time I'm really not afraid of it flipping over."

It was afternoon when they returned to the workshop. The two did a final check, repaired a few welds, and applied an insulating coating to prevent low-temperature cracking.

As night deepened, the temperature plummeted. Nana used an infrared scanner to scan the entire vehicle and discovered a tiny crack in a weld seam.

“Stress concentration due to cold contraction,” she said.

"Just fix it." Chen Hao heated the welding torch and lay on the ground to work. Twenty minutes later, the crack disappeared, and he added a triangular support plate. "This is stable now."

The final step is a self-test of the entire machine. Nana connects to the control system and tests each functional module one by one.

Lights, brakes, steering, load balance... all passed.

"Airworthiness status confirmed," she said.

Chen Hao stood beside the sled and reached out to touch the scorching hot brake axle. He smiled, turned around, and tossed his backpack onto it.

"We'll leave first thing tomorrow morning."

Nana packed up her tools and closed the last storage box. The sled was parked in the loading and unloading area, its brand-new frame and snow chains illuminated by the lights, like a battle chariot ready for battle.

The wind outside stopped, and the snow stopped falling.

Chen Hao looked up at the sky; the stars were very bright.

Just as he was about to speak, he suddenly heard a soft thud from the sled.

It looks like metal is contracting.

He looked down and noticed that the connecting pin of the right rear slide rail trembled slightly.