Chen Hao stared at the projection on the table. The dotted line connected the motor wreckage, steel pipes, gears, and the rammed earth machine casing, like an unfinished jigsaw puzzle. He rubbed his hands together. "Alright, since we have a way, let's not just sit here doing nothing."

Nana didn't speak, but the robotic arm had already started moving. She flipped the burnt-out motor over, aimed the optical lens at the internal copper wires, and shone a thin beam of light from her fingertip, beginning to inspect it segment by segment. "The thirty-seventh continuity test is complete. A section of coil that was not completely melted has been found and can be used as the core of the oscillation source."

"It still works?" Chen Hao leaned closer to take a look.

“The availability rate is 41 percent,” Nana said. “It’s not enough to drive the original equipment, but if the power output is reduced and the external structure is used to enhance vibration transmission, a simple tunneling function can be achieved.”

"I don't understand." Chen Hao waved his hand. "Just tell me if this thing can burrow underground."

"Yes," she said, "provided that the assembly is successful."

Carl stood up from the corner and walked to the table. "Shall we begin now?"

“Let’s divide the tasks first.” Nana brought up the 3D model. “Karl is responsible for repairing the steel pipe joints, which need to match the slots at the bottom of the ramming machine’s housing; Susan will deal with the broken blade and weld it into a front-end drill bit; Chen Hao will assist in fixing the main support frame.”

"Welding?" Susan frowned. "We don't have a welding machine."

“We’ll switch to high-temperature adhesive and metal straps,” Nana said. “The connection needs to be double-reinforced to prevent it from coming loose during vibration.”

"Are there enough materials?"

There are 37 screws, 21 of which have intact threads. There are four sections of steel pipe, and the longest section is used as the main shaft. The gear set retains the maximum gear ratio combination for torque transmission.

Chen Hao sighed, "It sounds like they're going to string scrap metal together like candied hawthorns."

“It’s essentially a functional restructuring,” Nana said. “It’s not just decoration.”

"Come on, you're talking like a screen protector installer is giving a philosophical talk." Chen Hao grabbed a steel pipe. "Let me try to see if I can connect it."

He inserted the steel pipe into the bottom of the rammed earth machine casing, shook it a couple of times, and said, "Too loose."

“It needs to be trimmed by hand.” Carl picked up a piece of angle grinder scraper. “I’ll scrape the inside diameter.”

"You really think you can cut something with that piece of junk?" Chen Hao asked as he squatted down.

“I used to work in a tractor factory,” Carl said as he worked. “I can even thin sheet metal, let alone this hose.”

Susan picked up the broken shovel blade and examined it. "The blade is crooked; it will deviate if used directly as a drill bit."

“Reshape it,” Nana said. “It can be corrected using a hammering method.”

"Use a hammer to hit it?"

"yes."

"What if it breaks?"

“The probability is less than six percent,” Nana said. “I recommend using rubber pads to cushion the impact.”

Susan found an old tire cover, laid it on the ground, placed the shovel blade on it, and picked up the hammer to strike. The first strike went astray, sending up a few sparks. The second strike hit the center, producing a dull thud. The third strike, and the blade was noticeably straighter.

"It's alright," she said, "but it's tiring."

Chen Hao held the steel pipe in place, waiting for Karl to finish so they could attach it to the casing. After twenty minutes of work, the two finally managed to insert the steel pipe into the casing, tighten it with screws, and then wrap it with two rounds of metal strapping.

"It looks like an elongated rolling pin." Chen Hao held it up and shook it.

“The power module is not yet connected,” Nana reminded. “The next step is to install the vibration source.”

She carefully removed the section of coil that was still conductive, placed it on the workbench, and then took out several thin wires to connect to the power module. "The voltage is twelve volts, and the current is limited to three and a half amperes to prevent it from burning out again."

"Is that all the electricity you have?" Chen Hao asked.

"This is the highest output currently," she said. "We can try connecting battery packs in parallel to improve the range later."

The coil was installed inside the housing and connected to the gear set's linkage shaft. Nana adjusted the angles several times to ensure there was no jamming in the transmission before closing the housing.

“The physical structure is complete,” she said. “It’s named the ‘Simple Vibration Tunneling Unit’.”

"The name is too long," Chen Hao said. "Why does it have to be such a long name?"

“It can be simplified,” Nana said. “I suggest the name: Groundhog No. 1.”

"A groundhog?" Chen Hao grinned. "That's pretty down-to-earth."

“Underground operation, small-scale equipment,” Nana said. “The analogy is reasonable.”

Susan handed over the repaired shovel blade. "The drill bit is ready."

“Install.” Nana took it, secured it to the front of the steel pipe with bolts, and checked the tightness again. “All components are in place. The first power-on test will be conducted in ten seconds.”

The room fell silent.

Nana pressed the switch.

The machine started with a whirring sound, the handle shook violently, and Chen Hao almost lost his grip, jerking back. "Holy crap! Is this thing going to reverse?"

He pressed the tool to the ground, the drill bit scraping a white mark on the concrete, a spark flashing. The noise instantly escalated, like an old refrigerator being violently shaken inside a mixer.

"Frequency imbalance!" Nana immediately cut off the power. "The vibration amplitude is too large, and the handle is resonating dangerously."

"I almost lost my hand." Chen Hao shook his numb hand. "Wouldn't it break if I did that again?"

"The problem lies in the circuit fluctuations." Nana checked the data. "The current at the drive end is unstable, causing uneven oscillations. A resistor module needs to be added for buffering."

"Where did the resistor come from?" Susan asked.

“We can use surface-mount components from scrapped circuit boards.” Nana disassembled an old mobile phone motherboard. “We extracted three that were connected in series; the resistance value is close to what we need.”

She started soldering, her movements precise. A few minutes later, the new module was connected to the circuit.

“The second test,” she said. “This time, we’ll reduce the starting power and gradually increase it.”

Power back on.

The machine started up quieter, the vibrations were still strong, but no longer erratic. Chen Hao gripped the handles with both hands, feeling a continuous high-frequency vibration emanating from his palms.

"It's safe," he said.

Nana aimed the drill bit at a mixed soil sample—a mixture of sand and gravel with broken rock—to simulate actual geological strata. Chen Hao pushed it forward.

The drill bit cut into the soil and slowly sank. Ten centimeters, twenty centimeters, thirty centimeters. The speed was not fast, but it did go in.

“It works.” Carl crouched down to examine it. “Although it’s slow, it can really penetrate hard soil.”

"The efficiency is about 1.2 meters per hour," Nana said. "Intermittent work is required when tunneling through rock strata to avoid overheating."

"Four and a half meters will only take three or four hours." Chen Hao released his grip. "It's not too outrageous."

“The problem is durability.” Susan touched the machine’s casing. “How long can this cobbled-together thing last?”

“It can operate continuously for 45 minutes under the current conditions,” Nana said. “It is recommended to stop it every 20 minutes to allow it to cool down. There is a simple ventilation channel inside, and its lifespan can be extended by replacing the gear set.”

"So, we have to dig and repair at the same time?" Chen Hao scratched his head.

“Normal maintenance is sufficient,” she said. “With enough spare parts, it can run continuously for more than six hours.”

"Turning junk into tools is quite a miracle," Susan said, patting the machine. "I thought I'd just have to go home and sleep tonight."

Carl held out his hand. "Let me test the feel of it."

He took the "Groundhog No. 1," weighed it in his hand, adjusted his grip, and said, "The center of gravity is a little forward, but I can still control it."

“I changed the grip angle,” Nana said, “to reduce torque loss.”

"You seem to know a lot about ergonomics," Chen Hao laughed. "You could make me a massage chair next time."

“We are currently short of materials,” Nana said. “In the priority ranking, excavation tasks take precedence over recreational equipment.”

"I knew you'd say that." Chen Hao stretched. "Alright, since it's working now, let's not delay it."

"Test complete." Nana turned off the power. "The tool is stable and capable of field operation."

"Shall we go dig now?" Carl asked.

"It's already dark." Chen Hao looked outside the door. "The LED strip lights are on, illuminating the area perfectly."

Susan stood up. "I'll go get the tool kit."

“I’ll go move the power cord too.” Carl put down the machine. “In case the power goes out, we need to connect the spare battery.”

The two walked out of the work shed.

Chen Hao stood there, staring at the thing on the table, pieced together from scrap metal. The steel pipes were bent, the casing was old, the drill bit was broken, and the wires were tangled. But it had actually drilled into the ground just now.

"Do you think it can last until the tunnel is finished?" he asked Nana.

“It’s impossible to predict precisely,” she said, “but based on the available data, the success rate for completing the 4.5-meter tunneling task is 73 percent.”

“The failure rate is much lower than in college.” Chen Hao laughed. “Let’s go, let’s test its true abilities.”

He bent down, picked up "Groundhog No. 1," and carried the power cord coil in one hand, walking towards the door.

Nana followed behind him, her eyelight steadily shining with a blue light.

The lights outside illuminated an open area where Susan and Carl had already set up their auxiliary equipment. Chen Hao placed the machine at the designated digging point and plugged it in.

He took a deep breath and pressed the start button.

The machine hummed as the drill bit pressed against the ground.

The soil began to loosen.