Freddy’s career at the store has gotten off to a rocky start. Workers there said it has suffered nervous breakdowns, needed regular retraining sessions and taken weird detours from its programmed rounds.

Shoppers are not quite sure how to interact with Freddy, either. Evan Tanner, who works there, recalled the night he says a man fell asleep on top of the machine as it whirred obediently down a toy aisle.

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Walmart executives said they are skeptical that happened, because the Auto-C is designed to stop if someone interferes with its work. But Tanner insists Freddy dutifully stuck to the job at hand. “Someone had to pull [the sleeping man] off,” he said. Freddy “was going to swing toward groceries, just cleaning away.”

Over the past 50 years, Walmart has recast the fabric of American life, jostling mom-and-pop shops, reshaping small towns and transforming how millions work and shop.

But the superstore titan’s latest gamble is an entirely new kind of disruption — the biggest real-world experiment yet for how workers, customers and robots will interact.

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The nation’s largest private employer has unleashed an army of robots into more than 1,500 of its jumbo stores, with thousands of automated shelf-scanners, box-unloaders, artificial-intelligence cameras and other machines doing the jobs once left to human employees.

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The swarm is already remaking how the retailer’s more than 1 million U.S. “associates” go about their daily work. Given the chain’s ubiquity across the country, the local Walmart store also is likely to become the first place millions of Americans meet a real-life, working robot.

Walmart executives have promised the all-hours robot workhorses will let employees endure less drudgery and enjoy “more satisfying jobs,” while also ensuring shoppers see cleaner stores, fuller shelves and faster checkouts.

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But the rise of the machines has had an unexpected side effect: Their jobs, some workers said, have never felt more robotic. By incentivizing hyper-efficiency, the machines have deprived the employees of tasks they used to find enjoyable. Some also feel like their most important assignment now is to train and babysit their often inscrutable robot colleagues.

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Customers, too, have found coexisting with machines to be confusing, if not alarming. Some shoppers have been spooked, for example, by the Auto-S scanner, which stands six feet tall and quietly creeps down the aisles, searching for out-of-place items by sweeping shelves with a beam of light. Other shoppers, store workers said, have made a game of kicking the things.

Employees at a half-dozen newly automated Walmarts said the machines at times are helpful, even charming. Some talked about the robots’ personalities and said they had adorned them with employee name tags. But others also felt this new age of robotics had accelerated the pace of work and forced them to constantly respond to the machines’ nagging alerts. Some said it made them doubt the company valued their work.

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This awkward interplay of man vs. machine could become one of the defining tensions of the modern workplace as more stores, hotels, restaurants and other businesses roll in robots that could boost company reliability and trim labor costs.

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Many Walmart workers said they had long feared robots would one day take their jobs. But they had not expected this strange transition era in which they are working alongside machines that can be as brittle, clumsy and easily baffled by the messy realities of big-box retail as a human worker can be.

Walmart executives say that the machines are helpful companions that will allow workers to focus on more-creative, customer-facing goals and that early responses from workers have been “overwhelmingly positive.” In an announcement last month titled “#SquadGoals,” the company said it would be expanding its robot program and compared the machines to the Star Wars droid R2-D2 and the Transformer Optimus Prime. “Every hero needs a sidekick, and some of the best have been automated,” the company said.

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The robots also don’t complain, ask for raises, or require vacations and bathroom breaks. During a company earnings call in August, Walmart president and chief executive Doug McMillon said the machines were an important part of how the company, which has annual revenue of $500 billion, could trim waste and “operate with discipline.”

“We’re testing or scaling new automation efforts in several areas,” he said. “Our mind-set and specific plans and actions around cost management are vital.”

The scale of the effort is impressive. The Fast Unloader machines automatically scan and sort freight as it is tossed off shipping trucks. Auto-S camera robots roll past shelves to scan which products are mislabeled or out of stock. Giant orange obelisks, called automated pickup towers, spit out goods for online shoppers like 16-foot-tall vending machines. Scurrying little Alphabots bring items to workers for packing. Auto-C robot Zambonis come out at night to buff the floors.

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One Walmart Neighborhood Market in Levittown, N.Y., has 100 servers, 10 cooling towers, 400 graphics-processing cards and 150,000 feet of cables in service of a complicated artificial-intelligence system designed to assess the store in real time. Cameras and weight sensors automatically detect when the shopping-cart pen is empty and the bananas are overripe.

But the technology can only do so much. When the AI senses a problem, it sends an alert to the handheld devices most Walmart workers are expected to carry, saying it is time to corral the carts or replenish the produce. The store’s roughly 100 human associates are the ones who do the physical work.

That has added a layer of discomfort to a job some workers said already could feel demeaning. Quitting or getting fired, some joked, is like getting “promoted to customer.” Now they find themselves in the uneasy position of not only training their possible replacements but also tending to them every time something goes wrong.

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The self-driving floor scrubbers, for instance, must be manually driven until they learn the store’s layout — and when the aisles are shifted around, as is common during seasonal displays and remodels, the machines must be retrained.

Technical glitches, surprise breakdowns and human resentment are commonplace. Some workers said they have cursed the robots out using their employee-given nicknames, such as “Emma,” “Bender” and “Fran.”

The human customers have to be trained, too. Walmart workers said they have seen people following the robots around, recording them, talking to them, slapping their emergency-stop buttons, jumping in their way suddenly — and, yes, assaulting them with kicks and shoves.

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The inventory-scanning robot is well-traveled: Its kind has captured more than 3 billion images across 24,000 miles of Walmart shelving, all at speeds of less than a half-mile per hour. But to customers, it remains a stranger. “Customers freak out when they see him,” said Dreama Lovett, who works at a supercenter in Jacksonville, Fla. “They’ve not seen anything like him before.”

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Other customers find their time with the robots to be unsatisfying, including older shoppers for whom a trip to the store is as much about human interaction as anything else. “A lot of them will say, ‘I didn’t come here to talk to a machine,’ ” said a worker at a Walmart in Dunedin, Fla., who spoke on the condition of anonymity because he didn’t want it to affect his job. “ ‘I came here to shop and have someone help me with my groceries.’ ”

Martin Hitch, the chief business officer of Bossa Nova Robotics, which makes Walmart’s inventory-scanning robots, said the company has spent years teaching its machines to be as human-friendly as possible. But there’s no agreed-upon etiquette for how robots and people should communicate.

Engineers did not, for instance, want the robot to silently skulk up and scare anyone — but how exactly should it announce itself? They tested a wide range of noises, from Road Runner-style “beep-beeps” to the honks of reversing forklifts before settling on a pleasant yet insistent chirp they mixed from a clip of birdsong.

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“The last thing you want it to do is talk,” Hitch said. “Because if you talk, people think they can talk back.”

Signals that seemed obvious to human testers have failed spectacularly when applied to the real world. The company put turn signals on a test robot, Hitch said, but it just confused people, because no one expected to see blinker lights while shopping for Cheerios.

Walmart said last month that it has reduced its worker turnover to the lowest level in five years and that more than 40,000 U.S. workers are in roles that did not exist two years ago. Most of the company’s U.S. workers make an average of about $14.26 an hour, company figures show.

But some said the automated tedium is getting to them. The robots have taken away some simple pleasures, such as walking the store, and pigeonholed them into some smaller, mind-numbing tasks. Self-checkout aisles, for instance, have replaced some cashiers and shifted much of the work to customers. But workers still have to stand by to guide confused shoppers, fix glitches and soothe the machine when it sounds the alert that there is an unexpected item in the bagging area.

Michael Webb, an economist at Stanford University who researches labor markets and AI, said it is no coincidence that the machines are first arriving en masse in big-box stores.

Those companies depend on volume — jumbo stores, lots of sales — so the burden of investing in robots can more quickly balance out. Higher-priced stores, he said, are also less likely to shift to robots. “The human service is this thing you’ve got to pay extra for now,” he said.

So what is the harm in working with a robo-sidekick that is helpful sometimes and a headache otherwise? In March, Boston University and MIT economists Pascual Restrepo and Daron Acemoglu argued that many of today’s automation efforts were not designed to boost productivity but to replace it, by swapping out humans for cheaper machines. That could make workers’ lives worse, they said, “if these new technologies are not great but just ‘so-so’ ” — good enough to be adopted but not that much more productive than the people they pushed out.

For Tanner, the employee at the Marietta supercenter, the rise of automation has made major changes to how he works. Formerly a department manager in the toys section, he now says he has to pick up the slack of a hugely trimmed staff: After the Fast Unloader was brought in, he said, the store cut the number of workers it had unloading trucks and saddled him with many more hours of putting away freight.