Elon Musk is bringing together man and machine to make the Model 3, in a process that’s led to the Tesla CEO spending nights sleeping at the factory to bring production up to speed. YouTuber Marques Brownlee — also known as “MKBHD” — uploaded a video Monday of an August 15 tour of the Fremont factory, giving fans a glimpse of the inner workings of Tesla’s factory.

While Musk initially described his new Gigafactory as the “machine that builds the machine,” he admitted in April that “excessive automation” slowed Model 3 production in the early stages after the July 2017 start. Musk found that humans are better at some jobs, like wiring on the Model X, which has to poke through holes and weave through, a task that’s “super difficult for a robot…a pro human can do this super well, and it’s hard for robots to do that” as there’s “so much complexity and variation” with wire threading.

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The scaling back on machines requires a lot more people. Employees had to move from 5,000 to 10,000 in one location alone, using initiatives like rapid transit and ride-sharing to get people to work. “Actually doing things manually can actually be more efficient,” because using robots requires advanced technicians always on call for 24-hour operations. Musk notes that two days ago, he had to fly back from Germany at 2 a.m. to solve a sudden robotics issue.

Musk hasn’t pulled robots out of the equation entirely, but different machines pose different challenges. “This is one of my favorite dumb robots,” Musk said, following a simple magnetic stripe plus proximity sensors to traverse the factory “like a little train” that requires little programming. The giant robot arms, named after X-Men characters, require large amounts of programming and sensor wiring to enter the production line. A medium-sized robot can be accurate to 0.2-0.3mm, but like the giant arms, they too can fail without the correct setup. Musk announced a hackathon in May to smooth out the programming with complex bots.

Speed is still a key focus at the factory. The car coming out at the end moves less than one mile per hour for the S and X models that produce around 2,000 per week, but that figure is gradually approaching one mile per hour for the entirely separate Model 3 production lines that produce around 5,000 per week. Walking speed is three miles per hour, meaning the cars leave the factory relatively slow. Musk spent a lot of last year at the Gigafactory to fix battery module production, which involved fixing “a lot of real simple stuff times 1,000,” like the rotations per minute of a bolt driver, and reducing complexity like taking a turntable out of the equation that moves a car between one robot to another.

As for the cars at the end, the factory revealed key details about which cars people are buying. The most popular color is black, followed by white, but while black is only slightly more popular in the United States, in Europe black is far more popular.