What the set actually does
Lego's new Donkey Kong arcade cabinet is a working model of the 1981 Nintendo arcade game, built entirely from Lego bricks. The set includes a functional joystick that moves Jumpman (the character later renamed Mario) left and right within a limited range, and a jump button that lifts him up the way the original game does. A lever on the back releases barrels one at a time, and the set runs them through a mechanism that keeps the supply going indefinitely.
The set is the work of Carl Merriam, a designer with a track record of nostalgia-driven Lego sets. He has built some of the more ambitious fan-favorite projects of the last several years, including mechanical calculators and music boxes, and has assisted on multiple Lego Ideas sets. The Donkey Kong arcade is his most involved arcade design to date.
How the infinite barrels work
The mechanism is essentially a pump. A stack of 14 barrels runs up the side of the model, and each pull of the lever adds one barrel to the bottom of the stack while one falls out the top. The system holds 20 barrels in total, with 6 in motion at any given time, which is enough to keep the rolling section populated without a backlog.
The barrels themselves are the same barrels Lego originally released in 1989 for its first pirate sets, and Merriam said in an interview with The Verge that this was his favorite detail in the build. The hardest part of the engineering was getting the barrels to roll slowly enough to feel right without getting stuck. He said the trick was a combination of rolling them over steps, Lego studs, slopes, bows, and Lego Technic beams, which are slightly thinner than standard Lego bricks. The net effect is a controlled roll that captures the feel of the original arcade game.
Getting the barrel back to the top was the second engineering problem. Merriam's team tried several solutions, including a barrel-firing mechanism and worm gears, before landing on the simplest one: more barrels. The system forms a literal loop, which Merriam described as "barrels of fun."
Miyamoto's note, in Minifigure heads
The set has not yet been formally shown to Shigeru Miyamoto, the creator of Donkey Kong and Mario. Merriam said he has not met Miyamoto but has heard that he is "very happy with the execution of this set." Nintendo did provide one specific piece of feedback during the collaboration: the poison barrels had to be heavier than the regular ones. Lego solved that by adding Minifigure heads inside them, a small detail that gives the poison barrels a distinct weight and feel on the rolling track.
The Jumpman figure itself is a new, detachable Lego element, designed so players can move him with their fingers as well as through the joystick. Pauline, the damsel-in-distress from the original arcade game, is also part of the set, with her own design choices that Merriam discussed in the interview.
When it ships, and what it costs
The Lego Donkey Kong arcade cabinet set releases on August 1st. Lego has not announced pricing at the time of writing, which is unusual for a set of this size but consistent with how Lego has handled some of its more collectible adult-targeted releases. The set will be sold through Lego's own channels and through major retailers that carry the adult-oriented display line.
For anyone who grew up watching barrels roll down ramps in an arcade, the set is the kind of build that earns its shelf space. For Lego, it is a strong argument that the mechanical-design side of the adult display line can keep producing new ideas instead of just revisiting the same handful of vehicles and buildings.