At 22 metres tall and more than 20 years old, the Energy Machine is one of the Science Museum's most impressive and oldest attractions.
Generations of visitors have been awed by the sights and sounds of the complex device, but the museum's recent Muse Fest offered a rare glimpse into the inner workings of the world's largest kinematical, or "rolling ball", sculpture.
One of the museum's signature exhibits, it was built by engineering firm Ride and Show as an educational tool to teach about energy conversion.
Combined, the different sections of the track measure more than 1,600 metres, with different paths for 30 bright orange balls to roll along.
The balls gain potential energy as they are mechanically lifted, before this is converted to kinetic energy when they begin rolling, plus sound energy from hitting drums and gongs.
The museum's senior technical officer, Wong Chi-kin, is in charge of maintaining the various exhibits.
He is proud of the Energy Machine and talks excitedly about the work that goes into keeping it running.
This involves "routine maintenance every two weeks which takes about a day," he says.
"This means inspection, lubrication, ball changing and tightening up bolts and screws. There's a major overhaul once a year in September, which takes about five days."
Parts that are damaged when the balls collide may need to be replaced as well.
Wong adds: "A good exhibit can last a very long time with proper maintenance, and we see no signs of needing to retire the machine."
The noise created by the balls striking drums and xylophones may seem to be the most exciting bit, but Wong disagrees.
"I'm most interested in the electronic controls," he says, introducing the "brain" of the exhibit: a vending machine-sized computer with blinking lights, much like the inventions in old sci-fi movies.
"This Programmable Logic Controller is an industrial computer. The same kind used in factories and assembly lines."
Moving on to a desk scattered with machine parts, he says: "design and craftsmanship is the second most important concern after the computer."
"The whole machine is really a masterpiece of mechanical engineering."
He is responsible for its constant improvement. "Safety is one of our priorities," he says, standing under the machine as balls fly along the tracks above. There's only a net between Wong and an errant ball.
"There have been accidents before with balls flying off or parts breaking. But generally we have less than one accident a year. And our last was two to three years ago. Safety first," he says.
Muse Fest is organised to raise public interest in the city's museums, and Wong wants to attract others to his profession.
"I've been here for around 20 years," he says. "Museums are not places just to show off old things, but the best things. Art, in a way. To choose what to exhibit requires a sense of aesthetics and creativity, as well as practical concerns like safety.
"It's a lively job, not a regular government job."
The Energy Machine runs at 11am, 1pm, 3pm and 5pm daily, except on Thursdays when the museum is closed