André Prager turns away from me for a moment, rummaging through a pile of stuff on the cart he has pulled into the small conference room. There are lots of cut-up pieces of cardboard, with a few bags of colorful plastic odds and ends mixed in.

“I think the most valuable things in this building are cardboard and tape,” he says. He shows me a rectangle of foam-core with a straw, a broken pen, and a few thumb tacks stuck to it.

It looks like junk, but because we’re at 100 Mayfield Avenue in Mountain View, California, the headquarters of X, Alphabet’s secretive division dedicated to cranking out new Googles, it’s actually anything but. The building is stuffed with cool gear: self-driving car hardware, an 80-foot flatbed scanner that inspects stratospheric balloons, a sprawling tool shop populated by hulking machines with names like Metabeam. But for Prager, this grown-up arts and crafts project represents years of work, and one of many steps on the way to a system that could make drone deliveries actually happen.

Mechanical engineer André Prager built numerous prototypes in his hunt for the perfect mechanism to drop packages from the sky. Damien Maloney

Prager is a mechanical engineer for Wing, the drone-delivery effort that, along with internet-beaming balloon scheme Loon, just “graduated” from X and is now a stand-alone company under the Alphabet umbrella. The engineers at Wing, which took shape in 2012, have had to deal with lot of complexities. They designed an H-shaped drone that has a range of 6 miles, can carry a 3-pound package, and tops out at 80 mph. They developed a traffic-management system that could keep the skies safe as they get more crowded with little flyers. And they spent a whole lot of time making a new kind of hook.

The importance of the hook dates to the early days of the project. One of the first decisions the Wing team made was that they didn’t want their delivery drones to land when dropping off packages. Vertical flight is a drain on power, and putting the drone on the ground means putting it within reach of curious (and destructive) children and animals.

LEARN MORE The WIRED Guide to Drones

But by the time Prager joined the team in 2016, they still didn’t have a workable idea of how to get the packages onto the ground. They couldn’t just drop them. Parachutes would soften the landing, but what good’s a drone-delivery service if your burrito ends up in your neighbor’s yard or a tree?

So the team decided they'd have the drone hover about 15 feet off the ground and lower its payload, sealed in a cardboard container, to the ground on a string. To start, they wrapped a piece of string around a bobbin and stuck it on the belly of the drone; a programmed motor would start the unspooling when the aircraft reached its destination, the way a yo-yo drops from your hand. But what seemed simple quickly proved a mess. Winding the things was a pain. You had to make one for each individual package. And then, the package would arrive on the customer’s doorstep trailing a long piece of string—hardly an elegant solution. “We’ve got to get rid of this bobbin, was the conclusion,” Prager says.