Project+Wing+ +Still+02 960 A Project Wing drone lowers a package using a winch. Google

Google has been working to replace your mailman with flying robots — but now it looks like on-the-ground robots might play a role too.

Alphabet, which is Google's parent company, has been working on a drone delivery service known as "Project Wing" since 2012 — though it was only unveiled to the public in August 2014.

When Google-turned-Alphabet introduced the project to the world in a YouTube video, it showed off a five-foot single-wing drone that could hover thousands of feet in the air and gently lower packages to the ground using a winch. Pretty cool, eh?

But a new patent filed October 2014 and approved Tuesday, which was first spotted by Fast Company, shows these drones will also be working with on-the-ground "mobile delivery receptacles," or tiny robots on wheels that will carry the packages to a safe holding location.

Here's how it works: the ground robots will be notified of an upcoming delivery and will travel to a location to receive the package. The delivery receptacle will communicate with the drone by emitting what is known as infrared (IR) beacons, a compact board that is used in pairs that allows robots to locate each other.

Using this robotic communication system, the drone will eventually lower the package down to the robot. The delivery robot will then transport the package to a secure location, "such as into a garage," the patent reads.

Google robot delivery A sketch of Google's on-the-ground delivery robot. United States Patent and Trademark Office

Alphabet plans on releasing its drone delivery service to the public in 2017, but the company isn't the only one working on using drones and on-the-ground robots for delivery.

Amazon is also working on a drone delivery service as part of its Amazon Prime Air, though there's no word yet on when the system will be released to the public.

And the co-founders of Skype are building an autonomous robot that can deliver up to 20 pounds of groceries in under half an hour. That project, called Starship, will begin trials in the UK at some point this year.

Disclosure: Jeff Bezos is an investor in Business Insider through his personal investment company Bezos Expeditions.