Mason Landon Smith

I started with a simple idea. I wanted to build a table that would wirelessly charge a smartphone, anywhere on its surface. Little did I know, I'd still be working on a new iteration today.

Before you keep reading, take a minute and brainstorm a couple of ways to go about solving this problem. Here are the two most viable options that I came up with:

A: Cover the entire tabletop with overlapping wireless charging coils. That way, no matter where you place your phone, there will always be a coil directly underneath it.

B: Use a single wireless charging coil and build a system that is capable of moving it around the entire table. So regardless of where you place your phone a coil will find its way under it.

Both of these options are daunting for separate reasons. ‘A’ is simple but unrealistic. The number of coils needed and the energy required to power them adds up quick. On top of that, this solution doesn’t scale well. If the tabletop is twice the size, it requires twice the number of coils. ‘B‘ has a lot of unanswered questions. How does the coil move? How does it know where to move? How does it tell a phone apart from a coffee cup? If it only has one coil, how can it charge more than one phone at a time?

As you probably guessed I went with option 'B‘. So I started working my way down that list of unanswered questions:

How will the coil move? I used stepper motors on a 2 axis gantry

How will it know where to the move? I built a translucent table top and mounted a camera underneath it. The camera was connected to a raspberry pi running my custom code that located and sorted silhouettes on the tabletop. That code then drove the motorized gantry to the exact position of the phone.

How will it tell a phone apart from a coffee cup? The code has a shape sorting component to it. First it counts the vertices of the shape. Then it checks the aspect ratio. If the shape matches the proper dimensions, then the code deems it a smartphone. In the future I’m planning to add a method of monitoring the coils power consumption to confirm alignment and eliminate false detections. That way it won’t try and charge older smartphones which cannot be charged wirelessly.

How will it charge more than one phone at a time? By using a polar gantry instead of a cartesian gantry. Multiple arms can be used in the same table without interfering with each other but they cannot be charged on the same radius.

The first video below is my original wireless charging table in action. After designing and building it, however, I wanted to continue iterating and improving the system. Since then, I have started working on a second table. The other video shows the progress I'm currently making on a second iteration of the system.

After designing and building my first wireless charging table I immediately wanted to continue iterating and improving the system. Since then, I have started working on a second table, which includes several major changes:

• Developing a system of ‘electric rails’ which supply power to the motors and coils. By switching to rails, I was able to eliminate the need for moving wires.

• Switching to a hollow shaft stepper motor that actuates linearly on a stationary lead screw. This change saves space by positioning the motor directly underneath the charging coil.

• Switching to a simple motorized wheel after discovering that polar gantries are extremely difficult to center if they rely on an ‘internal gear’ to control rotation.