November 3, 2015 - No Comments!

Helping Tretorn reinvent the tennis ball (again)

Oakwood was asked to help Tretorn reconnect with their tennis fans. Tretorn is a brand with a lot of heritage and practically invented the tennis balls of today. Thus, we decided that the project should be around the iconic ball. A familiar item to any player (or anyone that has ever heard about tennis), the perfect message carrier.

In order to reconnect with the fans we had to make it personal. So we created the Tretorn Portrait Project and let the tennis fans create their own signature balls printed by a robot on Tretorn tennis balls.

This took place in our signature ball factory at the ATP and WTA tour in Båstad. During the week in Båstad Serena Williams, Marc Jacobs and 1300 others got their hands on a signature Tretorn Portrait tennisball.

Curious to know more about the tech behind this?

Round and hairy, tennis balls are complicated


We knew what we were getting ourselves into: printing on tennis balls is a complicated task. When you add the requirements that all prints should be unique, the printer isn't allowed to require much maintenance, and that the printing should be fast and fun to look at, things get hairy.

The first challenge was finding a way to print on round surfaces. Luckily, in our previous R&D experiments, we had played the with quirky “EggBot”, a printer that lets you print on eggs (yeah, you read that right). We knew that, with some work, it was possible to use that mechanism to print on a “normal” round object too. The Eggbot producers did not agree, stating on their official wiki:

“No matter what you do, EggBot will never produce good results on a tennis ball. Golf balls are okay, though.”

But those words only fueled our creativity and made us move forward.

So, in order to make it work, we had to modify a few parts of the printer and 3D print a few custom parts. About ten iterations later, and the testing of dozens of pens, we finally got something that was both easy to use, and gave stable results.

Detail of one of the custom parts we had to 3D for the Eggbot.

Machine readable images

The second big challenge was finding a way to process the photos for optimal printing. We took the pictures in a photo booth with an iPad. The iPad ran an app we designed to separate faces from the green background. It calibrated the contrast and converted it to B&W. Then it forwarded the image to another computer, that did the heavy lifting.

We figured we could get fairly high quality prints if we decomposed the image into several thousands teensy tiny little dots, that could be executed by the robots. But that technique had a prohibitively long print time (~20 minutes in our first tests) so we had to get back to the drawing board. We ended up creating our own C++ software (written with OpenFrameworks) that encoded the image into a combination of dots, straight lines and wiggles. They were fast enough for the machines to plot and still look visually pleasing. We managed to bring the print time down to ~2 minutes! This made the printing fun to look at, which in turn meant more shares in social media.

How our custom software looks like.

The orchestration

Once we got all the critical parts working it was time to orchestrate it together. We wanted our fictitious user guide to have only one instruction: “Press this button to turn it ON/OFF”.

All the parts of the system were connected via a local wireless network. As soon as the iPad took a picture, it sent it to the central computer which did the initial processing. Inturn, the computer sent a preview of how the ball would look to the iPad. The user could now confirm the print or take a new photo. If the print was confirmed, the central computer did the final processing, and sent it to the “printer manager”, a tool that queues the printers and decides which one is free.

At any point the operator (a person that mainly made sure everyone got their ball, since we pulled quite a crowd) could cancel or reprint portraits by connecting their cell phone to the network, and loading a web app into their browser.

In the end it all disappears

We knew we had done our job right when no one (outside of the team) had the faintest idea of how complicated things were behind the scenes. After all, we love technology, but it is only a medium to express ideas. What really matters is that everyone had a smile on their face while waiting for their portraits to get ready. And that Tretorn got some simple and honest brand exposure with their fans.

Published by: vincent in Cases, Tech
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