Remember that scene in Ocean’s 8 where Rihanna uses a trackball with a #9 billiard ball as the rolling element? Me neither, but Adam Haile does, and was, in fact, so inspired by the scene (or scenes) featuring this custom trackball that he had to have one himself. Unfortunately, the Kensington Expert shown in the movie nominally uses a 55mm trackball, while American pool balls measure in at 57.3mm, meaning that the chances of getting one of these to actually work correctly were slim to none. He also prefers thumb-type trackballs over that model’s center ball-style, meaning that another solution was needed.
While he could have started from scratch, a bit more research revealed that arcade trackballs commonly measure in at 2 ¼ inches, which just so happens to be the same diameter as the aforementioned billiard balls — if you divide by 25.4. Since it’s 80s tech, it’s incredibly hackable, with dual rotary encoders for X and Y movement. A Teensy 3.2 on a custom PCB took care of reading these encoders, and he added 5 LED-equipped pushbuttons as extra inputs.
The mouse was mechanically designed in Fusion 360, using a picture of his hand at rest as a template. This was overlaid it in the CAD model for proper spacing of the 9-ball and mouse buttons, and made for a rather massive apparatus — perfect for large hands. After a bit of 3D printing and a rather involved finishing procedure, Haile now has a beautiful mouse like none other, at least until someone else duplicates his design, files for which are available here on GitHub.