Rack and pinion devices are well-known mechanical devices that can turn rotary motion into linear motion. Usually, as the pinion gear turns one way, it slides in one direction; when turned the opposite way, it slides in the other direction.
Ronald Walters’ mechanism, however, as shown in his video below, only has to turn in one direction to slide back and forth. A full demonstration is seen around 6:45.
Walters had the idea for this device after seeing it demonstrated as an animation on the Internet. Though it seemed to work in theory, he wasn’t able to find one of these devices in real life.
To design the gears, he used the template generator from woodgears.ca, which required some trial and error to get everything lined up. That gear generator is only capable of printing a single rack, not a double rack setup that Walters used.
He did not use a CAD system or CNC, so everything had to be lined up and cut by hand. He used a scroll saw and a lathe for much of this process, but I thought the spindle sander used around 1:30, was a very interesting device, as I hadn’t seen one used before.
Also of note is that the small motor he used initially didn’t turn the pinion well, so he had to step up to the Roomba model. Though the pinion moves relatively fast, Walters notes that, “[The] mechanism operates effortlessly and smoothly and would operate more quietly with a slower turning drive motor (which I did not have). The original intended drive motor would have been much slower but it simply did not work…”
A very neat device. I could see something like this with a much slower motor being used for a time-lapse mechanism, or probably hundreds of other applications. Be sure to check out his YouTube channel for even more cool ideas!