Once you’ve made your Arduino (or other dev board) blink, the next step for many is to make some sort of moving robot. Hobby servos are the logical choice as they can be controlled without too much in the way of external hardware, but what if you want to create linear motion, not just rotation? Things here usually become a bit more complicated, but Potent Printables has a ready-made printable (naturally) solution. The device attaches to a continuous rotation servo with a couple of bolts and nuts, as well as epoxy.
The design is explained in the video below, including a demo at around 5:00 of both the micro and full-sized servo version of the rig. Linear travel is based only on timing, so if precision is needed, you’ll have to consider other options — or perhaps add some sort of encoder or linear travel sensor to the rack.
For simple movement, however, this looks like a great design, featuring only three downloadable 3D-printed components. For an idea of where to use it, you might check out Potent Printables’ mouse droid that we featured here. Not only does it scurry around, but uses this type of linear actuator is used to push a side hatch open, revealing a hidden marquee display inside.