Here is another redneck, cheap, noisy, wobbly, thrown together machine, but it works. It was too big of a board on the video, she was struggling. The linear should have many applications in small Robotics, RC or shutting a small vent door in your chicken coop on a cold night by Arduino board and temp sensor. This Linear uses the DF Robot SER0037 Continuous Rotation Micro Servo (Jameco 2213448, $8.95) and 10-24 All Threaded Rod from hardware store. The servo gear attaches to servo with the small cross servo arm and screws that comes with servo. A continuous rotation servo is programmed by time and speed of servo, not servo rotation degree. More suited for push button type use or micro switch shut off when it gets to its end point. Uses 10-24 All Threaded Rod with a couple 10-24 Nuts pushed into the sides of spool. The spool spins the Machine screw nuts on the rod and moves the gear cases. Rod end should be anchored from turning, but it will push or pull from either cases or rod end. Using 10-24 all thread give a travel of .0625" per servo rotation. But you can have the rod as long as you want! If you need more power, I am sure 10-32 nuts and rod will work just as easy and would give you a .0375" rod travel per servo rotation. Much slower movement though. Nuts push against cylinder in cases and mush be filed down to fit how far you push nuts in spool. If you tighten cases and it quits moving file more. Will be doing a series of these with different size servos and rods to do bigger jobs, so stay tuned. The object is cheap easy and adjustable for about anything. Giving you ways to do things or move things. YouTube Video https://www.youtube.com/watch?v=P-A-YjTdik0