https://www.youtube.com/watch?v=u_3qLa5GMoY&feature=youtu.be
Simple and compact setup that uses a 9g servo to push/pull a shaft in a linear fashion. Shaft was scavenged from an old CD player, though you can drill whatever size you want to suit your needs. Holes intended for self-screwing 4-40 screws.
Uses a Pololu Micro Maestro servo controller and a Popsicle stick to secure the micro-servo.
Find more info and discover some of my other projects at my blog: http://teamctrlaltdelete.weebly.com/
Questions about assembly? Just leave a comment.