Update September 2013: What started as a hobby has turned into something pretty serious. We are readying the launch of an open-source cinematic motion-control rig. If you wanna stay up on the futue of cinematography "like" us at http://www.facebook.com/openmocoUPDATES TO FOLLOW
2 Sets of Roller Blades
(16 wheels/32 ball bearings) from Goodwill
www.flickr.com/photos/bradjustinen/5882721666/in/photostreamAluminum angleAll threadnuts/washersMeade motorized telescope armSome sort of metal rail
I usually move the dolly by hand but for time lapse or slow movement I use a parallax continuous rotation servo that winds fishing line through a pulley attached to the dolly and onto a small spindle. I control the servo via a Traxxas (for a remote control car) controller and receiver. The Traxxas controller has a potentiometer on it that allows speed control of the servo in both directions. An easier option would be a rotisserie motor - I found one at Goodwill but didn't wind up using it cause I wanted to go wireless.
Give credit where credit is due, this project is a remix of these two projects: DIY video & timelaps electrical dolly
http://vimeo.com/9179128 DIY Inexpensive Camera Slider