Learn how to make a portable variable speed linear dolly / slider motor for shooting timelapse videos that can be used on any slider rig for about $55 AUD. For about $85 AUD you can have a deluxe version with two motors, one for timelapse and another for regular speed shots, USB power and a dedicated 12v battery and charger. Here's a little day trip I did to test the unit out vimeo.com/88152086. It rained the entire day, so it wasn't ideal, but you can see that it works!
NOTE: Want to do timelapse (or normal speed) panning shots with the same unit? Too easy! Flip the unit on its side and there should be a thread at the end of the drill chuck. Find a bolt that will go from the thread diameter of the outlet from the drill chuck to the 3/4" (or whatever it is) on your tripod head, screw your tripod head on, put on your camera and.... voila! Panning at timelpase speeds, and it'll spin indefinitely.
For the full parts list, including links, see askdesign.it/weblog/slider, noting that they are all on eBay so if that particular item has been taken down just search for it using the text description and you'll be able to find a live item. The slider used is an 80cm Konova K2. you'll need an intervalometer - I use Magic Lantern on my 6D, a hack which allows you to do intervalometer shots in-camera, but you can buy a unit off eBay for c. $30. Be sure to get one that can take an infinite number of photographs, many timeout at 99 (4 seconds of footage).
// Shooting Advice
1. Have fun!
2. Put a bit of tension on your sliders bearings and you'll get silky smooth motion, and use fishing line (or any string for that matter) that doesn't have any elasticity or give.