I was testing this about a week ago, but finally published it to the public. Taking all the same little electronics from the JuicedLink DIY slider project (continuous servo, servo driver, and battery case) the little Pico Flex dolly is moving on it's own. The speed is variable and with the size of the pulley. It can go really slow, but what you see is the fastest setting it will go. A piece of scrap acrylic plastic and double sided tape was all that was used to mount it temporarily while I try to figure out the cheapest and best way to drive this thing.
A rubber band pulley system didn't do so well. The band would stretch and when there was enough tension built up, it would snap back causing a jerking motion. The direct drive was the simplest way to turn the Pico wheels and was much more consistent. Using this technique could apply to all existing Pico Flex Dollies without replacing any existing parts. The servo is extremely strong and since the Pico moves with little effort, it can move quite a bit of weight.
Another Clever Pico Flex Dolly Modification - Motorized + Lasers
YouTube Member dim3m has motorized the Pico Flex, and has also added lasers for an easy way to identify the rotating axis. This is a common practice used in those high end three wheel skater type dollies. By aligning the axles with the lasers, the cross path will be the center of rotation. This is where you need to focus your camera. Right now the lasers are just temporarily being held on with Friction arms as a proof of concept. [Thanks dim3m] You can find pen lasers fairly cheap these days in just about any store, but if you're lazy they can be found online for about $1.49 (click here)
Mini Pen Laser KeyChains