Took me a few tweaks but i made my machine work.
It's kinda simple, just 3 steps. pink wheels grab ball, blue wheels are just free casters that allow the whole contraption to be dragged around, and the yellow balls are a bridge pushing/clambering over device.
I would claim its simple and neat, but i would be lying. still, pretty nifty to watch.
Enjoy
http://fantasticcontraption.com/?designId=1164395