I had made this prototype before i realized so many people thought of the same thing but anyways i made a video of it and it works very well as long as the motor stays in both sides (see first video to understand).
PS sorry if its hard to see the camera work was pretty bad](http://www.youtube.com/watch?v=kwLx-_6-YSo&feature=youtu.be)
Nice! That looks like it works a lot better than I expected it to. Are you planning on holding the sacks in a ramp of some sort?
Well i have planned to put them on a flat surface and then when i get to the top have the ramp drop down