Droppers have to be activated by a pulse of redstone to move an item into the next container. Hoppers will run automatically unless they have a redstone current going into it to shut it off. If you are moving items to the side or downward, it is far more efficient to use hoppers. but hoppers cannot move items upward where droppers can at least do this, so you have to use some sort of repeated pulsing mechanism to move the items up in a dropper tower.
Also... it is really easy to mix up the dispencer with the dropper, so make sure you are using the right device for this project.
Also... it is really easy to mix up the dispencer with the dropper, so make sure you are using the right device for this project.