I am satisfied that she can move alone shelf which does not move even when pushed. I also thought that the truck would be easy to come off, but cheaper than asking for a person. However, it is necessary to pay sufficient attention to the movement of heavy objects.
Since it can only move in one direction, it is difficult to change according to the direction, changing each time. To make it move in any direction, make a hard ball, etc. Develop manufacturer's new products. You can always sell.