Each roller spins on it's X-axis. You can see the box move forward on my animation. I added a old metal look to the rollers, so they seemed used. Let me know what you think. Please leave comments.
STL (Stereolithography, filesize: 3.38 MB), OBJ (OBJ, filesize: 3.4 MB), FBX (Autodesk FBX, filesize: 3.95 MB)