Notice that the Hercules's large rubber wheels do not touch the edge of the step. The Hercules lands very gently on the step as it goes down. The lifting cams on the Hercules automatically lift the large rubber wheels up and over the edge. On the way back up the step they also lift the wheels up over the edge and set the wheels down exactly in the same place as they were when it went down the other direction. Notice how the Hercules lifts the load up and over the edge, never actually landing on the edge. Whereas with a normal non-powered handtruck the large rubber wheels would roll all the way to the edge of the step. This is why you never hear of a Hercules Stairclimbing machine breaking the edge of a step off, because it never puts weight on the edge of a step.