Great Illusion...

The four ramps in this device actually slope down toward the center, so the balls are really just rolling downhill, powered by gravity.  The illusion is created by making the ramps non-rectangular in a very specific way.  From one particular perspective, this tricks your brain into thinking that the ramps slope upward toward the center – thus creating the illusion of balls rolling uphill.  You can see this for yourself as the demonstrator rotates the entire assembly – you'll suddenly see it as it really is, with all four ramps sloping down toward the center...