The idea behind these yo-yos is to make it easier for the yo-yo to sleep. A "sleeping" yo-yo is a yo-yo that is spinning on the end of the string. You release the yo-yo, and when it gets to the end of the string it sits there spinning. By jerking the string you make the yo-yo come back. There are lots of tricks you can do while the yo-yo is sleeping, but sleeping is a hard skill to master. A normal yo-yo has a simple, polished shaft that connects the two halves of the yo-yo, and the string wraps around the shaft. It takes a good bit of practice to make a normal yo-yo sleep because the string has a tendency either to bind on the shaft or to never catch the shaft.
The new yo-yos use a centrifugal clutch to make it easy for the yo-yo to sleep. The string is attached to a spindle, and the spindle is free to spin on the axle. Inside one half of the yo-yo is the clutch. When the yo-yo is not spinning (or is spinning slowly), the clutch clamps onto the spindle and holds it. When the yo-yo is spinning fast enough, weights in the clutch are thrown outward and the spindle is free to spin on the shaft. As the yo-yo slows down, the clutch weights move inward again, grab the shaft and the yo-yo returns. The yo-yo automatically knows when to stop sleeping based on the speed it is spinning!
The centrifugal clutch in a yo-yo works in an opposite way to regular centrifugal clutches. Lots of things use centrifugal clutches to connect a gasoline engine to a drive shaft. Common examples include chain saws, go-carts, mopeds and some riding lawn mowers. The idea is simple -- there are weights in the clutch attached to the engine's output shaft. When you rev the engine past a certain rpm level, the weights in the clutch fly outward. Shoes attached to the weights rub against an outer cylinder and the clutch engages. In the case of a chain saw the chain starts moving as the engine's speed gets revved above the idle speed.
You can see that in a regular centrifugal clutch, the clutch engages when the rpms increase. In a yo-yo, the clutch disengages when the rpms increase. In either case, it's the same phenomenon -- spinning causes the weights to move outward.
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