Question

Some of the new yo-yos have a special "clutch" system that, when the yo-yo slows down, makes the yo-yo come up by itself. How does this work?

Answer

The idea behind these new 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 the yo-yo comes 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 get good at sleeping a normal yo-yo 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 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!

It turns out that the new yo-yos are patented. If you want to learn about the details of the clutch, see this page for the patent. You can click here to visit one of the manufacturers of these yo-yos.

The centrifugal clutch in a yo-yo works in an opposite way to normal 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 chainsaw the chain starts moving as the engine's speed gets revved above the idle speed. You can see that in a "normal" centrifugal clutch, the clutch engages when the RPMs rise. In a yo-yo the clutch disengages when the RPMs rise. In either case it's the same phenomena - when something spins weights move outward.

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