The Cadencex Is the Bicycle Dynamo to Beat

I find it hard to believe this works well in real life situations.

The mechanics of that idea (driving a smaller wheel from the rotation of a bicycle wheel, without the usb charging and capacitors) is old (https://en.wikipedia.org/wiki/Bottle_dynamo)

It also is fairly unreliable in wet weather or when bicycle wheels aren’t perfect circles or bent a bit.

Because of that, it is being phased out on newer bicycles. Hub dynamos are popular in higher price segments, battery-powered lights in lower ones.

I don’t see why rolling over the wheel rim instead of over part of the tire would make this more reliable. I would guess it would be less reliable because of the tight tolerances to keep the dynamo lined up with the relatively small wheel rim and because of the smoother surface of the rim, compared to the tire.

When it works, it likely will be more efficient and less noisy, though. It might work well enough for those who keep their bikes in perfect working order.