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Poi are tethered weights used for dancing, which often have battery powered lights in them.

Clearly work is being done on the poi, first to accelerate them, then to keep them going at constant velocity despite air resistance. I'm curious whether it would be possible to power the lights via the work done by the dancer rather than needing to replace/recharge the batteries externally. Obviously the amount of energy the dancer needs to exert would go up as well, regardless of the method.

One idea that clearly wouldn't be sufficient would be to use current induced by the Earth's magnetic field. Are there any methods that might produce more power? It'd be cleanest if these methods would work while the poi were spun at constant velocity, but methods relying on variations in velocity or tension in the tether would also be interesting.

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    $\begingroup$ Search term: self-winding watch $\endgroup$
    – rob
    Jul 5, 2023 at 3:30

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In principle it might be possible. But it is probably not particularly practical. There is work being done to spin up the poi (and to keep it spinning), but it is not easily extractable.

  1. As a poi spins the tension in the string varies between the poi at the top and the bottom of the circular loop. The string could be anchored to a piezoelectric transducer, at its connection to the poi. That would likely generate enough electricity to operate an LED. On the down side, it wont work if the poi is rotated in a horizontal circle (unless you add the complexity of some sort of energy storege system).
  2. Alternately, you could add a fin for directional stability and a little wind-turbine to generate electricity. That could definately generate enough electricity to operate a few LEDs. On the downside it might look more like a little model helicopter at the end of the poi.

Neither of these options is likely to be particuarly practical - whereas a number of flashing LED's could easily be powered and controlled for several hours from a single button-battery and a tiny circuit board. That would only add a couple of grams to the poi and I am sure you could easily find a suitable circuit in any hobby electroniucs magazine.

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