This motor and gear drive is from a mainframe computer, probably the tape drive. The gear ratio is high, probably a dozen or more motor revs for one shaft revolution. But that just makes cranking it turn the motor faster. The motor says it’s 30VDC, and it uses magnets.
When I turn the makeshift crank once every 6 seconds, the motor puts out about 100 milliamps to the 3V. 1 watt, 10mm white LED, making it glow brightly. That’s about 300 milliwatts of power. It does a good job of lighting, but it’s difficult turning the crank and holding the motor with the other hand, not to mention doing something now that both of my hands are tied up.
What would be better if it was used like this Gravity Light. Quantsuff told me about this entrepreneur trying to develop a good version that will have a 25 pound (12 kG) weight hang from it, which supplies the power for a half hour. If the shaft had a bobbin on it, and I could wind a length of rope around this bobbin, then hang a weight from the end of the rope, the LED would light as the rope unwinds from the bobbin. But the distance the weight falls would determine the time the LED would light. I guess the bobbin could be mounted high in the air, so the distance would be great. Or else the diameter of the bobbin would have to be small, so that the distance per revolution would be small. Then the weight would have to be heavy.
One revolution every six seconds equals ten RPM. If the LED was to be lit for 30 minutes, that would be 300 revolutions. If each revolution released 4 inches of rope, then there would be 1 foot of rope for three revolutions, or 100 feet of rope unwound every thirty minutes. That’s a bit too long for hanging this device from a limb of a tree, for example. I can think of one easy way to halve the distance. I could get a pulley from the hardware store and hang the weight from the pulley. One end of the rope is connected to the bobbin of the generator and the other end is connected to the generator itself. Then as the weight and the pulley fall, the rope would travel twice the distance, or the total distance for a hundred feet of rope would be fifty feet of weight movement. Of course the weight would have to be at least twice as heavy, maybe more to compensate for friction losses.
This same principle could be used with more pulleys to get less weight movement for a hundred feet of rope travel. I don’t know how much losses there would be, but I would guess that the weight could be increased to compensate. The power to move the weight would have to be increased too. I’m guessing some kind of crank for the user to wind the weight back up to its highest point.
The whole point of this elaborate bobbin, rope and weight is to allow the user to store the energy so that the user can be using the energy later as electricity, thus separating the time of generation from the time of use. Another form of energy storage might be the same as these wind powered beach robots use in the Netherlands. These amazing robots use the wind to pump up air stored in plastic beverage bottles, which then power the robot later.