Hello, I made a scale horizontal axis wind turbine that I would like to connect to my phone to charge it. I am trying to decide which motor to buy. Here is my plan and question: Plan: The wind turbine uses a 12 volt dc motor so that when the wind makes the motor shaft rotate there is a potential difference of 12 volts in the output. I will connect the red, positive, wire to a 7805 ic voltage regulator to bring down the voltage to 5 volts (so that my phone doesn't short) and then connect the output wires to a USB charger cable that i plug the phone into. Question: There are several 12 volt dc motors I could use, with RPM ratings (with no load) from 100 RPM to the many thousands of RPM. What should I use and what is the difference (electrically, obviously the mechanical difference is the RPM). My guess is it works something like this: If you have a 12V 100RPM dc motor and you spin the shaft yourself at 50 RPM then the motor wont produce the full 12 volts (maybe around 6?), and if you spin the shaft at 100 rpm yourself then the motor will produce the full 12 volts. Whereas if you have a 12 volt 6,000 rpm dc motor then you would have to somehow manage to spin the shaft at 6,000 rpm in order for the motor to produce the full 12 volts. What is the relationship between the RPM you spin the shaft at and the voltage the motor generates--is it a linear relationship, logarithmic, etc?? Also does the 100 rpm 12V motor have a higher mechanical resistance to spinning the shaft than the 6,000 rpm 12V motor (not resistance in terms of V=IR, just resistance in terms of how hard it is to rotate the shaft at all)? Thank you for the help!