So what you're saying Chung is that I need to measure the motor in action with the fan blade spinning, to measure the motor under load pressure, then I can use that current rating with Ohm's law to find the proper Ohm rated resistor?
I'm glad the 2.5volts thing has been figured out as optimal as far as the motor current is concerned. Still a little grey about the techno talk, but some good news is I found a local electronics store that sells boatloads of resistors, etc. So I'm going to bring in my modded fan and have them take a look at it with their gear to help me figure out the best resistor or diode to get.
I sure hope this fan actually lasts a long time, with all of this tinkering and research!
On a side note, I rigged a extra 90mm computer case fan with a spare usb cable. It's a fan rated 12v max and it's been working fine for the last 3 days. I'm assuming the reason it's working well if because it has a much higher voltage roof and despite it not spinning as fast as it does with 12 volts, it works pretty good.
Can I expect long term usb damage with this? It seem pretty harmless, like it's only taking whatever voltage it can get, in this case, 5v. Regardless, this is the nerdiest/coolest thing ever, I need to get a cheap metal fan grill for it, so it's a big safer. One wondering how much air flow a 120mm fan can get on 5v usb power?
My eyes will open for any gadgets that need 5v power, heehehe, fair game for a usb powered mod.