This is fan for you or your computer that runs off any avalable USB port. I reccomend it for beginners into electronics, right up to the pro's.
It is easy and fun, you can make in literally five minites!!!
REALLY FAST AND EASY!!!
Step 1: Parts and Stuff
1 3-9v motor with blades (out of mini fan) (pictured below (without blades)
1 USB cable (can be ANY of the three types shown below, as long as it has the same wire layout
Some (tiny amount) solder
Nescessary tools (wire stripper/cutter, soldering iron, tape)
Step 2: The Building
First, cut the cable at the non-male end( its usually square or smll). Then strip the USB cable and solder thee RED and BLACK wires to their respective contacts on the motor (experiment to see which way makes the prop will push the air FORWARD)
If you're adding a switch, you might need to solder some extra wire depending on where you want it to go, but I didnt 'cause its more practical to use the plug as a switch).
Then Isolate the ramaining wires, tape it up and you're ready to go!
Step 3: You're Done!!! YAY!!!
I did'nt bother isolating the other wires. bad choice. Now if you sxueeze the tape around the contacts herd enough, you have a speed setting cause its shorting out!! YAY!!!
This design is highly customisable. You can add s rigid bar along the wire to give it a flexible stand, or add other componants to it as welll if you wand to get really technical.
Since I used a 3-Volt motor, and the Computer's Output is 9 Volts, My motor goes spaz. If you did the same, I wouldnt reccomend leaving it on for too long for risk of blowing the motor/ power supply. Alternativley, add a resistor to suit you're needs.
As PKM said, you could add a variable resistor off a radio or something, and for all you safety freaks out there you could even soulder up a PCB with resistor, fuse and protection diode!
Look, i really dont care about my computer anywas, its a piece of 3-year-old custom sh1t. It has a single core CPU, 1GB of ram and absolutley no physics processing capabilities. I mean, I cant get Phun (physics sandbox) to run past 1 FPS. Im serious!!! My halo games dont run too bad on it though.