[yash101]

Have you played with transistors before? A MOSFET, as mentioned earlier, is a very high powered transistor. Typically, though it is possible not to, you would have a filter capacitor attached. When the MOSFET is turned on, it will fill up the capacitor a little. If the MOSFET is on a greater portion of time, say, 1 second, the motor will get more power, and thus spin faster. However, if you have the MOSFET on for a lesser portion of the second, the motor would get a lower power and be slower. This will only work on brushed motors, and maybe those brushless motors with a built-in controller, like the ones in the computer you are using. If you are using brushless motors, like most quadcopter builders, you would need an ESC, a speed controller meant for brushless motors, much like the ones Andrew suggested. Also, why are you running 5 volts? What Battery technology are you using? If you are building a small flying machine, 3.7 volts (1s LiPo) may work. However, for most medium-large quadrotors, 7.4v (2s LiPo) or 11.1v (3s LiPo) would be optimal. If using Arduino for the controls, have a 5v regulator powering the control system, but have the motors/escs running off unregulated voltage. The ESCs that Andrew suggested have a built in UBEC (Universal Battery Eliminator Circuit), a wierd name for a buck voltage regulator, rated for 5v, 2 Amp. That should fall aplenty to power your Arduino and any other circuits. Some of these can severely reduce your cost, without reducing your quality. As a matter-of-fact, you may be able to get a better quality than those expensive ESCs from HobbyKing!

I would like to know what is your prefered power source, to help you get better information