A fet (short for mosfet) is a semi conductor, it is only conductive in 1 direction. And only when commanded to be so.

A reversing brushed motor setup with mosfets is in essence an H-Bridge, meaning 4 fets (or a multiple of that) work together to control 1 channel.
For brushless you need 3 reversing channels to create the 3 fase alternating current these motors need. In theory you can hack a brushless speedo, and use all channels to control all 3 outgoing wires as 1. But that's theory. The BotBitz guys just programmed 1 channel away(and snipped off the wire) and use the 2 others as a classic H-bridge.

Magmotor, or ampflow as they are called now, come in all flavors. From -recently- rebranded Chinese scootermotors, to the Old powerhouse A40-300

http://www.robotmarketplace.com/prod...flow_main.html

And you can say the A series are expensive, de F and E series are a lot more affordable, but you get what you pay for.

I myself won't use e'm, modern technology gives us smaller, more economical alternatives.