Serial PWM motor controller

[smartkid]

No way

You guys have no idea how hard I've searched for something like this. I actually did find this article: http://www.rentron.com/SerialServo.htm and I've been to Parallax (their $100+, 20MHz micro controller kit was what inspired me to do this project). But I was a bit confused as to exactly what it was about, I was knee-deep in servo-micro controller-PWM articles. A USB PWM controller is even better!

A question: Is there a major difference between USB and RS-232 serial?

To what RyanCahoon said, "you're probably going to want motors along the lines of what's used in FIRST [...] a lot of the low-current motor controllers would fizzle and die" Yes, the computer power supply uses 12V and 5V leads so the car battery we hope to use for power later on and the motors will all be 12V.

The design calls for 4 12V DC motors to move the bot in an omni wheel system which I've already had to make and program for a various school robotics competition coming up that I'm not allowed to give details about using Vex parts. hehe

The question that comes to mind though is do I really need to buy 4 $100+ speed controllers? I've worked on our teams FRC bot, what we're hoping to do is about 1.5 times smaller then that and shouldn't need quite as powerful motors.

Another small question that I'm sure someone here knows is, how long would you think a car battery would power the motherboard and the motors? It's an important thing to consider, I know many factors apply but an estimate would be appreciated.

And finally one last question, when working with Vex parts I noticed that the servos can work directly with the controller inputs (PWM output value of 0 set it all the way in one direction, PWM output of 255 spun it around the other way), do real servos work just like this? And do servos also need speed controllers (I assume yes and yes).

Thanks so much guys!
-Smartkid