Fastest response time with USB controlled servo

[Symantic]

My plan is this, i have the general idea in my mind what i want to do. I need to take an item like a pen and be able to point it any direction via computer.

The programming isn't the issue, i need to make this thing move as fast as possible. maby the weight of 3 ounces in total.

my first idea is to use a controller like the one on this page.
http://www.trossenrobotics.com/parallax-usb-servo-controller.aspx?feed=Froogle

then from here the servo controller would take input from the computer via usb, one motor would be my X axis and the other motor would be my Y axis, thats a sinch to program (especially with that board, looks easy to use)

im thinking my X axis servo would be a little larger to hold the weight of the stand (mount the stand directly on top of the servo motor) and then my y axis would go to a gear mounted directly to the pen object that would allow it to look up and down.

My goals are this
-make the responce time from the computer to the actual movement of the robot as quickly as possible.
-make the robot be able to keep turning in a circle (i have ideas on spring contacts that will allow me to send signals to the y controller while keeping the x axis turning no matter what)
-keep the consistancy of the position as exact as possible (as exact as i can get it)
meaning if i say x axis point +94degrees then if i tell it to go back there it needs to be in the same spot everytime.
 

Any help would be greatly appreciated.

-Henry "Sym" E.

[sonictj]

I would suggest using a stepper motor.  You can achieve both higher speeds than a servo and greater accuracy. Look into the st micro l297/l298. They together make an excellent stepper motor driver.  I have 2 on my robot for scanning sensors.  The only issue I see is that steppers are heavier than servos.  You would also want to pick a stepper with high resolution say 200 steps / rev.

[Admin]

'fast as possible' is subjective. You need to give us a quantitative value

Also, speed and accuracy are inverse values of each other. You can have super fast servos with accuracy a 100 degrees off!

Look into digital servos, they are faster and more accurate than hobby servos. But you need to figure out what you need, and read datasheets until you find something that matches