Re: What makes a motor a servo? calculating power

Stepper motors are designed very differently than brushless DC or AC
motors. If you take one apart (get an old printer/floppy drive), they
have many small teeth formed into the main poles of the motor. When
the field switches between poles, the rotor jumps to the next tooth
position. The smaller the distance between the teeth, the more
commutation cycles required per turn. All motors no matter what the
design can only run at so high a commutation frequency before iron
losses and inductive effects start to hamper performance. Stepper
motors reach this frequency at a much lower rpm than servo motors.
This limits max power output greatly. Brushless motors on the other
hand can turn VERY fast. Some outstanding examples turn about
40,000rpm with a continous output of around 1.5KW and a peak over
3.0KW (4hp). These motors weigh less than one pound!! While they
won't be used for CNC anytime soon, it gives you an example of how
power dense a brushless system can be. Servo motors simply outperform
a stepper system in every way except price. My first cnc tabletop
router was stepper powered, in my quest for speed I tried to drive it
ever faster and faster. I managed a cheetah like 70ipm but found the
steppers very unreliable at this speed. Any little tiny gunk on the
rails would push the motors over the edge, and I would lose steps.
Right now I'm designing an AC servo driven router, and will be ashamed
if I can't manage 700ipm on my X-axis.

David Bloomfield

stepper motor tutorial ->
http://www.hsimotors.com/technical-data/theory.htm

some AWESOME brushless motors -> http://www.neumotors.com/neuproducts.asp