Re: [CAD_CAM_EDM_DRO] Stepper Motor vs Servo Motor

zone_369 wrote:

> I have three questions on this subject.
>
> What is the difference between the two motors?

Stepper motors have discrete positions that they step to, servo motors
can move to any position. For open-loop control, steppers are the only
way. For closed loop, steppers have a number of disadvantages. The
biggest is that misalignment of the stepper and encoder can make it
hard to reach certain positions, or cause endless hunting. Some stepper
drivers draw the most power at standstill. All stepper drivers draw a lot
of power at standstill, and provide motor torque that rapidly falls off as speed
increases. If you have a heavy machine to move, or want rapid acceleration
or high cutting forces, then you will find servo motors a better deal. Small
stepper systems are quite cheap, but when you get to large stepper systems,
they get VERY expensive. Servos can often be cheaper in the large sizes
(assuming you will buy surplus, not new.)

> Which would be better for a closed loop system?

My personal preference is always to servos for positioning systems, as in
mill/lathe/router machines.

> Where do I get them for a reasonable price?

There are a bunch of surplus sources. Herbach & Rademan, C&H Sales,
Surplus Center, Brigar, etc.

http://www.herbach.com/
http://www.aaaim.com/CandH/
Surplus Center -- Tel. 1-800-488-3407, Fax 402-474-5198.
http://brigarelectronics.com/

Jon