RE: [CAD_CAM_EDM_DRO] servo or stepper size selection

I agree that a servo system using Gecko G320's and my servo motors is
just about the same cost as an equivalent stepper motor system. I also
love the silky smooth performace of the servo system. A servo system is
a bit more tricky to set up because first you have to set the Gecko
current limit, gain and dampening, then you have to dink with the
software max speed, and acceleration but once you got it then you're
set. I have converted most of my machines servo's and the last one will
get them soon.
Dan

-----Original Message-----
From: William Scalione [mailto:wscalione@...]
Sent: Saturday, January 04, 2003 6:05 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] servo or stepper size selection


Jan,

I have to disagree with you here, I keep reading on this list how much
cheaper stepper systems are than servo systems, and how much easier they
are to set up, but I don't think that is necessarily true. Sure, if you
are going to go with a full analog system the servo system will be more,
but if you are going to use Gecko's or other step and direction type
drives. the price is about the same.

Drives - the gecko servo and stepper drives are about the same price,
maybe a few dollars difference

Motors - Just one example - Dan Mauch sells a 600 peak oz/in servo motor
with encoder for $159.00, and a 785 oz/in stepper for $170.00. At
anything more than a few hundred rpm's, that servo will have more torque
than that stepper. On ebay or other surplus sources servo motors are
usually much less than steppers

As far as complexity, a step and direction servo system requires about
the same amount of wires to hook the drive to the motor and computer.
About the only thing more complex is using good shielded cable for the
encoder wires, but you should be doing the same thing for the step and
direction wires on both the stepper system and servo system, so it's
nothing new.

Performance - I have used both and I would never go back to a stepper
system. No mid band instability or whatever it's called, just very
smooth motion all the way from a standstill to top rpm. No missed steps,
and most important, if the servo amp has not faulted, you can be 100%
sure that the axis is where it is supposed to be. On a stepper system,
there is always a doubt, that the motor has missed steps on that last
circular interpolation that you had the override set too high on.

I keep reading to buy the best you can afford when building your
machine, then in the next sentence, someone will suggest going with
steppers instead of servos. I guess I should be happy, as the $50.00
servo motors on ebay have less bidders.

What is the opinion of those on the list who have switched from steppers
to servos, as to price and performance comparasion.

Bill