Re: [CAD_CAM_EDM_DRO] Re: Stepper vs. Servo

Mariss,

Thank you for your good post on stepper vs servo. I will add a comment in
the form of a question, since I my experience is so limited. In my two
years of working on a controller using a stepper driven BP machine as my
test bed, I learned that acceleration and deceleration are real touchy with
steppers. I have found that servos are much more forgiving in this area.
Is this your observation? Also, when making moves with a stepper wherein
the x and y axi are very close in frequency, but not exactly, such as when
one makes a move at 43 degrees, DEPENDING ON HOW the pulses are generated,
the steppers may have more difficulty in following an irregular pulse rate
if there is one. This would seem like it would be an issue with controls
which are windows based.

I do not know how many of the various low end controllers would
demonstrate this characteristic, so I don't know how much of an issue it is
for most users.

I know you are a hardware guy, but maybe it is worth commenting on. Lost
steps are a pain in the neck, and starting and stopping with appropriate
levels of acceleration and deceleration are also issues that I consider when
thinking of the servo /stepper question.

Anyone, please feel free to correct me, which I hope you do if I am off
track.

Thanks for all of your valuable input,

Tom Eldredge

----- Original Message -----
From: <mariss92705@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Saturday, June 23, 2001 2:06 AM
Subject: [CAD_CAM_EDM_DRO] Re: Stepper vs. Servo


> Doug,
>
> Good evening! The main reason for picking a servo over a stepper is
> power. If what you are doing can't be satisfied with a triple stack
> 34 step motor then it is time to look at a servo.
>
> Servos have a lot of drawbacks compared to steppers much in the same
> way a Ferarri has drawbacks compared to a Chevy.
>
> Servos develop their power at high RPMs with modest torque compared
> to steppers which have high torque at very low speeds.
>
> Steppers are "plug and play" while servos require tuning to make them
> happy and behave.
>
> What you get for your trouble of reduction gearing, encoder matching
> and set-up tuning is 3 to 7 times the power delivered to your machine
> when compared to steppers.
>
> If you require 7 times more speed, or 7 times more thrust or "push"
> than what you are getting with steppers and you are willing to put up
> with engineering a system rather than going with what "feels right",
> you may be a candidate.
>
> Continuing the Ferarri vs. Chevy analogy, performance comes at a
> price. Either will get you from here to there, except one will do it
> far more quickly than the other. The price you pay for that
> performance is care in design and careful matching the motor to the
> load.
>
> Mariss
>
>
>
> --- In CAD_CAM_EDM_DRO@y..., dougwalker13@y... wrote:
> > Anyone build a gantry flame cutter?
> >
> > How do you deal with arcs and corners?
> >
> > Do you use constant feeds or varying feeds?
> >
> > I'm building a large gantry flame cutter. The work envelope is
> approx.
> > 65"x65".I've tried 5A camtronics drives and achieved 1000ipm rapids
> > with 150oz/in nema 34 motors. Feeded moves below 100ipm become very
> > cogy, and create excessive vibration. Tried gecko g201, and got
> > 1000ipm rapids and very smooth feeded moves down to 10ipm.
> >
> > I've got dozens of various nema 23,34 motors from 50oz/in to
> 450oz/in.
> > Assuming I settle on an approprite sized motor, and can assume that
> > lost steps will not be a problem.
> >
> > What would be the advantage of using servos and gecko 320/340s?
> >
> > Doug
>
>
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