Re: DC motor controller

Thanks Mark,

I'm trying to follow along, but I've never seen a servo setup
run. I feel like I did 4 years ago when I got my first kit
from stepperworld with 80 oz motors. The vids I've seen show
them(servos) zipping around with real authority.

I am greatly appreciative of all this help and advice.

I've got some stuff ordered to get into "Trial & Error" phase
as soon as possible. I guess a great deal will become clear
when Hook-up time comes.

I'll refer back to these posts many times.

I usually build a machine 2-3 times before I'm satisfied with it,
so I'm not counting on getting it right the first time.
The main reason the machine's 80% MDF.

For anyone interested, I'm going with the treadmill motors &
cheap encoders from surpluscenter. Gecko G320's.
Mainly because something similar has worked for Les for years.
I need to run ANY servo to get an idea of what to expect.
I can't go wrong having these motors on hand.
The parts I need(for now) are basic geometric shapes from MDF.
I won't know what I want to improve til I see something running.
The Gecko's are akin to currency...If I can't use them somebody
else can.

I want to do this in a way that the next guy can learn from it too.

We're all very fortunate to have such helpful and informed people
from all around the world giving their input.

Thanks Mark,

John

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mark Vaughan" <mark@...> wrote:
>
> Les wrote >>. Higher CPR encoders make it easier for the drive to
> compensate.
>
>
>
> This is a very good point for diy'ers. Many diy'ers look at the
output speed
> of programs like mach3 together with acceptable accuracy/resolution to
> decide how many count they will select for their encoder. But
resolution and
> accuracy are not necessarily the same.
>
> Many modern servo controllers have a divider to allow you to set one
step
> input pulse to correspond to several encoder output pulses. This
allows you
> to use a hi count encoder so the servo drive has very good accuracy and
> several counts per step so it can see errors within each step and
keep those
> error small to much less than one step resolution. The divider then
lets you
> set the step resolution, and maintain speed with your step
resolution being
> pretty much your maintained accuracy even with a little over and
undershoot
> error. (cogging problems excluded in poor servo motors). Try selecting a
> pulse count resolution of at least 4 times your step resolution.
>
>
>
> Regs Mark
>
>
>
> _____
>
> From: CAD_CAM_EDM_DRO@yahoogroups.com
> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Leslie Newell
> Sent: 12 November 2006 09:29
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] Re: DC motor controller
>
>
>
> Hi John,
>
> The servo drive will have to work to reduce the effect of the cogging.
> Modern drives are pretty good and can mask most of it. On my mill, if I
> watch the pulleys very closely I can just see the motor speed varying
> slightly at certain feed rates. It appears to have no discernible
> effect on accuracy or surface finish so I don't worry about it. Higher
> CPR encoders make it easier for the drive to compensate.
>
> Les
>
> John Hansford wrote:
> > Hi Dave,Ron,
> >
> > Pictures...
> > http://www.flickr <http://www.flickr.com/photos/26361144@N00/>
> com/photos/26361144@N00/
> >
> > I took the CW to mean the nut would probably fly off if it ran
> > the other way. I opened it ...Nothing flew apart.
> >
> > What's the Bad news...How _BAD_ could they be as servos?
> >
> > I wouldn't have noticed the very slight cogging if I weren't
> > trying to find it.
> >
> >
> > John
> >
>
>
>
>
>
> [Non-text portions of this message have been removed]
>