RE: [CAD_CAM_EDM_DRO] EMC tuning question.

> -----Original Message-----
> From: elson [mailto:elson]On Behalf Of Jon Elson
> Sent: Friday, December 14, 2001 1:38 PM
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> Subject: Re: [CAD_CAM_EDM_DRO] EMC tuning question.
>
>
> jguenthe wrote:
>
> > I have a question about the relationship between DEFAULT_VELOCITY,
> > MAX_VELOCITY, DEFAULT_ACCELERATION and MAX_ACCELEATION. My system is
> > currently configured as follows:
> >
> > DEFAULT_VELOCITY = 0.0167
> > MAX_VELOCITY = 0.2000
> > DEFAULT_ACCELERATON = 5.0
> > MAX_ACCELERATION = 5.0
> >
> > On my Sherline 5400 mill with 20tpi lead screws this gives me reliable
> > rapids of 12ipm. I can increase MAX_VELOCITY up to 0.3000
> which should give
> > me about 18ipm. This seems to require changes to he
> ACCELERATION parameters
> > but I can't come up with the appropriate numbers to get
> reliable operation.
> > What is the proper relation for the ACCELERATION parameters to the
> > MAX_VELOCITY parameter?
>
> There is no standard numerical relationship. As your motors will be
> spinning faster, you may need to reduce the acceleration at the higher
> end. Since there is only one acceleration used throughout the move,
> you may have to reduce it for the whole move. velocity is in user units
> (either inches or mm) per second. acceleration is in units of
> user units/second^2. Acceleration of 5.0 sounds pretty high.

Acceleration of 5.0 is what the emc.ini and minis.ini files are set to
in the BDI release as it comes.

> It may be fine for a Sherline, however. Why do you think it requires
> changes? Are you losing steps? If so, then cut it way down, to
> 2.0 or less,
> and then if you want more acceleration, increase it in small amounts
> until you again get lost steps. Back it off a good measure to allow
> for machining loads, and you should have a good, reliable setting.
>
> If you are not losing steps, what are you worrying about?

I am losing steps when I set the MAX_VELOCITY to anything over 0.2000 and
since
I would like to have rapids of around 18 ipm this is a problem

> Anyway, assuming inches for the user unit, for a 5.0 acceleration but only
> .3 IPS velocity, the acceleration all happens in a small fraction
> of a second.
> If you set acceleration for .3, it would take one second to accelerate to
> full speed. At 5.0, it would take approximately .3/5.0 = 60 mS
> to accelerate
> to full speed. This is almost certain to require more acceleration than a
> small stepper can handle.
>

Ok, so it looks like the proper thing to do is set acceleration to a much
lower
number and work my way up to the setting that works best with my system.

Thanks for the info, things are much clearer now. There is so much to
learn,
so many projects and so little time!

John Guenther
'Ye Olde Pen Maker'
Sterling, Virginia

> Jon
>
>
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