Re: [CAD_CAM_EDM_DRO] Re: L297/L298

Hi Wayne,
You make some good points. I was looking at the L298 mainly because it's
cheap and abundant. The LMD18245 looks really swell but at over 6X the cost
(since you need 2) it changes the economics quite a bit. I've seriously
considered going to discreet MOSFETs but the gate drive requirements for the
high-voltage MOSFETs looks like a real pain in the keester. Sure would be
nice if you could get discreet high-voltage MOSFETs with built-in gate
drivers to accept logic-level control signals. Haven't been able to find
anything like that. Anyone seen such an animal?

I've been working on a controller for serial communications as well using a
PIC16C745, and have been able to generate rapid moves up to 50 KHz with
trapezoidal acceleration profiles. Better than I expected. Certainly not
adequate for high-speed servo drives with 1024-step encoders, but plenty
adequate for many hobby applications, especially for steppers. Anyway,
unless you're using a really coarse pitch lead screw or big gear reduction,
a 1024-step shaft encoder seems like major overkill to me. Most hobbyists
seem to be looking for bargains, and overkill is counter-productive in that
quest.
--
Phil Mattison
http://www.ohmikron.com/

----- Original Message -----
From: Wayne C. Gramlich <Wayne@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, August 04, 2006 10:28 AM
Subject: [CAD_CAM_EDM_DRO] Re: L297/L298


> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Phil Mattison"
> <mattison20@...> wrote:
> >
> > I've been experimenting with various designs for bipolar
> > stepper motor drivers and I'm curious if anyone has had a
> > similar experience. Is it just my perception or is the
> > L297/L298 combo a piece of junk? It seems no matter
> > how I configure it the thing just runs way hot if it
> > carries anything near its rated current.
>
> Phil:
>
> I'll give a somewhat contrarian point of view here.
>
> The L298 is a bi-polar device and consequently
> generates more heat in operation than its FET
> counterparts (e.g. A3977.) With a good heat sink,
> a fan and operated within specifications, L298's
> operate just fine.
>
> From a price point of view, they are still quite
> competitive with their FET IC counterparts. For
> example, the L298 can be purchased from Jameco
> for less than $3 quantity 1. A heat sink for
> the multiwatt15 package can be obtained from
> Mouser for about $1 (Mouser #: 532-655010B3400G ~$1).
> Of course, you also need some free wheel diodes like
> the 1N5822, but those are inexpensive as well.
>
> From a convenience point of view the FET IC's win
> hands down. If you are only building one, the FET's
> are the way to go. If you are thinking about building
> hundreds, it is not as easy to dismiss the L298.
>
> The L297 is at best a half step chip. These days
> a micro-step solution tends to be preferred. It
> is fairly easy to dump the L297 and replace it with
> a microcontroller. My most recent table top drive
> electronics are posted on-line at the following URL:
>
> <http://gramlich.net/projects/cnc/axis4/index.html>
>
> It works just fine. I make chips with my Sherline
> CNC conversion using the driver above. I'm still
> tweaking my total software toolset, but the basic
> microstepper stuff using the L298's works quite well.
> No, I can't step at 500kHz, but realistically I doubt
> that most table top machines need to run quite that
> fast. My driver won't win any IPM drag race derby's
> but it will make chips just fine.
>
> This is probably not be the consensus view on L298's.
>
> -Wayne
>
>
>
>
>
>
>
> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
> Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
> Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
> List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com, wanliker@...,
timg@...
> Moderator: pentam@... indigo_red@... davemucha@...
[Moderators]
> URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there, for OT
subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> bill
> List Mom
> List Owner
>
>
> Yahoo! Groups Links
>
>
>
>
>
>
>