RE: [CAD_CAM_EDM_DRO] Re: Stepper Motor Driver

I'll chip in my 2c worth.
Many people start off thinking they will build the cheapest cnc machine ever
and that all this fussing about ballscrews, bipolar chopper drives,
acceleration curves etc.. is either a pretentious waste of money or a means
of generating speeds that they don't require. I know I started this way. 7
Versions of stepper drives and at least 2 rebuilds of the drive screws
later, I feel I am now closer to the "truth". Making a machine you are happy
with on a hobby budget just isn't possible. Yes you can experience the
thrill of generating motion, but important issues like backlash,
repeatability and wear will end your project.
On a small project budget of say US$500 you could make a TINY machine that
would last, maybe, and I'm talking 50um and 1m/min here.
The technology to make a useful cnc machine is reasonably advanced (in terms
of power and precision) and, by hobby standards, is expensive.
I bet there are a lot more wood framed nc routers sitting in the junk box at
the moment than there are cutting swarf.

The thing is, don't be discouraged by this! Set yourself some and ask for
help (which you have done, congratulations on that. If only I...), when you
have a good idea what you want to do, cost it, again with help. Then start
work.

Now, to avoid this looking like a condescending newsgroup post:

Having stuffed up a small mill and completed a lathe conversion I'm building
a tiny router/mill http://www.rcmodels.net/cnc/hobby/cnc.html

I've had the laser cutting done.
I have built a 3 axis drive board with some additional opto isolated io
based on he allegro 3977 chip.
I built a second for a buddy who is scratch building an NC pcb drill (he
felt he could do it better and cheaper, but that's for another post :-)..

I also have some other uni and bipolar drive circuits for higher currents.

I'm happy to share any of this.

PK


-----Original Message-----
From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of turbulatordude
Sent: Sunday, 2 October 2005 8:06 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re: Stepper Motor Driver

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
> Blue wrote:
>
> >Hi,
> >
> >I was going to use this driver with 50oz motors of 1 amp using a power
> >supply of about 20 volts. The machine would be quite small for
> >drilling/routing circuit boards.
> >
> >
> Well, you would need to add resistors. A 1 Amp/winding motor would not
> have a 20 Ohm winding resistance, or it would go up in flames.
> So, you would need to add 2 resistors of about 19 Ohms (assuming the
> motor drops about 1 V at 1 A) at 360 W. Each motor/drive combination
> would need 720 W from the power supply, so a 3-axis system would draw
> over 2 KW!
>
> >Speed is not really an issue but I wouldn't want o wait all day for
it to
> >finish a job. I thiught it was a cheap alternative to proper drivers.
> >
> >
> Well, you will get your 50 Oz-In when standing still, but at 60 RPM, you
> might have only 5 usable Oz-In, because of R/L and resonance problems.
> The performance of such a drive is going to be so abysmally below a
> good bipolar microstepping drive that it is almost impossible for
someone
> who has not seen it with their own eyes to believe.
>
> The IRFZ44 transistors are not properly driven to saturation by a 5 V
> power supply, which is what the logic supply voltage is. The logic
signals
> are not opto-coupled, which may cause noise problems in a multi-axis
> system. There is no provision to control the inductive energy when one
> of the transistors is turned off, which may cause the transistors to be
> damaged by this energy.
>
> Yes, it is a cheap alternative. They left out the last 35 years of
> development
> in stepper drives.
>
> Jon


All this may be true, but for a cheap PCB driller type machine where
high performance is not needed, these would move the axes around.

Dave





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