RE: [CAD_CAM_EDM_DRO] Re: Stepper Motor Driver

lol - a topic ppl love to debate - mostly cuz it's
quite subjective - observe how the context has been
dropped...lol-
the question of 'goodness' ALways presupposes an anwer
to the questions: good to whom? and for what purpose?

what you are calling tiny is not necessarily what
someone else thinks of as tiny.
the taig mill and sherline - with tens of thousands of
happy users - can hold .001 or so, run forever on
screws & brass nuts (cheap replacement if/when needed)
and perform admirably for the uses to which they are
put. my backlash can be tightened to .001 noooo
problem.
for me - 1 meter a minute is about 10 times faster
than i'd ever dream of running it in metal - but You
are doing wood- and a router is barely getting started
at that speed...
so, for My uses, ball screws and microstepping ARE
wasteful expense. the parts that come off my machine
are within tolerance.
for Your purposes - you Do need faster and therefore
acceleration is an issue, etc...
Blue will be able to get excellent results cheaply
that suits the purpose he described using his motors
and cheap ass stepper controllers, brass nuts and
ready-thread. i see nothing in his requirements that
dictates a need for ballscrews or microstepping at
all.

see your 2cents and raise you a penny...lol

--- Paul Kelly <tech@...> wrote:

> 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
>
>
>
>
>
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