Re: [CAD_CAM_EDM_DRO] Uni vs. bipolar was Re: HobbyCNC NEW 3AMP Unipolar Chopper Driver Board!

Nick,
Actually you can run the chip at 1.4A without a problem, providing you
use a cooling fan rated at least 50CFM. I've run the little bugger at 2A
with lotsa cooling air for an hour without "smoke". NO I'm not endorsing
such an application. 1.4A should be fine even at 35VDC.

I'm looking forward to the tests also that Ballendo suggests. I have some 6
wire 3A steppers coming my way, so these will be the "ultimate" the board
will handle. It would be interesting to run the tests at 24VDC, 30VDC and
at 44VDC to see what each board can do at its full potential. Should
eliminate alot of "guessing"

Regards,
Dave Rigotti
HobbyCNC.com

----- Original Message -----
From: "Nick Ibbitson" <pulseweld@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, May 09, 2004 12:04 PM
Subject: Re: [CAD_CAM_EDM_DRO] Uni vs. bipolar was Re: HobbyCNC NEW 3AMP
Unipolar Chopper Driver Board!


> Hi Ballendo,
>
> i will watch with interest as i have a Xylotec drive as well ( not that it
> isnt doing a great job with bipolar motors anyway) but its always
> interesting.
>
> Nick
>
>
> Quick question for Dave Rigotti, i still have the Hobbycnc board all set
up
> and now have some 1.4amp unipolar motors, I know you quote 1.25amp
> continuous use and up to 1.5amp at start up but odo you think i could use
> these motors if i put a nice big high volume fan to run over the board to
> keep it cool in use?.
>
> Nick
> ----- Original Message -----
> From: "ballendo" <ballendo@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Sunday, May 09, 2004 11:27 AM
> Subject: [CAD_CAM_EDM_DRO] Uni vs. bipolar was Re: HobbyCNC NEW 3AMP
> Unipolar Chopper Driver Board!
>
>
> > Jess,
> >
> > With unipolar you have an extra wire (or two) from your driver to
> > your motor... Higher connector cost... more wires to flex and break...
> >
> > Unipolar drives shut down a coil by opening a switch (transistor).
> > There is nothing to DRIVE the current out of the coil, so it decays
> > relatively slowly. This works okay because as the other posted
> > answers have pointed out, we have a center tapped coil, and are only
> > using 1/2 of it at any given time. So while 1/2 is "winding" down--
> > pun intended<G> we're using other coils. For many uses of steppers,
> > by the time we get back to it the current in the coil we shut off has
> > decayed, and is ready to be turned on again.
> >
> > Bipolar drives are more "pushy". They do not simply turn the coil
> > off, but reverse its polarity. To do this they use more transistors,
> > (4 per coil, instead of the 2 used in unipolar drives) and since the
> > motor voltage is always present(except during current control, but
> > that's another subject), the electrons are "marched", rather
> > than "walking" at their own pace...
> >
> > Torque in a motor is a result of copper area, and amperage. For a
> > given amps and copper area, the torque will be identical, whether the
> > drive is a unipolar OR a bipolar. BUT...
> >
> > Because the Bipolar "marches" the electrons through the coils, and
> > the unipolar "lets 'em walk"; the bipolar can switch the direction in
> > a given coil faster. However, the unipolar doesn't NEED to switch
> > direction in a coil, because in effect it uses a "different" coil...
> >
> > So we're back to the difference first mentioned above; a couple less
> > wires from the motor to the driver. There are cases where walking or
> > marching is the better choice, when ALL factors are considered.
> >
> > Now let's add two more truths:
> > The better bipolar drives ARE better than the better unipolar drives
> > where high speed torque is concerned. But not by nearly as much as
> > some would have you believe, or for the reasons often given.
> >
> > The second thing is that a bipolar drive allows you to use a given
> > unipolar motor(6 or 8 wires) at a lower amperage with the same TORQUE
> > at high speeds, WHEN you are limited by the driver amperage
> > capability.
> >
> > So you can take a 3volt, 4 amp motor and run it with a 2 amp bipolar
> > drive by using the whole coil. (Ignoring the center tap that you HAVE
> > TO USE with unipolar) This can let you use bigger motors with smaller
> > drives. The downside is that you won't have the same speed capability
> > because inductance is 4 times as high as the 1/2 coil value.
> > Sometimes if you have to use a certain motor and/or a certain drive,
> > it can be useful.
> >
> > Hope this helps,
> >
> > Ballendo
> >
> > P.S. When I get my HobbyCNC uni-chopper board, it's gonna be
> > interesting to compare it to my xylotex... using the Same motors,
> > same volts, same amps... And THEN optomising motors for each drive
> > type and re-running the tests...
> >
> > (Geckos can't be included in the comparison due to their added
> > features which make them more capable for reasons beyond the uni- vs.
> > bi- differences.) But the A3977 vs. the SLA7062M should be a
> > fair "race", as long as current and voltage are considered.
> >
> >
> > >In CAD_CAM_EDM_DRO@yahoogroups.com, <jess@p...> wrote:
> > >Could someone who knows explain -
> > >
> > >What are the advantages and disadvantages of unipolar and bipolar
> > >stepper motors. Or does anyone have a link to where this is
> > >explained?
> > >
> > > Jess Perez
> > >
> >
> >
> >
> >
> >
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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
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> 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........
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