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

Thanks Dave,

thats brilliant news mate!, i have 4 x 1.4 amp motors so now i can do a
small lathe and maybe a grinder as well. Great news!. Now all i need is a
bigger workshop!

Nick

----- Original Message -----
From: "Dave Rigotti" <drigotti@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Sunday, May 09, 2004 5:13 PM
Subject: 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.
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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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