The best stepper driver??? was Re: Stepper questions

OK.. Well, some people design Ferraris and some people buy them.
Other people design Nissans and people buy them too. Both tool down
the freeway at 65 MPH and both get from A to B at 65 MPH at precisely
the same time.

But, for those times when you really NEED 200 MPH....

Mariss



--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo" <ballendo@...>
wrote:

>
> >In CCED, "Mariss Freimanis" <mariss92705@> wrote:
> >The two step motor phase windings don't share a common flux path
> >and thus don't interact. Proof: try using a 4-wire motor as a
> >transformer. Put a <snip of technical details, reposted below>
>
> Hello Mariss, CNC'ers,
>
> All true, and good to know.
>
> The laboratory I'm interested in is the one where we make parts;

the

> shop. The shop/work/hobby area of myself and our customers and
> potential customers.
>
> And in that shop, over many years I've used: unipolar linear,
> unipolar L/R, unipolar Bi-level, unipolar chopper, bipolar L/R, and
> bipolar chopper drives. From MANY mfrs.
>
> Nearly ALL of them have worked reliably, and ALL of them have made
> parts. Each HAS been worth the money spent.
>
> All have NOT made parts at the same rate, OR with the same ease to
> put into use. Some, we still use because "we've got them", but

won't

> be replacing with the same drive style in the future. Others we

will

> ikely buy again over time.
>
> So to replace long-term generalities with present specifics:
>
> We've got Gecko, Xylotex, PMDX, THS, EAS, HCNC, GeoM, and many
> others at work. (FWIW, I run each of these mfrs. drive nearly every
> day doing real work in a real shop. And others not listed here as
> well.)
>
> Gecko's are clearly the best, and their price refects that. They

are

> also overkill for MANY projects.
> I use them and appreciate their performance and features where the
> added price--and in my case the larger difficulty to wire up--since
> my GeoM drives are plug-n-play.
>
> Xylotex, THS, and PMDX all use the same chip; a bipolar chopper
> rated by its MFR. at 35VDC and 2-1/2A. (PMDX says their drive will
> handle 3A reliably and I trust Steve's ability, so I'll not

question

> his spec. I've also been running his drive with a 3A motor for a
> year without fail.)
>
> IMO/E all these drives are within a hairbreadth of each other
> performance wise. Note that Jeff at xylotex also makes/made a 7062
> based board; but it does not seem to be his focus. I suspect that

is

> because the surface mount A3977 based board is less "expensive" for
> him to produce in many ways. Or he just feels it is a better choice
> for his customers.
>
> IMO the early xylotex were not as robust in actual shop use, as the
> other two. There was also a noise problem in the step/dir inputs
> which Jeff to my knowledge has fully corrected in present boards.
> Saying they were not as robust may be an unfair assessment, since
> their popularity meant a larger sample and response was presented

in

> these groups where much of my NON-personal experience is gotten.
>
> But I still read more often about xylotex boards going bad than
> HobbyCNC boards, and I've blown one myself. (It WAS my fault, and I
> DID do something stupid. Reverse polarity on the 5v supply. But

I've

> done stupid things with other boards too, and they've survived.)
> Jeff pointed out in a discussion we had on another list that might
> be due to the higher voltage diodes in the unipolar chopper used in
> the HobbyCNC boards. And he's likely right.
>
> BUT...
>
> At the end of the day in MY "laboratory"; I don't really care what
> the "technical" reason is, the results are what I'm after. And in
> side-by-side testing, I simply got better results with the HobbyCNC
> board than I did with the Xylotex and other A3977 based boards.
>
> Our target--for this project--did not warrant higher costs and
> capability, so Gecko, Rutex, and others were left out of
> consideration.
>
> So when I set out to design a FULLY plug-and-play system for folks
> who DON'T want to need to know all about stepper drives and how and
> why they fail, and how one is more efficient, etc....
>
> I went with the chip used in the HobbyCNC board; a Sanken 7062M.
> A unipolar chopper, rated for 3amps at 44VDC; it has higher initial
> specs than the "competing" chips like the A3977, L298, L6208, etc.
>
> It is less expensive than the chips with higher ratings like the
> LMD18245 and L6203--and I only need one per axis, so my board can

be

> the same size as the xylotex 3 axis drive. It is less expensive in
> our quantities than the discrete components used to make a Gecko.
>
> The 7062 costs a bit more than the A3977, but based on all the
> above, I designed a 3 axis board and a 1 axis board using it, and
> put those into our geoM plug-n-play MCU. I designed the board to

use

> EITHER DIN 5pin OR screw terminal outputs; so those who wish to use
> specific cables to their motors are able to do so.
>
> The HobbyCNC board is very large, and its layout and IO
> handling/pinout is IMO non-standard and incomplete. Mounting
> inexpensive effective heatsinks is difficult because the screw
> terminals get in the way. (you can use large tall expensive
> heatsinks to get past this, again increasing overall size.) I don't
> think electronics in 2006 need to be any bigger than they need to
> be; I like economy and elegance.
> I DO understand that Dave is going after a kit market, so having a
> larger board makes things easier for HIS customers. The HCNC board
> is noisier than the A3977 based boards. You have to put it together
> yourself.
>
> Against this, the board works. People use it, and like the RESULTS
> they get with it.
>
> Now, MY goal for MY customers, is that they DON'T have to know
> ANYTHING about CNC electronics to USE their CNC machines. (Except
> not to unplug things under power!<G>)
>
> With THAT goal in mind, I created a small, integrated, expandable 3
> axis board using a unipolar chopper style drive. I've tested it

with

> the "typical" motors folks will want to use and with the

inexpensive

> and widely available cables so they don't have to do any wiring.
> Like the HobbyCNC board which was its predecessor, it works.
>
> I gave it an expansion connector to provide for updates and
> configuration changes that seem likely both as a person grows in
> their CNC experience, and also as the market itself changes over

the

> next few years.
>
> Then I created a box with expansion panels, and created a list of
> likely expansion products to fit those panels, including probes,

IO,

> and power control. Also potential 2nd paralell, serial, USB and
> Ethernet input/ output. (these expansion products will be added to
> GeoM offerings as they are tested and available.
>
> I gave this box a power supply which has been tested with the
> expected motors and uses and again, it works. I spent a LONG time
> trying to get the box size "right". It is far smaller than anything
> having remotely the capabilities (that I'm aware of).
>
> And then I did my best to price it all fairly.
>
> So while we can debate the relative merits of one style drive over
> another--and I DO enjoy such debates as longtime members here WELL
> know<G>--it is MY opinion that for MY customers (those who just

want

> to have a reliable and EASILY completed CNC machine) this new GeoM
> controller box will get them where they want to be.
>
> Ballendo
>
> P.S. And I've hedged my bet by designing our GeoM box in such a way
> that nearly any of those other drives/boards may be used, if that
> makes sense for YOUR needs...
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
> <mariss92705@> wrote:
> >
> > The two step motor phase windings don't share a common flux path
> and
> > thus don't interact. Proof: try using a 4-wire motor as a
> > transformer. Put a function generator on one winding
> (the "primary"),
> > a scope on the other winding (the "secondary"). You will see
> nothing
> > on the scope.
> >
> > ------------------------------
> >
> > Unipolar drives have some severe drawbacks in high performance
> > designs. It is because a single center-tapped winding DOES act as
> a
> > transformer and the consequences are all bad:
> >
> > 1) The center-tap goes to +V supply. When one end-wire is taken

to

> > GND by a transistor (the "on" one), the other end-wire goes to
> twice
> > the +V supply. This voltage is seen by the "off" transistor.
> >
> > Transistors in an 80V bipolar drive see 80V stresses, transistors
> in
> > an 80V unipolar drive see at least 160V stresses.
> >
> > 2) Inductive energy recovery. The "off" center-tap to end-wire
> > winding carries (L*I^2)/2 energy when turning off. There is no
> easy
> > means of returning it to the supply, so it must be dissipated
> > (wasted). Usually zener clamps do this dirty work.
> >
> > A bipolar drive easily returns this energy back to the power
> supply
> > for re-use.
> >
> > 3) Circuit topology. A high-performance (switching type) unipolar
> > drive requires 3 transistors and 3 power diodes per winding to
> > efficiently handle energy return. However the transistors still
> > see "twice supply voltage" stresses.
> >
> > At this point the unipolar drive requires 12 power devices vs. a
> > bipolar drive's 8, the unipolar drive transistors see twice the
> > voltage of those in a bipolar drive and 6 motor wire connections
> are
> > required vs. 4 for a bipolar drive. All that to get the same
> > performance as a bipolar drive.
> >
> > 4) Failure modes. A failed transistor in a high performance
> unipolar
> > drive cooks the motor. A failed transistor in a bipolar drive
> shorts
> > the supply, blows a fuse and spares the motor.
> >
> > Most designers ask "All that for what?" Then they discard the
> > unipolar drive topology and go for the bipolar one.
> >
> > --------------------
> >
> > If anyone is interested, I can try to dig up a high performance
> > unipolar drive power section design and post it. Something I
> designed
> > and we sold about 30 years ago. I may still have it around on

some

> > old 10MB hard-drive.:-)
> >
> > Mariss
>