Re:305oz Steppers! More torque, Scotty!!!! (Shes' breaking up, I cannah hold'er)

It said that when I posted that, but it was probably in the
process of being updated at that time. You see where I
mentioned that in my next post...

I'm mostly interested in them for my Geckos.

I have a torroid that puts out 68VDC and with my 2.8V 3A
motors, that's getting close to the 25x rating mark.

I thought the general consensus was to stay closer to 20x
voltage rating...

Thanks Ballendo! it's all Very interesting to me :)

John

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo" <ballendo@...> wrote:
>
> Hello John,
>
> Are you sure that's not the spec on the 200 0z-in motors?
> (Those "should be" in that range; data sheet says 2.2mH)
>
> I'd not believe that for the 305's based on the other specs given.
> (My data sheet for an "equivalent"(see previous comments) motor
> shows 6.8mH for unipolar and bipolar-parallel; with a whopping 27.2
> for bipolar series.)
>
> However, if it WERE true... Then yes, it would "make them sound any
> better".
>
> Yes, prices for steppers mowadays ARE very good.
>
> Ballendo
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "John Hansford" <kz1927@>
> wrote:
> >
> > The Hobbycnc site says the inductance is 2.3mH...does
> > that make them sound any better?
> >
> > $45.00 *seems* like a good price...
> >
> > Thanks!
> > John
> >
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "ballendo" <ballendo@>
> wrote:
> > >
> > > >In CCED, "Dave Rigotti" <drigotti@> wrote:
> > > >HobbyCNC is pleased to announce that our CNC "Packages" are now
> > > >available with 305oz steppers! We also have them "ala carte"
> > >
> > > Hello,
> > >
> > > Another increase in stepper motor torque! Sounds great!
> > >
> > > (But there's a fly in the ointment, and nobody seems to be
> telling
> > > you about it. IMO it's time somebody did...)
> > >
> > > Let's review a couple things about stepper motors, and let's
> look at
> > > some published facts about motors likely to be VERY similar to
> the
> > > ones just announced, and the earlier/formerly "greatly increased
> > > performance" motors. (Quotes just above are for MY emphasis, NOT
> a
> > > direct quote from someone else.)
> > >
> > > I don't know for sure where Dave R gets his motors; but I do
> know
> > > that most of us selling motors with these specs are using the
> same
> > > motors... Made by the MS motor company in China, and many in the
> USA
> > > will source them from John at KelingINC.net
> > >
> > > So, let's review:
> > >
> > > Most of the time the Stepper torque published and mentioned is
> > > HOLDING torque. It's the biggest number, so it sounds the best
> for
> > > marketing. It's also the way steppers have been identified for
> > > decades. (Probably due to the previous sentence!<G>) BUT...
> > >
> > > It's important to realise... The motor will ONLY have this much
> > > torque when it is STOPPED. As soon as it starts to turn, the
> torque
> > > goes DOWN. FOR ALL stepper MOTORS. Regardless of drive type
> (bipolar
> > > vs. unipolar)
> > >
> > > How FAR down, and how FAST the torque drops, and along
> what "shape"
> > > or "Curve" depends upon some things about the motor, AND some
> things
> > > about the drive and power supply.
> > >
> > > Every motor is a generator when it turns. This is what causes
> the
> > > motor to lose torque as it goes faster. The important criteria
> for
> > > this are the motor power supply voltage, and the motor coil
> > > inductance. An additional factor is the drive type, unipolar vs.
> > > Bipolar.
> > >
> > > So let's look at the numbers for the Motors Keling sells as
> having
> > > the specs listed on Daves HCNC website. (Where the new 305
> oz.in.
> > > motors are listed as 6v,2.0A) Here are links to both 305's and
> the
> > > 200's as formerly sold by hobbyCNC (and still available from
> > > http://www.cncresource.com ):
> > >
> > > http://www.kelinginc.net/KL23H286-20-08B.pdf (2.15Nm, 305 oz.in.)
> > >
> > > http://www.kelinginc.net/KL23H276-30-8B.pdf (1.4 Nm, 200 oz.in.)
> > >
> > > Note: A Nm is a Newton-meter, which equates to about 141 oz.in.
> > >
> > > (Again I'll mention that I don't know exactly where Dave gets
> his
> > > motors; so these may not be the IDENTICAL motors he's selling.
> But
> > > I'd bet that if not, they're VERY close!)
> > >
> > > The first thing to notice is that the coil inductance for the
> 305 is
> > > over THREE TIMES as high (6.8mH) as for the 200 (2.2mH)...
> > >
> > > Note: mH is milliHenry's, a measure of inductance. Which is the
> > > motor coil's resistance to changing current direction.
> > >
> > > What this means (that matters to us in the DIY-CNC arena) is
> that
> > > the 305's are going to be a better generator of electricity than
> the
> > > 200's. Which is NOT good when you're looking for torque at high
> > > speed. Especially when you're limited in your ability to
> increase
> > > power supply voltage to compensate. More on that in a minute.
> > >
> > > So the motor turns and as it turns it generates a voltage. This
> > > voltage is called back EMF (ElectroMotive Force; which is the
> old
> > > name for voltage. And it's why Ohm's law is E=IR instead of
> V=IR).
> > > Back EMF basically subtracts from the power supply voltage.
> > > Which means that the motor will behave as if it is being powered
> by
> > > a supply voltage equal to the original power supply MINUS the
> back
> > > EMF.
> > >
> > > Keling doesn't show torque speed curves for all its motors and
> the
> > > ones it DOES show have the bipolar torque curve (because bipolar
> > > drive are more efficient, so that curve makes the motors LOOK
> > > better). Point is, we can't "see" the torque curve. But we CAN
> see
> > > that the back EMF will be higher than the 200's (due to the
> 6.8mH
> > > vs. 2.2mH that we CAN see on the spec sheets.)
> > >
> > > Translated into CNC-speak, the 305's will lose torque very
> quickly
> > > compared to the 200's as speed goes up. In fact, I wouldn't be
> > > surprised to find that the 200's outperform the 305's
> at "typical"
> > > speeds used in most DIY-CNC projects... (just a guess right now;
> > > I'll know for sure very soon!<G>)
> > >
> > > Let's get to the other factors in play here:
> > >
> > > Power supply voltage. If we can raise the power supply voltage,
> we
> > > can push the 305's to higher performance. And this is true for
> ANY
> > > stepper, up to a point of diminishing returns--and motor heating-
> -
> > > that Mariss of Gecko has empirically determined to be about 20-
> 25x
> > > motor nameplate voltage.
> > >
> > > Side Note: It is STILL BEST to always use the LOWEST power
> supply
> > > voltage which will give you the results you NEED. Sizing your PS
> to
> > > the max that the drive can handle "just cuz" is bad engineering.
> And
> > > that can lead to other unseen and unconsdered problems that
> you'll
> > > bat your head against later...
> > >
> > > The 305's have a 6 volt nameplate rating. The 200's are rated
> for
> > > 2.76V. (using ohms law to solve since this spec isn't on the
> linked
> > > sheet. Note that many of the "200's" imported into the USA were
> > > marked as having 1 ohm coils; in that case the motor volts will
> be
> > > 3V.)
> > >
> > > So as long as we use drives which have about double the voltage
> > > capability we may actually see the performance increase with the
> > > 305's. BUT...
> > >
> > > HobbyCNC drives are based on the Sanken SLA7062 (old revs) and
> > > SLA7068 (pro) driver chips. These chips have a MAX voltage
> rating of
> > > 44VDC. (We use these in our CNCResource drives as well; they're
> good
> > > chips.) Mariss has pointed out that a unipolar drive
> semiconductor
> > > has to be able to withstand DOUBLE the supply voltage. So these
> > > chips are probably using a 100v architecture, with the de-rating
> to
> > > 44V acounting for die variation and reliability improvement.
> > >
> > > HobbyCNC also recommends a 24VAC transformer secondary for the
> power
> > > supply. This will provide approximately 34VDC when rectified and
> > > filtered as suggested at the HCNC site. If you're going to buy
> these
> > > 305's, it would be a GOOD idea to increase your power supply
> voltage
> > > as much as you dare towards that 44VDC limit. If you do that the
> > > back EMF will be subtracted from this larger "number", and the
> > > torque will be carried out further along the torque-speed curve.
> > >
> > > Wait there's more...
> > >
> > > The 305's have a case thats almost 3-1/2 inches (88mm) long. The
> > > 200's are 3 inches (76mm). That in itself "may" not be too bad;
> see
> > > my P.S. following this post!<G> BUT...
> > >
> > > The ROTOR INSIDE the motor is ALSO longer. More mass. Put
> simply,
> > > slower. (all else being equal. Which I've pointed out IS the
> likely
> > > case where the power supply voltage is concerned due to limits
> of
> > > the driver chip used.) Another thing which doesn't get
> much "press"
> > > her in the build-it-yourself CNC groips is soemthing called
> > > mechanical impedance matching. Which can be thought of simply
> as:
> > > putting a v8 on a bicycle "might" give you problems! You've got
> to
> > > match the driven load to the driving motor (AND its defining
> > > parameters like drive type, power supply voltage and such!) to
> get
> > > anywhere near the deisred and expected performance.
> > >
> > > And there's another thing called detent torque that we shold
> > > mention. This is the effect of the reidual magnetic force acting
> on
> > > the mechanical shape of the rotor and stator stampings inside
> the
> > > motor. It is higher for the longer motors, and its effect comes
> > > right off the top of your torque expectation. It could be
> likened to
> > > a magnetic "friction" that must alwyas be overcome. Shorter
> motors
> > > usually have smaller detent torque.
> > >
> > > These tow factors are part of why you've read of drives being
> > > adjusted for larger motor types. Their mass and mechanics are
> > > different and this directly affect the results.
> > > You won't see this mentioned when only holding oz-in is being
> held
> > > up as THE decision maker!
> > >
> > > The point of all this is to say: Don't just look at the biggest
> > > number oz.in. quoted to decide your purchase!!! There's a LOT
> more
> > > to good CNC machine design than simply "bigger is better".
> > >
> > > And I'm taking the time to type this because when someone comes
> out
> > > and says only, "Bigger motors, get 'em here!" MY job gets
> harder.
> > >
> > > Because then I! have to explain all the things above to OUR
> > > CNCresource customer who's hearing "bigger, better, bigger,
> better"
> > > in his or her mind due to the one-sided push of "Performance"
> sales
> > > being done by others in the DIY-CNC arena...
> > >
> > > Now let's be fair and explain exactly WHERE the 305's are gonna
> be a
> > > good choice. Where you need LOW speed torque. Please keep in
> mind
> > > that this is low speed AT THE MOTOR. You can have a very high
> speed
> > > machine that has low motor speed. Belt and rack/pinion driven
> axes
> > > are good examples. The tradeoff there is step size/ machine
> > > resolution.
> > >
> > > Folks who've seen my writings over the years know that I often
> talk
> > > about the "balance" of DIY-CNC design. It's fun for me to see
> the
> > > design evolution of many "home builds" over on "the zone"; where
> > > after MANY iterations they finally empirically arrive at what a
> > > balanced design approach will give in the first or second
> > > pass...
> > >
> > > Finally, let's mention that the bipolar drives offered by
> Xylotex
> > > trade increased performance due to drive type for lower power
> supply
> > > capability and lower amps/coil specs, compared to HCNC and
> > > CNCresource.com driver boxes. FWIW, Xylotex are great drives,
> and
> > > Jeff supports them well.
> > > The net effect is that all three perform similarly with similar
> > > sized motors. (I've run all three in our lab and the empirical
> > > results support this statement. There ARE ways to skew the
> results
> > > in favor of the unipolar drives; which is why we're currently
> > > offering the SLA based unipolar drives at CNCresource. We'll be
> > > adding some bipolar drive options this summer.
> > >
> > > Anyways, hope this helps,
> > >
> > > Ballendo
> > >
> > > P.S. About those increasing motor lengths... thise of us in
> steppers
> > > used to expect that the motor body length would fall into
> roughly
> > > three lengths. We called these single, double and triple stack
> > > motors. This due to the fact that inside the rotor WAS divided
> into
> > > 1,2,or 3 distinct areas, or "stacks" of laminations. When the
> new
> > > range of Chinese motors came out; the old rules were blurred.
> > >
> > > Chinese mfrs. were "stretching" the "old" definition of what
> single
> > > stack and double stack meant... And pushing the holding torque
> > > number above all else...
> > > The first wave was sort of a stack and a half; then double
> stacks
> > > like the 200's. Now we're seeing triple stack motors being used
> in
> > > what were formerly "single stack" places. Because everybody's
> going
> > > after the "torque" by chasing the single HOLDING torque number,
> as
> > > explained above.
> > >
> > > Anyways, when I designed the Wood Duck CNC routers, we were
> using a
> > > 2-1/4" body length motor. Allowing for the "growth" I'd been
> seeing;
> > > I designed the machine to be capable of handling 2-3/4" bodied
> > > motors. Then the 3" motors hit the market. And everybody felt
> > > they "had to" have those (I've since re-designed to accomodate
> > > these, but I'm NOT going to keep adding just to "keep up with
> the
> > > Jones's"!<G> Especially when the "Jones's" is based on a
> partially
> > > explained truth... (We mfrs. are not operating in a vacuum, and
> we
> > > have to either educate or explain our competitors moves to our
> > > potential customers. Sometimes it's easier to just go with the
> flow.
> > > But there comes a time when the truth needs to be spoken.
> > >
> > > There's more to good CNC machine design than maximising oz-in in
> the
> > > motor spec! (FAR Better to maximise oz-in in the axis travels!)
> The
> > > two are NOT the same thing.
> > >
> >
>