Re: What makes a motor a servo? calculating power

--- In CAD_CAM_EDM_DRO@yahoogroups.com, bobmcknight@c... wrote:
>
> So MAXNC by putting an encoder on a stepping motor
> has a pretty neat system?
>
> bob mcknight
>
>
>
>
>
> On 11 May 2005 at 4:11, Mariss Freimanis wrote:
>
> I guess my point was missed entirely. My fault, let my try again.
>
> Servo motor:
>
> 1) Torque is independent of speed. If you have 60 in-oz of torque,
> you have 60 in-oz at 6 RPM or at 6,000 RPM.
>
> 2) If you need 600 in-oz, you have to have a 10:1 reduction.
>
> 3) If you have a 10:1 reduction, your maximum speed is 600 RPM. You
> have run out of RPM.
>
>
> Step motor:
>
> 1) Torque is the inverse of speed. If you need 600 in-oz, you use a
> 600 in-oz motor.
>
> 2) Your reduction ratio is 1:1
>
> 3) You still have usable torque for rapids at 1,500 RPM.
>
> Or try it this way: You have a car with a manual transmission.
> Unfortunately it has only one gear, 1st. You red-line at 20MPH; you
> have run out of RPM.
>
> Same car, same horspower but now a 5-speed transmission. You red-
> line
> at 120 MPH. You still have usable torque for your 120 MPH "rapids".
>
> ---------------------------
>
> Doing work takes power so power is everything. It is the mother of
> the twins named Torque and Speed. That's why you don't see NEMA-
> 17
> motors driving Bridgeports no matter how suitably geared.
>
> Physics is neither deceptive or cares if it's agreed with or not.
It
> simply is.
>
> The example I set up was a practical one. Though at its limits, the
> stepper is delivering 600 in-oz of torque, else how would I be able
> to measure it? The servo also is at its limits at 60 in-oz, go
beyond
> that and it will burn up. That is a fair comparison.
>
> The servo needs a 10:1 reduction to get 600 in-oz. Its 7,500 RPM no-
> load gets turned into a maximum possible 750 RPM. Looks on the
level
> to me.
>
> The stepper torque measures 100 in-oz at 1,600 RPM. Dyno says so;
> the
> same dyno that also ran on the servo. My calculator agreed by
> predicting what the dyno would say except it said 1,683 RPM. Seems
> honest there as well.
>
> So. The critera of 600 in-oz at 150 RPM (30 IPM on a 5 TPI screw)
was
> met and exceeded by both. The stepper held that torque out to 300
> RPM.
> The servo could deliver that torque out to 685 RPM but so what? It
> was only necessary to 150 RPM.
>
> The other criteria, a 100 in-oz rapid, was won by the stepper at
> 1,600 RPM to the servo's 725 RPM. Why? The servo "red-lines" (runs
> out of RPM) at 750 RPM.
>
> My point is a servo has an unfavorable speed-torque curve compared
> to
> a stepper's for a hi-torque/low-speed, hi-speed/low-torque dual-
mode
> operation. The above is intentionally set up to point it out.
> Comments?
>
> Mariss
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Polaraligned"
> <polaraligned@o...> wrote:
> >
> > >
> > > OK, so my question is about power in the calculation. at what
> point
> > > do you select power for either type of motor ?
> >
> > Don't. I don't agree with Mariss that power is the bottom line.
> > You need to select a torque and RPM curve that fits your
> > application. Power is just the result of these 2 factors, but
> > not something to be directly chosen. The Power number in Mariss'
> > calculations is what made the servo appear to be performing worse
> > than the stepper. The example he posted is completely deceptive
> > since he is assuming that the servo is putting out maximum power
> > when it is rapiding. That is not the case. At slow cutting
speeds,
> > the servo is actually using less power than the stepper, yet this
> was
> > not pointed out. Where do you spend your time, cutting material
or
> > doing rapids?
> >
> >
> > >
> > > Is my NEMA42 800oz in motor just as good as a NEM34 800oz-in
> motor? I
> > > thought there were reasons the NEMA42 were not as good.
> >
> > NEMA is just a frame size and has no bearing on the motors
> performance.
> >
> >
> > > As for servo's. how do you calculate for a 230 volt motor that
is
> > > rated for 1-1/2 hp and 5,600 rpm when you are going to use a
> Gecko on
> > > it with a 66 volt power supply ?
> >
> > Sounds like trial and error to me.
> >
> >
> > Scott
>
>
>
>
> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
> Post Messages: CAD_CAM_EDM_DRO@yahoogroups.com
>
> Subscribe: CAD_CAM_EDM_DRO-subscribe@yahoogroups.com
> Unsubscribe: CAD_CAM_EDM_DRO-unsubscribe@yahoogroups.com
> List owner: CAD_CAM_EDM_DRO-owner@yahoogroups.com,
> wanliker@a..., timg@k...
> Moderator: pentam@c... indigo_red@q...
> davemucha@j... [Moderators]
> URL to this group:
> http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
> 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
>
> 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........
> bill
> List Mom
> List Owner
>
>
> Yahoo! Groups Links