Re: [CAD_CAM_EDM_DRO] Re: Mariss' Surplus Center Motor - Thanks

I realized the relationship between the high torque/low RPM and low
torque/high RPM for the *SAME POWER*.

The Amateks and the PacSci motors are *NOT* the same power, however, or
at least they don't appear to be. The Amateks are 40V, 10A peak whereas
the PacSci motors are 120V at various currents, continuous, with varying
peak powers. 2HP, etc.

My discussion of the Kt of the Amateks versus the PacSci versus the
Baldor was to relate what the current ratios might be for a similar
torque loading, ie an Amatek or a Baldor with a Kt of 50 ozin per amp
will take half the current that a PacSci will take (at 25 ozin/amp).
Where we might be approaching 5A on a heavy cut with Amateks, we'll
probably be at 10A with the PacSci.

I fully understand that a PacSci runs faster, develops more power and
has a higher current capability.

Kim

On Wed, 2003-10-22 at 10:51, Mariss Freimanis wrote:
> Kim,
>
> Kt is always 1.351 * Kv, so any motor having a high torque constant
> will also have a large Kv. That stands to reason; for the same power
> output you can have either a high torque, low RPM motor or visa versa.
>
> Mariss
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Kim Lux <lux@d...> wrote:
> >
> > I've been looking at these motors too for our next conversion. They
> > have got higher RPM limits than Amateks. They are going to take
> more
> > current, however as the Kt is about 25-30 ozin/Amp whereas the
> Amateks
> > are 50 ozin/Amp. We never run the Amateks over 5 amps anyway, so
> these
> > should run under 10 amps.
> >
> > BTW: there are several similar motors of different speeds, voltages,
> > power and current.
> >
> > For the Z axis (Knee) on our next conversion, we've chosen to use a
> 3130
> > (1/2HP) Baldor DC motor. It is rated at 4.6 amps continuous, all day
> > long and has a KT of about 50 ozin/amp, for about 225 ozin all day
> > long. We are driving a 4TPI 1" ballscrew gear reduced 1:1.25 to
> get an
> > effective 5TPI direct, which with our encoders gives us 0.0001"
> steps.
> >
> > I did some calcs and found some discrepancies between their torque
> > numbers and their stated powers. I think the powers are peak.
> > Hopefully the torques are continuous.
> >
> > Kim
> >
> > On Tue, 2003-10-21 at 21:40, Mariss Freimanis wrote:
> > > Roger,
> > >
> > > Thanks. Anything made by PacSci is going to be of excellent
> quality.
> > >
> > > Let's do a little math here:
> > >
> > > Assume you are looking to get 100 IPM on the Z axis. A 10
> turns/in
> > > screw would have to spin at 1,000 RPM to do that.
> > >
> > > 1HP is 396,000 in-lbs/min; it would take .303HP or 226W to lift
> 1,200
> > > lbs at 100 IPM (1,200 lbs * 100 IPM / 396,000 = .303HP). This is
> easy
> > > work for a 500W motor.
> > >
> > > The motor would have a no-load speed of 3,000 RPM at 75V (75V/25V
> *
> > > 1,000RPM = 3,000RPM).
> > >
> > > Figure on the motor developing its rated power at 80% of no-load
> > > speed. That would be 2,400 RPM.
> > >
> > > The correct reduction ratio would be 2,400 RPM / 1,000 RPM for
> the
> > > lead-screw. That is a 2.4:1 reduction.
> > >
> > > It would require 306 in-oz of torque on a 10 TPI leadscrew to
> lift
> > > 1,200 lbs (in-oz = 8 * lbs / pi * TPI = 8 * 1,200 / 3.14 * 10 =
> 306
> > > in-oz).
> > >
> > > A 2.4:1 reduction would place a 127 in-oz torque on the motor
> (306 /
> > > 2.4 = 127).
> > >
> > > The motor's Kt is 33.8 in-oz/Amp. This means the motor would draw
> > > 3.77 Amps while lifting 1,200 lbs at 100 IPM (127 in-oz / Kt =
> 3.77A).
> > >
> > > The motor would stay very cool at that current.
> > >
> > > Mariss
> > >
> > >
> > >
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "vrsculptor"
> > > <vrsculptor@h...> wrote:
> > > > Mariss,
> > > > Thanks for the tip on the Surplus Center motors. I got two of
> them.
> > > > They are Pacific Scientific treadmill motors, real well built.
> They
> > > > spin at about 30 rpm with a single D-cell. They have flat
> endplates
> > > > with 2 1/4-20 through boltssoend mounting them will be a layup.
> > > >
> > > > I'm planning on using one as a knee motors on my large servo
> mill.
> > > > If its well enough built to run on a flashlight battery it
> should
> > > > have no problem with 76 volts at 10 amps. I unfortunately won't
> > > have
> > > > any time until after Thanksgiving to mount an encoder and do
> real
> > > > testing.
> > > >
> > > > I just hope it can lift a 1,200# table/knee with a 2 or 3:1
> belt
> > > > reduction on the motor and a built in 10 turns/inch helical
> > > > gear/ballscrew jack. The knees ways are turcite lined and
> pretty
> > > > slippery.
> > > >
> > > > Roger S.
> > > >
> > > > Mariss wrote:
> > > > "I stumbled across this motor:
> > > >
> > > > http://www.surpluscenter.com/item.asp?
> UID=2003070308293941&item=10-
> > > > 1931&catname=electric
> > > >
> > > > It's rated at 4800 RPM at 120VDC with a continuous rated torque
> of
> > > > 250 in-oz. Working the numbers gives a Kv of 25 volts / 1,000
> RPM
> > > > and a Kt of 33.8 in-oz per Amp.
> > > >
> > > > At 72 volts you would get 2,880 RPM and draw 7.4 Amps at its
> rated
> > > > torque. The power output would be 533 Watts or about .71 HP. I
> don't
> > > > have this motor nor have I tested it with our G320 drive but it
> may
> > > > work.
> > > >
> > > > At $24.99 it may be worth a gamble.
> > >
> > >
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> > Kim Lux <lux@d...>
>
>
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>
> 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
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
--
Kim Lux <lux@...>