Re: Mariss' Surplus Center Motor - Thanks

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.
> >
> >
> > Addresses:
> > FAQ: http://www.ktmarketing.com/faq.html
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> --
> Kim Lux <lux@d...>