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

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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