Re: Declining motor torque with lower voltage.

I was talking a 9 x 42 bridgport knee...Big difference wow....

I have not learned the calculations for force thru a ballscrew yet.
That would tell us how much torque you really need...

Wally


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Polaraligned"
<polaraligned@o...> wrote:

>
>
> Using your example
> > of Z table weight I think your numbers are off. I think an empty

Z

> > weighs a couple of hundred pounds, and fully loaded with vises

part

> > ect, specs out at 750 lbs. So unless you added 300 to 400 lbs

weight

> > to your table to test it, you do not have real numbers yet.
>
>
> Shipping weights from Bridgeport:
>
> Knee 257#
> Saddle 142#
> 48" table 365#
>
> Total= 764#
>
> The number for the table sounds a bit high. My 42" table I can
> pick up and carry. I guess it is about 200#. Their weight maybe
> includes leadscrews and all.
>
>
> Scott
>
>
>
>
>
>
>
>
>
> >
> >
> > Wally
> >
> >
> >
> >
> >
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, R Rogers

<rogersmach@y...>

> > wrote:
> > >
> > >
> > > cnc_4_me <cnc4me@g...> wrote:
> > > Since you are running the motor aprox 38% below rated voltage

you

> > > cannot push the amps thru the motor to get full torque.
> > >
> > > I left out the current ratting before but here it is 18.5 amp.
> > > Armature resistance would be 130vdc / 18.5A = 7 ohm. At 80vdc

and 7

> > > ohm you can only make 11.4 amps. The torque per amp is 373 0z-

in /

> > > 18.5 = 20 oz-in. At 11.4 amps max current you get 11.4 x 20 oz-

in =

> > > 230 oz-in.
> > >
> > > If we use your speed reduction number above 61.5% and multiply

it

> > > times the torque of 373 oz-in we get 229.4 oz-in. Seems to

agree

> > > with ohms law calcs.
> > >
> > > Wally
> > >
> > > /// Isn't it possible that delivering the volts and current by
> > another means than a continual supply as is the case with a pulse
> > stream, that the current delivered in tiny spikes rather than a
> > continuous flow would counter the resistance of the windings?

We're

> > not running these motors at top speed either, and very rarely do.
> > Would that also effect the resistance? All calculations aside,

when I

> > first started looking at B'port retrofit packages such as Ajax,

they

> > all told me a 28 lb-in motor was too small to drive the knee and

that

> > a 40 lb-in servo would be imperative. And nothing was guaranteed
> > especially the Z motor. I'm running a 100 volt 13.7 continual

amps

> > servo rated at 40 lb -in torque rating with a 64 VDC supply.

Using

> > the above calcualtion, I'm only getting 64% of the stated torque.
> > Which is 25.6 lb-in. It drives the Z at 60 ipm just as Ajax

claimed a

> > 40 lb-in motor would at full voltage. Calculations and theories
> > aside, it works. Remember,the knee table and vise weigh
> > > approximately 800 lbs. then add a few hundred pounds force of

a

> > drillbit plunging steel. The little Gecko320 tolrates this, much

to

> > my amazement. ///Ron
> > >
> > >
> > >
> > >
> > >
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