Re: Bridgeport servo motors

Hi Scott, i was thinking about your setup some more and I am sure you
should use at least a 3 to 1 reduction. In the example below I
estimated your continuous torque by dividing your peak torque by 5.
I used 5 because many servos work out this way, but many also work
out to be 7. If you divide your peak torque by 7 you get 600 / 7 =
85.7 oz-in = 5.4 in-lb. Multiply this x 3-1 belt reduction = 16 lb-
in, or just enough power for heavy cut in steel (using my friends
estimation of force on hand wheel).

You also may have a little reserve in there, as Jon Elson pointed out
your peak torque may be 880 0z-in not 600. The reason being your
torque constant per amp is 44 oz-in and your peak safe current is 20
amps. Multiply them and get 880 oz-in. This would give you 880oz-in
= 55lb-in / 7 = 7.86 lb-in x 3-1 belting = 23.6 lb-in with 15 lb-in
estimated needed.

Wally



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

> > Well, this is what my research shows on required torque, speed,

and

> > reduction ratio.
> >
> > Most people on this forum agree the servo size used for

commercial

> > Bridgeport retrofits is around 30 lb-in or 480 oz-in.
>
>
> So this is the Peak torque rating for these motors?? I have been
> assuming that this is a continuous rating and my motors are a little
> small as opposed to being a little big.
>
>
>
> > Also I seem to
> > be getting the consensus that the pulley reduction is around 2-1

to

> > 2.5-1.
> >
> > Now let's look at a practical example. A friend has been using a
> > Bridgeport for 15 years. He is estimating that on average with a
> > heavy cut he is pushing 5 lb on the hand wheel. The hand wheel

has a

> > 3" lever length. So 3" x 5 lb = 15 in-lb continuous torque

needed.

> >
> > You motor has a peak rating of 37.5 lb-in. Estimating constant
> > torque we would divide peak by 5 = 7.5 lb-in. So you need 2x

this

> > number for the estimated 15lb-in force required. This tells me

you

> > need a minimum of 2-1 belt reduction.
> >
> > As you noted earlier more reduction gives you more power but

less

> > speed. A 3-1 reduction would give you a 22.5 lb-in at 80 IPM. A
> > nice continuous torque rating but a little slow on rapids.
> >
> > Lets talk about 80 IPM, I can tell you this. A typical power

feed on

> > a Bridgeport will give you a maximum speed of around 90IPM. If

you

> > have access to one of these you can see for yourself if you like

this

> > speed.
> >
> > From a personal standpoint, and this is coming from someone who

has

> > no patience….I get irritated using the power feed to go from one

side

> > of the table to the other. One time I actually disengaged it and
> > turned the crank by hand because I thought I could go faster (I

was

> > wrong). The reason for going from one side of the table to other

was

> > I had 2 setups on the table, one on each end…
> >
> > With that in mind I am shooting for a rapid of 120 IPM minimum on

my

> > machine.
> >
> > With all that said, if I were you I would probably go with 2.5

or 3-

> > 1 ratio, a fast rapid is nice. But if you can't take the cut you
> > want it doesn't do you any good.
> >
> > I also think you should use a 70 volt supply, with your current

limit

> > set to 20 amps. This way you will get maximum RPM without

running

> > over current.