Re: [CAD_CAM_EDM_DRO] I need some help with servo's PLZ!!!! RETROFIT

twoextrememachine wrote:

>I thought a 600in/oz servo with 900rpm would have enough power to run
>my Knee mill. The individual I want to purchase a drive kit from
>does not agree with me (AHEM Camtronics) My table is 30" x 15"
>already running a cnc control that i am removing (don't ask why) The
>current motors are 500in/oz and 2000 rpm, i'm not concerned about the
>rpm because the spindle speed is going to restrict the feedrate.
>Additionally the 600in/oz motors would be running from gecko drives.
>How can i find out if this is enough servo or not, also let me know
>if this setup will work. This mill is a Shizouka with ballsrews.
>
>

Assuming a 5 TPI leadscrew, and 2:1 belt reduction drive, you'd get
1200 Oz-In at the leadscrew. This would give 2356 Lbs of linear
force on the table. If you went with a 1:1 drive, you'd still get 1178
Lbs of linear force! With the 2:1 reduction, you'd get 450 RPM on the
screw,
for 90 IPM. With the 1:1 drive, you'd get 180 IPM. These motors may
be able to go faster than 900 RPm with a light load.

Note that the problem with these motors is they have very high resistance
for this application, around 4.5 Ohm. This means to get 10 Amps through
the motor takes 45 V applied voltage, and that's with the motor standing
still.
If the motor is spinning at a speed that produces a back EMF of 48 V,
and you still want to get 10 Amps through it, you need 48 + 45 = 93 V,
and you can't get that out of a Gecko drive. I have a client in my area
that has these motors and Gecko 320 drives on a small mill (table is
7 x 28" or so) with a 10 TPI or higher Acme screw, and they are just barely
enough for it. He only has a 36 V power supply, which is part of
the problem.

For a machine with a 30 x 15" table, this may be marginal. If using a belt
reduction is acceptable, and you don't need high rapid feed rates, you
might be
able to live with these Ametek motors. If you want to direct drive the
leadscrews, and want to be able to at least jog the table around at 100+
IPM,
then listen to the Camtronics guy. There is no question that the Ametek
motors
will not give you high performance on a big machine like this.

Jon