Re: Bridgport clone Retrofit

Jon

Thanks for the info. The motors are rated at 1430 RPM. I'm not sure
if this is peek or what. I see your point about the cost of zero
backlash couplings. I looked at those and wondered if anyone was
using straight keyway sleeve couplings. Alignment seems problematic
but still I wondered if it was done.

The encoders are already mounted to the back of the servos. I do
have some concerns here. There are 9 total wires coming from the
servos. I'm guessing 2 for motor power, two for encoder power, and
the rest for encoder signals. But it seems like a quad encoder would
only need 2 wires. I know come servos have tachs or something called
a resolver.

Thanks for the info on the supply size. Do the Gecko drive regulate
the voltage to the servos, or do they supply a PWM signal to the
motors. I assumed that the Geckos just turned the motors on full
blast until the encoder step count matched the step count requested
by the control program. Does the Gecko provide some acceleration –
deceleration? I figured this was the job of the control program.

Thanks Again
Marc Davis

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
>
>
> Davis, Marc wrote:
>
> > Group
> >
> > I'm planning a Bridgeport clone (Alliant) retrofit.
I have
> >some servo motors from an old Bandit retrofit on a Mori Sieke
(sp?). Dana
> >7.5A 90V.
> > I'm thinking about using the Flashcut signal
generator and
> >Gecko G320 drives. I also plane to install ball screws.
> >
> > I think the servo motors I have are big enough to
direct
> >drive the X-Y. Any comments on this? How about the knee?
> >
> >
> Yes, that is 675 W, almost a full HP. This should be fine for a
> Series-I sized machine. I'm running motors
> up to about 5-6 A @ 75 V on a Series-I sized machine.
>
> > What methods are people using to couple direct drive
ball
> >screws. Is a keyed sleeve adequate? What about misalignment?
> >
> >
> Unless your motors are wound for extremely low speeds, a belt
reduction
> drive give several
> benefits. It takes care of all the alignment problems, and allows
for a
> very stout drive system.
> Zero-backlash couplings that can take the torque of a 1 HP servo
motor
> are VERY expensive.
> You can mount your encoders directly on the end of the shafts with
a
> helical-slit coupler that
> DOESN'T have to take much torque.
>
> > What size power supply do I need? 7.5A X 3 = 22.5.
Is it
> >that simple? I assume that 90V is the max drive voltage for the
motors and
> >that
> > lower voltage will work ok but limit torque and speed.
> >True?
> >
> The Gecko drives are not rated for use above 80 V. You won't lose
> torque, but you'll lose speed.
> But, you may have plenty of that, anyway. You don't need a 22.5A
power
> supply. That is a
> worst-case peak load. A well-made 10 A supply should suffice, and
a 15
> A would be just fine.
> All unregulated bulk supplies are designed to take a peak load when
> motors are starting.
> Also, the switching nature of PWM power supplies allows them to
draw
> much less current
> at the input than the output is delivering when the output voltage
is
> well below the DC supply
> voltage. This is the most common condition, where the motors are
> accelerating from a stop,
> or reversing from low speed. The voltage on the motors is low when
they
> are turning slowly.
> And, you rarely need peak torque AND high speed at the same time.
>
> Jon
>