Re: Servo question

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "zipdrive2k"
<zipdrive2k@y...> wrote:

> If a 600in-oz. stepper motor gives 'x' performance on a particular
> machine, is there some rule of thumb to get equlivant performance

out

> of a servo setup? Servo torque : Stepper torque? Or is this too
> simplified?
>
> Thanks.

One thing you can take into consideration is that a servo motor will
normally have much righer RPM capability than the stepper and it will
have much better torque at that high rpm. If you currently have the
rapids you are happy with using the steppers then you need to figure
the RPM of the screws under your current configuration. A that point
you should calculate a belt drive reduction on the servo setup so
that it will output the same RPM on the screws when the servo motor
is at 70 to 80% of it's max RPM. You will have to juggle motor specs
and the voltage ratings of the servo etc to get the RPM's. The final
result will be an proportional increase in torque. Bottom line is
that you trade the higher RPM of the servo's for increased torque at
the load so you can live with smaller torque rated servos than
steppers. Combine that with the actual torque you are seeing from
your 600 oz stepper at the higher speeds and you will find that you
can probably replace those 600oz steppers with 200oz/in servos and
get the same rapids and cutting force.

What you find is that you can usually do a 2:1 or 3:1 belt reduction
at the motor and double or triple your torque. My little 120oz/in
servos with 3:1 reduction and 5 pitch screws sling a 100 lb gantry
along at 160 IPM with no problem.