Re: What makes a motor a servo? gearing servos

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Alex Holden <alex@l...> wrote:

> On 11 May 2005, at 5:11 am, Mariss Freimanis wrote:
> > 2) If you need 600 in-oz, you have to have a 10:1 reduction.
>
> Would anybody really try to drive a machine with a servo motor so
> underpowered that it needed to be geared down 10:1 to get enough torque?
>

It's not so much that they are trying to mis-fit a motor, but that
servo's sweet spot is about 80% of it's (no-load ?) RPM

So, if you have a 2500 RPM motor and want 150 ipm rapids, on a 5 pitch
screw, you need to gear the motor so the screw is spinning 30 rpm.

Working from there, if you need 1500 oz-in on the screw, you only need
an 150oz-in motor

Now the rub is that guys pay a premium for a 1500 oz-in stepper, but
others have a hard time finiding servos as small as 150 oz-in.

So, the stepper guys may use 2:1 or 3:1 gearing and servo guys buy
bigger motors and gear 4:1 to 9:1. Others may go direct drive.

Starting with a motor selection point of view, and not what is
available surplus point of view, the comparison is probably in the
ball park.

I mentioned a week ago that the reason so few people use steppers and
so many use servos is that the beginner starts with underpowered
steppers and crashes, then replaces with hugely overkill servos and
never looks back at what happened.

The 'stepper crowd' reports that doing it right in the first place
works. the 'servo crowd' reports not only working, but having a huge
potential surplus.

Just an observation.

Dave