RE: [CAD_CAM_EDM_DRO] How do you compare steppers to servos

I think Art hit the nail on the head.



A few other points to ponder:



1) Why did the OEM of the system you were looking at specify a 260
oz-in motor? I have found that many times this choice gets made by just
slapping on the biggest stepper motor that a particular drive can handle.
This seldom leads to optimum performance.

2) The choice of stepper drive can make all the difference in the
actual power a motor can deliver. Big motors are often a (poor) substitute
for a good quality stepper drive.

3) What advantage will servos have over stepper motors for this
machine? For most small CNC machines there is no benefit to servos, other
than having positional feed back. Both drive systems will stall if
overloaded and both will maintain accurate position if not overloaded.



Jeff Birt

Soigeneris.com



From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Art Eckstein
Sent: Friday, February 25, 2011 11:17 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] How do you compare steppers to servos





IF you want to match the torque speed characteristics of the stepper
system, find the torque curve for that stepper motor.
At the max rpm of the stepper, note the torque it will produce at
this working point. The holding torque is relatively useless for
figuring useable torque at speed.

Now, you have the basic information you need. It is a balance of
tradeoffs between torque and speed with the servo. Let us assume the
max speed of the stepper is 750 rpm. Most servo motors are rated at
relatively high rpm say 3000. To match the rpm of the stepper, you
will need a reduction of 3000/750 or 4:1. No take the torque rating
of the stepper (at speed, not the holding torque) and divide by this
ration (4) and this will give you the minimum CONTINIOUS torque
rating you want from your new servo.
From this, I hope you get the idea and proceed from there.

Art
AKA Country Bubba

At 12:01 PM 2/25/2011, you wrote:

>Suppose a system is advertised using nema23 steppers of some size,
>say 260 oz-in.
>
>You want to build the same system but instead use servos.
>
>How do you compare the compare power of the the steppers to the servos
>
>thanks
>Glenn

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