Re: How do you compare steppers to servos

Thank you Jeff for the points to ponder

My question was prompted by trying to decide if I wanted to go with the fully
turnkey version of the Monster Mill you offer, steppers 5 tpi leadscrews and windows.

OR

Play around with the Monster MIll using servos and electronics from Pico Systems(Jon Elson).

Windows gets me going fast and painless, but the dark side keeps callinnnnnng.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Jeffrey T. Birt" <birt_j@...> wrote:
>
> 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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> [Non-text portions of this message have been removed]
>