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

OK, now I know where you are coming from. If you go for servos you'll need
to pick up some NEMA23 gear reductions or build a belt reduction. With
servos it is important to match the servo to the inertia of the system (the
mass of things that it needs to move), too big of a servo is as bad as too
small. A belt reduction can help as it can mask some of the inertia
problems.



Performance wise you will most likely not see any difference. The Turcite
coated gibs and lead screws on the monster mill provide very smooth
movement.



Jeff Birt

Soigeneris.com



From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Glenn
Sent: Friday, February 25, 2011 3:03 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] 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
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.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%40yahoogroups.com>

> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com

<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com> ] On Behalf Of Art Eckstein

> Sent: Friday, February 25, 2011 11:17 AM
> To: CAD_CAM_EDM_DRO@yahoogroups.com

<mailto:CAD_CAM_EDM_DRO%40yahoogroups.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
>
>
>
>
>
> [Non-text portions of this message have been removed]
>

[Non-text portions of this message have been removed]