Re: servo vs stepper

Thanks Bob, I have a belt drive with a 2:1 reduction to a 5 pitch
ball screw using a timing belt. This machine was CNC so all the ball
screws and pulleys were already installed.

What is strange to me is that the geckos are not working even though
the motors are rated at 7 amps. The motors stall at 5 rev/sec on the
bench. I know there is very little mechanical load on at least the z
axis. All three axes stall at about 20 ipm and it is not location
dependent. The original Bridgeport Sigma motors stalled at exactly
the same speed. Do you have any suggestions at to what motors you
have had success with and the oz/in ratings? I am using a Nema 42
motor that should be able to go 20 rev/sec at 7 amps before stalling.

Thanks
Keith Clark

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Bob Muse" <mtebob1@s...>
wrote:

> Hi Keith
>
> I have not been following this thread that closely but having done

a fair

> number of retros including series I and series II BP's I would

encourage

> you to hang in there a little longer before giving up or scrapping

what you

> have and going with servos. I spent a lot of time (being as how I

had time

> but no $$) playing with steppers before I got a good handle on them.
>
> I think the geckos should work very well. Just a couple of other
> thoughts/questions that may have already been mentioned but here

goes-are

> you using ball screws? How much friction in your ways, are you

getting good

> lube flow? I see you mention that your motors are high-inductance,
> generally that's not that desirable it probably would be better to

rewire.

> How is the motor coupled to the leadscrew? My series I used lovejoy
> couplings with rubber inserts and I think it helped quite a bit.

Had to

> change the rubber twice a year or so.
>
> The learning curve can be frustrating but having the CNC is worth

the

> effort.
>
> Bob
> ----- Original Message -----
> From: "Keith Clark" <mail@t...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Thursday, September 02, 2004 6:47 AM
> Subject: [CAD_CAM_EDM_DRO] servo vs stepper
>
>
> > As many have read, I have been having a bad time making stepper
> > motors work using Gecko drives. Several have recommended

switching

> > to servos but I have been fearful of tuning the motors etc. Is it
> > really that difficult and that much more expensive? At this

point I

> > have spent $550 on each motor. I am also concerned about the
> > difficulty of selecting the correct servo motors since I have had

so

> > much trouble with the stepper motors. I guess I would appreciate
> > some encouragement or discouragement at this point especially from
> > those of you that have done it with a Bridgeport. My machine is a
> > Boss 6 Bridgeport.
> >
> > Thanks
> > Keith Clark
> >
> >
> >
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