Re: [CAD_CAM_EDM_DRO] Mixing servos & stepper in same system

Jon,
Thanks to you and Tim for the input. Based on your recommendation, I'm
going to use servos on all 3 axes, but when I design the motor mount for Z,
I'm going to be sure there's adequate adjustment, in the event I have to
play around with a few different timing pulley ratios.

Marv Frankel
Los Angeles

----- Original Message -----
From: "Jon Elson" <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Saturday, January 04, 2003 9:57 PM
Subject: Re: [CAD_CAM_EDM_DRO] Mixing servos & stepper in same system


>
>
> Marv Frankel wrote:
>
> >Guys,
> > I'm stilll doing R & D on my system components, and it was
> >suggested that I use a stepper to drive the knee's X axis, rather than
> >a servo, because of the steppers better low speed torque. Is there any
> >problem doing that, or would it accomplish the same thing by using the
> >higher speed servo, and just increase the gear ratio.
> >
> >
> Servos generally have full torque available up to top speed, where a
> stepper loses torque
> rapidly at higher speeds. With the servo, if you need more torque, a
> sprocket change will
> fix it, at the cost of lower top speed. With the stepper, changing the
> belt improves holding
> torque, but makes the running torque fall off even faster at the
> leadscrew. So, I would
> recommend servos for difficult applications. Since the motor will have
> to resist the
> steady weight of the knee, you might want to make sure your motor is
> plenty large
> enough to dissipate the heat, and that the Gecko drive (I'm guessing) is
> well heat sinked.
> And, you are likely to need a fail-safe brake that grabs the motor shaft
> when you go to
> e-stop mode or power off. That's only necessary for ballscrews.
>
> Jon
>
>
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