Re: MircoStepping Drive Which One?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Monte" <montejw@e...> wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Fred Smith" <imserv@v...>

wrote:

>
> >
> > These are bipolar, $65 per axis with more features and more durable
> > than the Xylotex (ie opto isolated, rated for 3 amps at 35v, single
> > power supply, etc):
> >
> > http://www.pmdx.com/PMDX-150/index.html
> >
> > Fred Smith - IMService
> > http://www.cadcamcadcam.com/hobby
>
> The Xylotex only needs a single power supply. Gecko's need 2, motor
> power supply and logic power supply.
>
> Monte

I'm confused here. The PMDX card has opto isolators but states step
and direction are ground referenced. Which ground? Is the motor DC
share the same ground with the PC ground? I don't see anything on the
board that would indicate that there are split grounds. If they do
share the grounds why bother with Opto's? Yes, they will increase the
noise immunity some but don't isolate the grounds where a lot of the
noise develops.

There is nothing wrong with a common ground driver for smaller
applications but just having opto's to isolate the signal does little
to offer true galvanic isolation like the Gecko's.

The Xylotex card uses the same exact chip and rates their card at 2.5A.
30V. The only difference appears that the PMDX was a more efficient
heatsink design. There are definitely more features on the PMDX. I
think the price is reasonable with the added features, but from an
operational perspective I doubt there is a lot of difference when you
get down to spinning the motors.

On a cost basis the Xylotex is still the winner at $175 for 4 axis VS
$260 for PMDX and $456 for Gecko's.

From a servo perspective Fred's 30V 5A servo cards are the best deal
for smaller servos.