> -----Original Message-----
> From: Nicklas Karlsson [mailto:nicklas.karlsso...@gmail.com]
> > > -----Original Message-----
> > > From: Chris Albertson [mailto:albertson.ch...@gmail.com]
> >
> >
> > > The STM32 has no problem with MHz level bit flipping.   Reading or
> > > creating is MHz level is not hard.
> > > And the Pi3 has to be about the most well understood and documented
> > > machines on Earth.  they
> > > are ultra-common.
> > >
> > > The pi still is beat by an Intel desktop PC but the Pi has that GPIO
> > > header and you can get at signals.  The OS causes unpredictable
> > > latency so use the STM32 if that matters.
> > >
> > > As for compute power if the Pi is not enough you offload from the Pi
> > > to the bigger box.    But for machine tools the Pi is overkill unless
> > > you are doing vision.
> > >
> > And the STM32s are so inexpensive that the STMBL AC Servo drive uses
> two of them.  One to handle the actual 3 phase drive output and one to deal
> with the encoders and user interface etc.  It's a nice solution where the
> computer side (LinuxCNC) is electrically isolated from the 350V Motor side.
> There are good reason to place Micro controller on rectified negative rail
> while other signal need to be electrical isolated. This might be the reason
> two micro controllers are used.

Other than frame ground an AC Servo using 350VDC derived directly from the AC 
power line (w/o a transformer) must never have that 350VDC connected in any way 
to the instrument DC logic (or even transformer isolated DC relay/stepper 

So now you have the issue of an encoder that uses 5V.  Intelligent Serial 
Control or Step/Dir or even quadrature position signals all at 5V logic 
referenced to the instrument bus.  Either optically couple all that at the 
input of the AC Servo controller (gets expensive in both parts and board area), 
or just use two processors on two boards with a high speed control signal 
between them that is optically and physically isolated.

Once again shows how clever the designers are.   Were it not for the 
discontinued driver device there would be many more of them out there.  The 
size of this unit given the power capabilities is very small compared to a lot 
of other units out there.  My issue right now is finding an inexpensive 3 phase 
2HP motor I can swap into my Mill Spindle.  Ie. I have the cart  but not the 

John Dammeyer
> Nicklas Karlsson
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