Hi Andy, 
See below.

> -----Original Message-----
> From: andy pugh [mailto:bodge...@gmail.com]
> Sent: April-10-19 2:46 AM
> To: Enhanced Machine Controller (EMC)
> Subject: Re: [Emc-users] Leaving an axis out of the home sequence AND
> (continued:)
> On Wed, 10 Apr 2019 at 04:49, John Dammeyer <jo...@autoartisans.com>
> wrote:
> > Since my Harmonic Drive/STMBL are an AC Servo
> ...
> > The question then is whether or not the system, when starting can/will
> recognize an input which is a unit present signal.
> This is a solved problem :-) (I have exactly the same 4th axis as you)
> I have a loop of wire on two spare pins on the connector where the 4th
> axis plugs in to the machine:
> This drives an input on the STMBL. The STMBL HV enable is only set
> (HAL Logic) if this input indicates motor-present.
My HP_UHU drives have that feature built in.  The encoder connector has to have 
a jumper to show the encoder is connected.  Probably to avoid a runaway 
> I just accept having an A axis display even when the axis isn't
> connected. And the machine will f-error if you try to move or jog it.

I'm testing with both MACH3 and LinuxCNC so I can write up a neat little 
conversion document that takes a parallel port BoB based system from MACH3 into 
LinuxCNC with minimal pain.  In the MACH3 system, on my CNC router, when I tell 
the open loop stepper controlled axis to home all that MACH3 does is zero out 
the DRO.

But Gene has a home switch on his rotary indexer.  Now thinking about it I 
think the solution might be simple. When he pulls the indexer off the mill he 
has to unplug the encoder cable.  If he's using safe type limits then the 
switch is normally closed and a home (or limit) happens when it opens.  

So run the home switch circuit through the encoder connector and wire the 
mating encoder connector to have the connection closed.  From the CNC 
controller perspective the system is already homed.  The only problem will be 
if LinuxCNC uses a find home switch sequence, and then backs off so the switch 
just opens again before it declares it's home.

In that case it would try to move off a non-existent home switch and try 
turning the indexer forever.  And perhaps that's again where that extra input 
comes in.  If the input is asserted then a home switch exists.  If it's not 
asserted then a home switch doesn't exist and he runs it like you run yours or 
I run mine.

Again in the MACH3 situation, all I have to do is select the ports and pins 
menu selection under the config menu.  Select inputs and uncheck Home switch 
for A axis.  That also hits the software ESTOP and shuts power down to the 
drives when I click OK to save.  I can now unplug the A axis and remove it.  
Then press the now blinking RESET button, power is back and a HOME command just 
clears the A axis DRO.  Simple.  No file editing.  No multiple config copies.

That's what is really needed on LinuxCNC.  


> It might be possible to load different configs depending on that
> signal. A bash script can send halcmd commands to load the hostmot2
> driver, start the threads, read a pin, and then run one of two or more
> linuxcnc startups (after unloading Hostmot2 and realtime, probably.)
> Maybe even an edited version of the LinuxCNC startup script:
> Personally I haven't cared enough about the vestigial axis to bother :-)
> --
> atp
> "A motorcycle is a bicycle with a pandemonium attachment and is
> designed for the especial use of mechanical geniuses, daredevils and
> lunatics."
> � George Fitch, Atlanta Constitution Newspaper, 1916
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