Re: EMC configuration help

[Ray <rehenry-at-up.net>]

Erich (comments mixed in)

On Friday 23 November 2001 08:23 am, Erich wrote:
> Ok people one more try.
>
> On Thu, 22 Nov 2001, Henry Palonen wrote:
> > Ah. Sorry, I forgot the [1] link:
> >
> > [1] http://www.linuxcnc.org/handbook/faq/faq.html
>
> This I did read. Still not getting the meaning of life and
> everything....
>
> > Henkka
> >
> > * Henry Palonen (henkka-at-yty.net) [22.11.2001 18:11]:
> > > Hello Erich,
> > >
> > > There is FAQ regarding this at [1]. I'm copying it here for your
> > > convience:
> > > ----
> > > EMC: How to I set the steps per unit for each axis? (TOC)
> > > INPUT_SCALE and OUTPUT_SCALE are number of pulses for each unit as
> > > defined in the UNITS = line. One for mm, 0.03937007874016 for inch.
>
> What is this odd number? And why should I take that as a unit?

This number is the conversion between mm and inch accurate to enough 
digits to make long moves possible without introducing much math error.  
If you plan to run this machine in mm, you might ask how the mm folk set 
their machines up.  We inch folk leave this the way it is but I've heard 
of some setting this value to 1.

> > > Using inch and steppermod, you just need
> > >
> > > INPUT_SCALE =           8000 0.000
>
> What do the _two_ numbers represent? Why use INPUT_SCALE (I do not
> have feedback via DRO)?

I think that the appropriate way to think of these is that the input scale 
represents how many pulses you need to input to the motor amp to get one 
unit of motion.  Output scale is the number of pulses the encoder will 
send for one unit of motion.  Motor or axis in and out rather than PC in 
or out.

> > > With inch and freqmod selected you need both
> > >
> > > INPUT_SCALE = 8000    0.000
> > > OUTPUT_SCALE =  8000    0.000
>
> Again, what do the two pairs f numbers represent in laymans terms? For
> what real pitch and stepper motor would this example apply?

This would be 8000 pulses per inch or mm depending on what you defined in 
that funny number (UNITS) above.  The input scale would say your PC should 
spit out 8000 pulses into the axis amp to get a unit of motion.  If you 
wish to reverse the direction of motion with respect to the EMC internal 
motion model you can reverse the sign of the number.

Output scale says that you should also get back 8000 pulses for a unit of 
motion.

My Grizzly mill uses five tpi screws, a 3/1 belt reduction, and two 
microsteps per step with 1.8 degree steppers (200 steps per rev).

5 x 3 x 2 x 200 = 6000

so that is the number I would enter as input scale.  

Now using steppermod mod, output scale is not used.  The generic stuff 
sets it to 1.  Using freqmod you would need to set it to the same number 
as the input scale.  Using smdromod you would set it to the number of 
pulses returned from the encoder connected to that axis when it moves the 
distance caused by one unit of commanded movement. 

> > > With inch and smdromod selected you can change the value between
> > > input and output.  Input would be the number of steps per unit on
> > > the stepper motor and output would be the number of pulses reported
> > > by the encoder per unit. Since output scale is written back into the
> > > ini, they may look a bit different that you ente after you run once
> > > but setting them as suggested above should do the trick.
>
> Sorry to bother you with my ignorance again. I do not get the curve
> here. How can I apply the above to my setup? I have a metric leadscrew
> with 5mm/rev and 200 steps/rev motor. how does this tie in to the
> conf.ini in the axes section? (I hope I can work out the 1,5mm/rev and
> 200steps/rev z-axes myself then)

Hey, you can't be very ignorant, you made the decision to use the EMC. <g> 
If I were doing this using the inch UNIT value, I'd first have to convert 
the 5mm pitch screw.  That's 5.08 turns per inch times 200 steps per rev 
for direct drive and you get 1016 for input scale.  

You can also crib this number if you use cheap ball screws that run long 
or short to bring your actual distance moved closer to commanded.

Hope this helps.

Ray