PM-940TV 7i96s spindle virtual potentiometer config help

Hi guys,
I searched/read about this topic but I did not get it to work (I did not understand the matter), so I'm asking here.

I have almost converted my first "big" mill (PM-940TV) to cnc, and I have now to configure to control the spindle speed.
I'm using a 7i96s that has three pins called spind+ cursor spind-
I've replaced the analog potentiometer in the mill head with wires going to these three 7i96s pins.
The mill board has 12V cursor and 0V on that potentiometer, So I've connected the 12V to spind+ the cursor to the cursor and the spind- to the 0V.
The spindle direction is working by two relays connected to two output from the mesa and they work ok.

BUT the speed is not working.

I'm using linuxcnc 2.9.8 adn QTDragon-hd.

Reading the linuxcnc docs I see there are different ways to control the spindle speed... but I did not understand which I should use with this virtual potentiometer...

Could some of you point me in the correct direction please?

At the moment when I switch the spindle on it stays at 50rpm (the minumum speed of my milling machine) even if I send a S1000M3 (see the 1000rpm on the display of qtdragon_hd but the actual spindle speed remains 50rpm).
Max speed of my mill should be 4000rpm

Thanks guys,
have a nice day,
Alberto.
 

Ok, Now it's working... I found a post here with this:

# ---PWM Generator signals/setup---

setp [HMOT](CARD0).pwmgen.00.output-type 1
setp [HMOT](CARD0).pwmgen.00.scale [SPINDLE_0]OUTPUT_SCALE
net spindle-vel-cmd-rpm => [HMOT](CARD0).pwmgen.00.value
net spindle-enable => [HMOT](CARD0).pwmgen.00.enable

it's working... I only have some "scale" problems...

the actual speed capabilities goes from 50 to 4000RPM.

BUT wihth S50M3 it goes to 104rpm... 
to get it to 50rpm I need to send S1M3.

testing I'm getting:
S1M3 => 50rpm
S3450 => 4000rpm

How can I set this to be:  
S50 => 50RPM
S4000 => 4000RPM
?

Thanks.

 

You could use the hal scale  component to subtract 50 from the commanded spindle speed,
something like:

loadrt scale
setp scale.0.gain 1
setp scale.0.offset -50
net spindle-vel-cmd-rpm => scale.0.in
net fixed-spindle-rpm scale.0.out  [HMOT](CARD0).pwmgen.00.value
addf scale.0 servo thread

 

Thanks PCW,
I will try this morning