Setting up lathe speed with 7i76 digital pot

I just measured across spindle- and spindle+ and there was no AC there, only DC.

I've also managed to get .spinout to track commanded RPM in both low and high range by editing the scale.

One thing you might try first is to run the drive with a isolated power source supplying the potentiometer. If this works, the 7I76E Digital potentiometer should as well.

I don't think I'll have time to try this tomorrow before I leave for work, but I'll try when I get back sometime early February.

Anyway, thanks for the help so far.

You will need to tine it in the VFD and the Belt gearing of the machine.. See my unfinished build!! www.stevenrhine.com/?p=2432

It took a bit longer longer than February before I managed to test this (it was barely above freezing in my workshop when I came back from work in February...), but I've tested now. I connected a separate 12V DC PSU with negative from PSU to both digital pot negative and motor controller and positive to digital pot positive.. This helped and I could adjust the speed of the spindle from PP, but now I need some help setting up the sale properly.

I did a few quick tests. The PSU is 12V and when I commanded S200, I had 1.32V and a speed of 180RPM. With S400, I had 2.64V and a speed of 600RPM.

Since PP uses a bit different configuration for spindle speed than vanilla LinuxCNC, how do I calculate the scale and which parameters do I use?

Br,
Stig

It sounds like the scale might not be far wrong, but the linearity is not all that you might wish.

The 7i76 sounds to be outputting exactly he right voltage for a 1500 rpm spindle. But the actual spindle seems to not be responding linearly.

You could consider setting up a PID for closed-loop spindle speed control, or maybe tweak the commanded rpm with the "lincurve" HAL component.

Or you could not bother, as all that really matters if if the spindle speed is "too fast" or "too slow" and the actual numbers are not 100% relevant.