Closed loop with linear encoders but still backlash?

wow , that all makes sense... So thats the trick, Thanks Andy.

That means, using the 7i98 as an example, would cost me at least $237 ( 7i98 (Controller Only) - $99 / 7i78 (Step&dir) - $69 / 7i85 (Encoders & RS422) - $69 / =$237), having the basic required IO in place.

And using the 7i96m would cost me $188 ( 7i96 (Controller + 4Stepper IO + 11 GPIO.in + 6 GPIO.out) - $119 / 7i85 (Encoders & RS422) - $69 / =$188)

I however do not see support in pncconf for the 7i85... but maybe this is not needed, because of.... some reason ??


And for your question about the Spindle-Drive. Currently only "on/off/CW/CCW" are planned using GPIO. But the next uprade will involve a PWM or Potentiometer controlled Spindle-motor-driver.

That leads me to this:
Is any of you thinking of writing a book about LinuxCNC+Mesa Cards, and practical application for CNC-Conversions ? I would buy 2 !. But serious, is there a good information-base, where one can first read & absorb all the basics about LinuxCNC, Mesa-cards for practical application ?
I have seen so many Youtube movies, read so many Forum-threads... but not once, have I seen, a complete example
(Like: 1. This is my Lathe / 2. This is LinuxCNC & my MESA-Card I am going to use -> And now I am going to show you step-by-step, how to do this conversion & Tuning).
Is there any Source you would recommend me to fully absorb first, before I take your precious time again and ask not-so.educated questions ?

I really appreciate the help, because your answers really helped me. I hope I can once return a favor.

BR,
R.

Dear Andy,
All the machine IO‘s are shown in the pdf I attached to my initial post from today.
You should be able to see all the used steppers & encoders.
But basically, it is the basic full-Feedback Lathe cnc conversion using steppers, core components:
2x stepper motors
2x linear encoders for x & z (Incr. AB Z)
1x spindle encoder (incr. Quadrature, ABZ)
1x spindle Motor
2x Limit Sensors
The rest is shown in the pdf.

R.

Thanks again Andy, great to hear that the 7i96 + 7i85 seems to be a good fit for a Full Feedback (or Closed-Loop) CNC-Retrofit for a Lathe.

I see the SW-package for the 7i96 supplies a BIT-File for the 7i96 + 7i85 Combination (7i96_7i85d.bit), which is great. However, if you try to do the configuration using Pncconf, you find that you cannot select the 7i85 from the drop-down list (Picture from Message #188431)... so how can one now assign the needed LinuxCNC-Signals to the 7i85 Card ?

To change a plain step/dir 7I96 configuration to one using encoder feedback
is fairly simple with minor hal file edits, just change the position feedback
source from the stepgen to the encoder (one statement per axis).
Of course the PID tuning will be very different.