Mesa 7i96 spindle motor control / potentiometer replacement

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07 Nov 2020 05:16 #188571 by kbec
I have a Sherline motor with speed controller that I am trying to set up with my Linux CNC with Mesa 7i96 card. The speed controller uses a potentiometer with three leads to control the speed of the spindle motor. Is the 7i96 with Linux CNC capable of somehow replacing the potentiometer?, or do I need another add on card from Mesa to do this? It looks like my encoder is sending the right signals to the 7i96, but I would like to be able to control the speed with Linux CNC and not with the potentiometer if possible.

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07 Nov 2020 07:16 - 07 Nov 2020 07:20 #188575 by BeagleBrainz
You might be able to use this:
store.mesanet.com/index.php?route=produc...t_id=205&search=spin

You'll need to create a PWM signal. This is some documentation for spindle control, linuxcnc.org/docs/2.8/html/examples/spindle.html , you'll probably have to change from the PP pins shown in the examples to match your hardware.
PCW will probably have a better idea, but this maybe something to mull over.

Some stuff I found regarding PWM on the 7i96
forum.linuxcnc.org/27-driver-boards/3432...tions-for-pwm-output
forum.linuxcnc.org/38-general-linuxcnc-q...et-pwm-output-solved
forum.linuxcnc.org/27-driver-boards/3923...96-which-pin-for-pwm
Last edit: 07 Nov 2020 07:20 by BeagleBrainz.

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07 Nov 2020 16:03 #188592 by PCW
You have to be very careful as the potentiometer on many low-end speed controls
runs at line voltage potential. If this is the case with the Sherline you need to use
a fully isolated potentiometer replacement device. Mesa makes one (the SPINX1).
This is a simple small card that takes 3 signals (PWM ENA DIR) and provides a
potentiometer replacement plus isolated FWD REV and ENA outputs.

If the potentiometer does not run at line potential, you could use one of the 7I96s isolated
outputs and a RC filter to make a potentiometer replacement, something like this:



The schematic shows a 7I37 output but the 7I96 outputs are identical
This would be driven by a software PWM component in the hal file
Attachments:

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07 Nov 2020 16:07 #188593 by kbec
I did not see that card you mentioned, I think it would be really what I need. I will contact Mesa tech support and see what they say.

I am not really sure about trying to drive the motor with a PWM from the board. That seems it would totally eliminate the speed controller I have and there is a lot of specialized circuitry in there regarding torque, smoothness and such.

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07 Nov 2020 16:14 - 07 Nov 2020 16:14 #188594 by PCW
The PWM is used to generate the variable analog voltage in the
potentiometer replacement circuit
Last edit: 07 Nov 2020 16:14 by PCW.

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08 Nov 2020 01:31 #188637 by kbec
I get it, now I need that board you guys mentioned from Mesa.

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08 Nov 2020 09:57 #188658 by verticalperformance
The potentiometer on the KBIC controllers used by sherline does run at mains voltage. I use one of these http://homanndesigns.com/index.php?main_page=product_info&cPath=1&products_id=25 and drive it from the parallel port with no issues. Should be no issue driving it with a PWM signal from a mesa

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10 Nov 2020 04:30 - 10 Nov 2020 05:00 #188840 by kbec
I think the Mesa may work for me. I will see and let you guys know.
Last edit: 10 Nov 2020 05:00 by kbec. Reason: Could not delete it, fixed it.

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