First 7i96s/lathe build question: AC Servo driving spindle

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04 Apr 2024 05:11 - 04 Apr 2024 05:12 #297558 by EddySPalm
If I do end up using a servo, I was thinking pulse/dir from one of the step generators of the 7i96s. All the servo drives I am looking at do have the possibility for an index output, so that in itself should not be a problem, it's just that the 7i96s only has one encoder input without changing it's bit file, and I was planning on using that for an MPG. Also, I am not very programming savvy, so I must admit I dread that part of changing the bit file. 

I have not really landed on a spindle motor nor drive yet, though. I have access to both AC motors with vfd's and BLDC 48V 750W motors (would have to purchase a separate drive for the BLDC), but it is tempting to not have to purchase and install a separate endcoder, that's the main reason why I am leaning towards a servo.
Last edit: 04 Apr 2024 05:12 by EddySPalm. Reason: Extra info.

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04 Apr 2024 17:07 #297580 by PCW
You can use 2 pins on P3 for a MPG, leaving the encoder input free

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04 Apr 2024 22:27 #297602 by EddySPalm
Well that was good news. Thank you for your answer! Can any two of the P1 pins just be directly assigned as encoder inputs in pncconfig (or in hal?) and can I also simply connect directly to the pins? In that case I will get two separate handwheels and put them on a control panel instead.

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05 Apr 2024 01:06 #297615 by PCW
There are 4 MPGs Possible on TB3 but of course you lose 2 isolated input
pins per MPG. Its also possible to have MPG encoders on P1 but you have
to be more careful with P1 inputs.

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08 Apr 2024 09:57 - 08 Apr 2024 10:01 #297800 by EddySPalm
Hmm, I just decided to control spindle and feedrate override by means of encoders also, so now I really need to expand upon the original 11 inputs.
PCW, did you mean TB3 in your reply further up here, where you said P3? trying to edit my post to quote you:

PCW post=297580 userid=481
You can use 2 pins on P3 for a MPG, leaving the encoder input free

What would be peoples' preferred way of expanding I/O on the 7i96s? Serial or expansion port? What are the pros and cons to the two? I will utilize it for inputs only, as I am not planning on using up all the outputs on the Mesa card.

Are there RS-422/485 cards which will connect to the serial port and give me access to x number of connection?
I see there are plenty of breakout boards with DB25 connectors which gives me access to the expansion header, but what do you mean that I have to be more careful with them? Are they not opto isolated? If so, are there breakout boards which makes them opto isolated?

So many questions in one post, sorry for the constant questioning without bringing much to the table myself. Hopefully I'll get there some day.
Last edit: 08 Apr 2024 10:01 by EddySPalm.

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08 Apr 2024 14:22 #297815 by EddySPalm
To add to the massive amount of questions, i just had the manual for the AC servos I am considering sent to me by the seller from Aliexpress (Lichuan). Under "Chapter IX MODBUS Communication", I find the following written (see attached picture).
Does this mean I can control all AC servos (1x 1kW for the spindle, plus 2x 200W for X and Z) with only the RS485 interface? Or is it to be intepreted like the RS-485 interface on the drivers is only there to aid setup and tuning by means of a computer?

 
Attachments:

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08 Apr 2024 15:16 #297817 by PCW
A 7I84 or 7I73 are common Serial expansion devices used with the 7I96S

It sound like the drive support Modbus. There is experimental Modbus support
for the 7I96s (and most Mesa cards) but it still has a few known bugs
The following user(s) said Thank You: EddySPalm

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08 Apr 2024 15:35 #297818 by tommylight

Does this mean I can control all AC servos (1x 1kW for the spindle, plus 2x 200W for X and Z) with only the RS485 interface?
 

This is my personal opinion, so take it as such, i would never use RS485 to control a cnc machine, ever.
It works, i have seen it used on industrial machines for automated food and drink lines, but never on a cnc machine to actually control machine axis, it is used on some ATC, vacuum hold downs, some hydraulic stuff, spindle feedback, etc.

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10 Apr 2024 19:53 - 10 Apr 2024 19:54 #297953 by EddySPalm
I will definitely move away from that idea.
You are saying the 7i84 and 7i73 mesa cards are common for expanding on the serial port; is it so that there are not just "generic" bob's to be had all around, line there are for bob's for parallell ports? The reason I'm asking is that purchasing more boards from Mesa is so expensive with shipping and import duties etc. into Norway.
Last edit: 10 Apr 2024 19:54 by EddySPalm.

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10 Apr 2024 20:28 #297956 by PCW
You can use some generic USB pendants

Its also possible to use a generic parallel
pendent connected to P1:

forum.linuxcnc.org/39-pncconf/51733-7i96...etup-in-configurator


 

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