Stepper motors and linear scale closed loop setup?

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17 Nov 2020 10:51 #189584 by Muzzer
Rightly or wrongly, I plan to convert my Colchester Bantam to CNC using step/dir servos, ground ballscrews etc. I blame lockdown.

I will take every sensible measure to minimise backlash but plan to integrate linear scales on X and Z, as it would seem rude not to.

I have a 5i25 / 7i76 combo but believe I would be short on encoder inputs. I'd need 3, including a spindle encoder. Possibly 5 if I were to feed back from the servo drive encoders too, although I don't imagine that would be particularly worthwhile. What's best for me here - can I add a second board alongside the 7i76 or is there a better solution that is cost effective?

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17 Nov 2020 11:27 #189585 by tommylight
Have a look at Mesa 7i85 or 7i85S, should have 4 encoder inputs and should be usable with 7i76.
Not sure as i never used a 7i85 or 7i76, for some strange reason, should have since i had over 40 of Mesa boards ! :blush:

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18 Nov 2020 15:17 #189678 by Muzzer
Looks as if the 7i85 connects to the 7i76 using RS-422 via one of the on board headers? I hope so, as I'm expecting to receive one tomorrow. I notice that the 7i76e has a couple of ribbon cable headers for expansion whereas the original 7i76 (like mine) doesn't, while the 7i76 manual shows the 7i76e. Bit confusing.

Tangential question - what are the preferred GUIs for lathe use? I see Gmoccapy has a lathe mode but TBH it doesn't seem as slick as the mill version which I'm guessing was the original target.

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18 Nov 2020 15:23 #189679 by PCW
The 7I85 connects to a FPGA card not the 7I76

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18 Nov 2020 15:55 #189683 by Muzzer
Hmm. So I have a 5i25 and 7i76. I just bought a 7i85 - am I missing a critical component?

From tommylight's response, I thought this was a compatible board. Seems not - what to do?

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18 Nov 2020 16:21 #189688 by PCW
You would need a cable to connect from the 5I25 to the 7I85

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18 Nov 2020 16:31 #189690 by Muzzer
I was guessing so - but as I only have one 5i25 and would appear to need it for the 7i76 to drive my servos, I'm wondering where that leaves me. The motherboard only has one PCI slot as it is.

So do I "put the 7i76 and 7i85 aside" (possibly the 5i25 too) and spend more beer tokens on a 7i96 or similar? I would presumably be best off to go for an ethernet connection these days.

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18 Nov 2020 16:32 #189691 by PCW
The 5I25 has 2 I/O connectors, one is used for the 7I76 (P3) and the other (P2) would be used by the 7I85

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18 Nov 2020 18:06 #189699 by tommylight

Hmm. So I have a 5i25 and 7i76. I just bought a 7i85 - am I missing a critical component?

From tommylight's response, I thought this was a compatible board. Seems not - what to do?

PCW explained already, but just in case:
5i25 will work with 7i76 AND 7i85, you do need a 26 pin header to DB25 cable and another DB25 to DB25 or parallel port cable.
This is the header, might find it in some PC it was widely used in some of them :
eusurplus.com/index.php?route=product/category&path=59_63
First and third OR second and third, depending on the PCI slot size.

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18 Nov 2020 21:22 - 18 Nov 2020 21:30 #189732 by chris@cnc
Hi , i have the 7i76E + 7i85s + 7i85 + 7i84
Bit file is in standard an works pretty well :)
Attachments:
Last edit: 18 Nov 2020 21:30 by chris@cnc.

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