Dc servo motor control

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21 Mar 2022 10:20 #237898 by Joeymcc
Hi,

I am looking at retrofitting an year 2000 esab suprarex gantry with linux cnx and mesa boards. The old dc servos are still on the machine, I am trying to decide if i should use the or upgrade to ac servos. What control options will I have with the existing servos using mesa hardware? I am not familiar with this dc servo setup, i have built previous machines using ethir ac servos or steppers. Any help welcome!     
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21 Mar 2022 11:07 #237899 by billykid
Replied by billykid on topic Dc servo motor control
 i use the 7i40hv for similar motors on my little cnc. i saw that the differential encoder has to be okay

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21 Mar 2022 11:10 - 21 Mar 2022 11:11 #237900 by tommylight
Last edit: 21 Mar 2022 11:11 by tommylight. Reason: Link

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21 Mar 2022 12:01 #237903 by HansU
Replied by HansU on topic Dc servo motor control
Do you still have the original DC servo controllers ?

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21 Mar 2022 12:47 #237909 by andypugh
Replied by andypugh on topic Dc servo motor control
You could also look at the Pico PPMC (which requires a parallel port, though used as a communications bus rather than bit-banging pins)

The answer will depend on whether you still have the DC servo drives, though.

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21 Mar 2022 13:48 #237915 by tommylight
Replied by tommylight on topic Dc servo motor control
Picture with those green round things, that is the servo drive.

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21 Mar 2022 14:25 #237922 by andypugh
Replied by andypugh on topic Dc servo motor control

Picture with those green round things, that is the servo drive.

Ah, yes. I overlooked that. 

I guess the question then becomes whether they work or not.

I guess that they are analogue-voltage controlled velocity-mode servos? I am confused by the second photo, is that stacked motors or a very large tachometer? 
 

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21 Mar 2022 14:36 #237925 by tommylight
Replied by tommylight on topic Dc servo motor control

I guess that they are analogue-voltage controlled velocity-mode servos?

Yes they are.

I am confused by the second photo, is that stacked motors or a very large tachometer?

Those are very small motors! :) So the tacho and encoder look huge on them. Outer diameter difference between motor and tacho/encoder lid is about 2 CM.

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21 Mar 2022 15:17 #237932 by andypugh
Replied by andypugh on topic Dc servo motor control
To answer the original question, a common choice for a DC servo machine is the 5i25/6i25 PCI/PCIe card and a 7i77.

Alternatively the 7i97 is am ethernet-interfaced all-in-one for around the same price.

Both may be somewhat overkill for this application.

An alternative would be to use cards from the the 50-pin header card family[1], with a 5i24 or 7i93 and the 7i33TA (but then you would probably need another breakout for GPIO)

[1] There are two main families of Mesa cards. Some use a 50-pin header, and these go back to the 5i20 which was the first to be supported by LinuxCNC. Then the 5i25 came along as a "souped-up" parallel port with a DB25 connector.
Then, on top of that, there are all the smart-serial interfaced daughter cards, which hook together with CAT5 cables.

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21 Mar 2022 19:14 #237945 by Joeymcc
Replied by Joeymcc on topic Dc servo motor control
    Thanks for the help everyone,  i have done a few builds on mach4 but want to try something else, had some problems with random stops in mach4. Im amazed at the projects already im this forum, info has been otherwise difficult to find on the internet.Linux is completely new to me as is the dc servo setup, but Im sure with research i will get there.  
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