Dc servo motor control

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!     

 i use the 7i40hv for similar motors on my little cnc. i saw that the differential encoder has to be okay

There are 4 or 5 similar machines already working with LinuXCNC daily:
forum.linuxcnc.org/show-your-stuff/34986...nuxcnc-and-proma-thc

forum.linuxcnc.org/38-general-linuxcnc-q...rade-project?start=0

Do you still have the original DC servo controllers ?

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.

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

tommylight wrote:

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? 
 

andypugh wrote:

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

Yes they are.

andypugh wrote:

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.

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.

    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.