Help with selecting hardware for CNC retrofit

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16 Sep 2021 09:39 #220781 by Norrby
Hello!

I am newbie on CNC machines but somehow I managed to buy a huge an old plasma CNC machine  (Vanad Kompakt 1500 from 2001 with MEFI 836 CNC control). It works now but it was no electrical documentation for it so my plan is to exchange control system for it.
As it is now I'd would like to keep the servos, tachometers, encoders to keep the costs down.
It has double PMDC motors for X-axis, one PMDC for Y-axis. The Z:axis has a simple car wiper motor.
The PMDC motors is 24VDC,5A,80W and have separate tachometers and encoders (TTL Quadrature).
(The plasmaburner is not working so I'm planning to rebuild the machine to a milling machine so I will mount a spindle motor later on.)
Right now my choice is to go for LinuxCNC and a Mesa card like the 7i96E/7i96 but I am not sure what motor driver card I should use..
Would really appreciate any tip on hardware that I should go for.

Thanks in advance 
Pär
 
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16 Sep 2021 09:58 #220785 by tommylight
If the drives are working first find out how they are controled, chances are they use analog +-10V, so for that a Mesa 7i97 should do, or a combo of one Mesa 5i25 or 6i25 or 7i92 with a Mesa 7i77.
Do a search for Esab UltraRex there are several retrofits here on the forum to get an idea of what is involved.
Having schematics saves a lot of time.

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16 Sep 2021 11:48 #220788 by Norrby
Thank you for quick reply!
Ok I will try the measure them up and see if I can figure out how the drives are wired and functions and hopefully be able to use them as well.
The following user(s) said Thank You: tommylight

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16 Sep 2021 11:51 #220789 by tommylight
Take a lot of pictures and upload them here on the forum (not on 3rd party sites), we are pretty good at figuring things out from pictures, especially connectors, boards, tags, etc.

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17 Sep 2021 15:06 #220909 by Norrby
I've taken some photos of the motor drivers and luckily when remove the clips it was labeled on the the card so that made it a little bit easier 
Started the machine and a found out that one of the X-axis drivers isn't working so it only drives with one motor at the time..
One of the fuses on the driver card is blown and it seems to be some shortage that I haven't been able to find which component that is faulty so I guess a need to find a motor driver card for that motor. Grateful for any tip for a good driver card.

The encoder cables are connected directly to the PC and the tacho are wired to the driver card.
When measuring "SYMETRICKY VSTUP + & - " (see picture Drivercard labels) I get -3VDC to 3VDC. I have only managed to manually jog the motors and there is a speed settings in manual mode that goes from 0-3, so I'm not sure if it possible to drive the motors with -10V:10V.
Maybe it's speed limited in manual mode and that is why it only is -3V/3V?
Have a Raspberry pi 4 with LinuxCNC on so I've thinking of buying 7i92M and a 7i77. Is that an ok setup or should I get hold of a PC with parallel port and go with 5i25 and a 7i77?
 
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17 Sep 2021 17:45 #220929 by tommylight
Symetricky Vstup =  symmetrical input.
How exactly did you measure the input?

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17 Sep 2021 21:02 #220948 by Norrby
Measured DC voltage over "+" and "-" see attached picture.
Also same voltage over "+" and ground "GND".
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17 Sep 2021 21:18 #220949 by tommylight
- and gnd ? Always 0 ?

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17 Sep 2021 21:30 #220950 by Norrby
Yes, no voltage difference over "-" and "gnd" when I run the motor.
I will check the motorspeed tomorrow when it runs on max (3V) and see if it comes up to 2000rpm/min as the motordata says.

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17 Sep 2021 21:42 #220951 by tommylight
Nice, so it is an analog drive with +-5V or +-10V , so a Mesa 7i92 with Mesa 7i77 should do just fine or go for the Mesa 7i97 as it has both on the same board.
BTW, if you go the Mesa 5i25 or Mesa 6i25 with Mesa 7i77 route, there is no need for a parallel port.

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