Performance difference between Mesa 6i24 / 6i25?

Hello,

I'm looking at retrofitting a small lathe with linuxcnc using Mesa boards, the lathe has fanuc red cap servos so I intend to drive these using 8i20 drives, I understand that to control the servos in torque mode needs a fast servo loop, to this end is there any performance difference between using either the 6i25 card or the 6i24-25?

The 6i24-25 has more capacity for bigger 50 pin daughter cards, but I've worked out what I need and it should be comfortable with the 6i25 with a 7i85 for encoder input and serial connection to the 8i20 drives and additional serial i/o board, the second port would have a 7i76 for general i/o and spindle analog control.

The 6i25 setup looks the best choice and the cheapest but Is there any performance benefit to using 6i24-25 or will the PC be the limiting factor for the max servo loop frequency?

Any comments or info much appreciated

I don't think there would be any difference in thread performance. That is more dependent on the PC.

I think I would be considering the 6i24 + 7i44. (This is what I have driving the 8i20s in my lathe, but I also needed the 7i49 resolver card, so had no choice about using a 50-pin card)

Have you checked that smart-serial on the 7i85 is possible? (It certainly won't be as neat to wire as with the 7i44 or 7i74)

Thanks for the comments guys,

I've not specifically asked if the 7i85 supports smart serial but the manual for it does say that it can easily interface to Mesa serial i/o devices including the 8i20 drive. For sure it wouldn't be as neat as having both ends just plug in with a cat5/6 cable.

Which mesa card can achieve faster servo thread
5i24 vs 6i24 vs 7i80hd ?

You can typically run a servo thread faster on a PCI or PCIE card than a Ethernet card

You can typically run a Ethernet card at about 4 KHZ with a fast host PC
The same host will typically run up to say 8 KHz with a PCI/PCIE card

8 KHz is probably not practical with most sserial cards however. 4 KHz is a typical upper limit when you have sserial cards.