Retrofitting Fadal VMC15-XT w/Mesa

Well, you did a lot of reading, utmost respect, but now you find yourself in the positions of knowing fragments of stuff, so to keep from making any hiccups just keep asking.
Find info on the resolvers, Mesa has also something for most of them.
If the servo amps still work, use them, till the first one dies, then change.
Old servo amps are most probably analog controlled, most new ones can do analog and step/dir, most old ones are velocity mode meaning they have a tacho that is also wired to the drives, new ones do not need a tahco.
Mesa 7i95T is a step/dir control mode device, with it's own FPGA on board, so it can not be used with older analog drives, hence the need for 7i83, and connects to PC through Ethernet.
See where this is heading?
That combo provides analog and step/dir control, so you can use it with existing drives and analog control wired to 7i83 till one fails, then get 3 new drives for the price of an old one, and wire the new ones to 7i95T OR to 7i83 depending on what you choose as control type.
Sinking and sourcing outputs in general:
Sinking outputs = the outputs go low to 0V or ground when active
Sourcing outputs = the outputs send +V when active
+V is 5V or 12V or 24V or whatever the board is supplied with minus a small drop of usually 0.6V

zerobalance wrote:

So the best option seems to be 7i95T, mated to a 7i83 as you suggested. 6 output might be enough, but I bet I will have to add a daughter board to control everything I need.

I did not, PCW did suggest that combo, i did the 7i96S with 7i85 and 7i83, so they do the same thing and easier to use/wire, the PCW's combo, that is.
You can add as many inputs and outputs as you like, or any combination of them, see 7i70, 7i71, 7i72 and 7i84, very easy to wire and no programing, except editing the hal file to add the pins.
7i95 has 2 of SSerial on board, if i am not mistaken been a year that i installed it and it is in use at a clients shop, not sure if 7i95T has also 2, leme check... yup it does, so you can have 7i83 and 7i84 (using a single LAN cable cut in half for both ) adding another 32 inputs and 16 outputs for not much money.
Upfront, sorry about the money thing, but any Mesa card i have bough ( a lot) cost me at least twice the listed price due to where i live, and i gladly pay it, just the reliability makes me sleep good at night, having the best support on earth is just a bonus.