Looking for different communication possibilities.

use mesa 7i77 ... +/-10V and enc .... modbus is never rtai ... all plc have modbus module .. but modbus is not a rt protocol. .... nobody will certify a safety chain based on Modbus (for shure I'm in UE) .... and I have not seen around many security modules canbus ... why? Other question for you: if it is not good for security can be good to drive a motor? There is some difference between make sure to run a thing and make sure it's a sure thing.
Apologize if I seem rude ... the fact is that I do not speak English well.


Regards
giorgio

Grazie Giorgio, tranquillo. I think we speak the same english. I agree on the modbus.
Other problem: winches can be 20-30mt from the pc, and the same distance one to the other.. so i think i should go ethernet or rs485 to mesa analog drivers, which are each close to its motor. What about that?

ok dab77 .... not understand very well your problem about distances .... probabily because I'm not familiar with all winches mechanical design. With 7i77 I make cartesian paletizer with 45mt of cable for "a" axis, 40mt for "y" , 35mt for "z" & 28mt for "x" ..... motor x-z axis of 2.5kw, y 1000w & a 200w. For electrical part I think winches and paletizing robot (cartesian type) is not so different.... x = 5500mm Z = 3400mm Y = 2400 mm all to 60mt/min max vel ....

If you use ethernet/serial mesa cards, you must make an electrical box near every motor ... I understand well your ideas?
In these case consider the difference between cable cost and electrical box ... I think cable is better. If your spidercam is a spider delta robot I think cable is suitable. If your spidercam have usual late/mill velocity (15mt/min max) you can use for shure ethernet cable and mesa ethernet or serial card. I not love the surprise, and in my experience EtherCAT also suffer if you fly too many axes with high dynamics. I talk about close ethercat not open version. ....
Now I work of imagination and imagine that you have many inputs and outputs associated with each axis .... pressure, tension cables, brake winch, temperature control and other ... In these case you have 3 option: 1) your ideas (mesa ethernet: motion control + io near interesting point) ... 2) You can have 3 cables for motion control (motor power, encoder cable cable) + can bus/ethercat for remote plc io (+power cable for remote io) .... 3) as option 2) but with multipolar cable or bus cable for junction box for io (no remote plc module but juntion box). These structure request Lcnc + pc for motion control and HMI & std plc for io control + emergency chain. More respectful of the regulations for industrial environment than use only Lcnc for pilot all. Plc has its certification, and Nobody care who pilot servomotor if the emergency controls and safety are related to the safety plc.

But other can have ideas better than mine.

regards
Giorgio

Winch? We are talking about overhead cranes right?
Then usualy they are for all intents and purposes a 3 axis cnc and they have the same layout, long non moving rails on both sides ( call it Y axis ), a gantry that moves on those rails ( call it X axis ), and the winch that is moving on that gantry with the up/down part.
If that is the case, the controll box is always mounted on one side of that gantry. I would put the control box next to that electrical box as all the cabling will go from there. In that box should be relays or servo drives with Mesa boards ( if you choose Mesa, i know i would ), so i would have to add a single ethernet cable up to the control box. Cat6 ethernet cables can go up to 100 meters easily, so can shielded Cat5 ( named STP or shielded twisted pair ). There is also the posibilty of lowering the singal speed through ethernet cable as all network cards can be set to work in all these modes: 10 Mb half duplex, 10 Mb full duplex, 100 Mb half duplex, 100 Mb full duplex, and new ones at 1000 Mb half and full duplex.
For Mesa boards the half duplex can not be used, but full duplex will most probably work properly even at 10Mbit.
These seting are awailable and functional in most Linux distros on network managers, can also be set through terminal in any Linux.
This is the most eficient way of doing it as the cables will remain short.

dab77 wrote: winches can be 20-30mt from the pc,

I think 20m is too far to transfer an analogue velocity signal. I think closing the loop at the drive and sending absolute position on RS485 or similar is the best plan.

My ideas was closing loop in drive, using Lcnc as 2th loop and use 20mt of power and encoder cable .... in these case pc and electrical box in the same box.
Obviusly 20mt of analogue signal cable is too much...

regards
Giorgio