Servo driver selection

I'm currently working out what to buy to convert my milling machine to Linuxcnc. It is currently fitted with Fanuc red top AC servos

So far I have decided on MESA boards, a 7I77 as I will be using servos. I see this is usually used with a 5I25 board

The 7I76 is described as having a 0-10v output for spindle control, does the 7I77 have this?
Is there an ethernet version of the 5I25 available, or what MESA would I use instead?

Regarding the servos, the Fanuc ones fitted are 48V. 3A stall current.

Servo drive wise I'm not too sure what to do

1) Granite devices. I guess the IONI would drive these motors, but only in torque mode. Plus side they are reasonably priced
2) Granite Argon. Would drive these, and could use velocity mode? Plus side built in power supply, works in velocity mode, downside is cost!! Yes it does everything and drives every mode made, but I only want to drive my motors.
3)MESA 8I20. Not too sure if this would work ok. Would I need the daughter card?

Alternative to the servo drive is to buy some servo drive/motors from china, cost of a motor and servo less that one servo drive. Downside is unknown quality of product. And suitability of the servo for a CNC mill. I'm assuming the Fanuc ones have been designed specifically for machine tool applications?

I like the set up shown on the eusurplus website, and I think that would be a good setup to use, but what with the cost of the Granite Argon drives it does work out quite expensive. Would chinese servo/drives be a better option, or is there a good lower priced AC servo drive available?

Any advice gratefully received

If you want to control Mesa 8i20 drives with a 5i25/6i25 I think I'd suggest a 7i85 plus a Remote Serial card like a 7i84 for io.

Is there any advantage to using a MESA 8I20 servo driver and suitable boards, over using a 7I77 and separate servo drives?

andypugh wrote:

Gatesy wrote:

Is there any advantage to using a MESA 8I20 servo driver and suitable boards, over using a 7I77 and separate servo drives?

No, and in fact the 8i20 is likely to be more trouble to set up than, for example, Fanuc drives matched to the motors.

However, in your situation a small advantage of the 8i20 is that it takes rotor angle as a digital numeric value, so can use the 4-bit Fanuc codes properly (rather than converting inexactly to conventional hall-patterns)

I thought that the whole point of this thread was to help this guy find an alternative to the OE Fanuc drives, that were either too difficult or impossible to make work with Linuxcnc.

Now if the old drives are a workable option, I'd agree that they would almost certainly be the best (and likely most economical option, if they are in his possession.)

Re Fanuc drives

I don't have the fanuc drives, just the actual mill which is fitted with Fanuc red tops. I have used several machines with Fanuc control (Model O) and found it ok, but so outdated even when compared to MACH3

I'd like to steer away from using old Fanuc parts. The reasons being that as it is all Fanuc specific, you have to replace with the same parts, extra axis have to be unlocked, adding in additional functions is impossible, and to repair anything needs a Fanuc engineer. The programme length is minute so CAD/CAM generated programs have to be drip fed.

If I use "off-the-shelf" parts and a modern up to date controller, especially LinuxCNC as it is always being updated, I can do pretty much what I want with the machine. And if a part fails, it can be readily replaced with if not an identical part, but something very similar.

I'm also building another machine so would need another CNC control for that at some point.

The only reason I ask about keeping the Fanuc servos is that the eusurplus wiki shows how to tune a motor, so in theory I should be able to tune the servos myself??? I have no problem removing the Fanuc encoder and fitting a standard type encoder. I was only thinking about keeping them as they are specifically for CNC machines, and I'm assuming they will be a better quality than the cheap chinese servos???

If anyone has used any of the chinese drives/servos and found them to be ok then I wouldn't have a problem using them.

How well does this set up work

Sorry if you miss understood me, I was not implying that you should try to revive the old Fanuc control, just re-use the servo drives and motors with Linuxcnc. However, I am not sure that is possible, and if you don't have them the point is moot, they would probably be to expecive to buy an OE replacement.

Maybe these guys can help you out.
openservodrive.com/fanuc-serial-pulse-co...t-argon-servo-drive/