Everything over modbus is at modbus speed, no matter how fast the brain is.

But if you were using a brain for somthing that did not involve modbus, you would get full brain speed . . . . whatever that may be.

Incidentally, Mr Hood, you never did say how you stop your motors after killing power. Inquiring mindes want to know. My setups are not much different than your except for brand.

My drives have internal shunt circuitry so that is one part of it, the spindle motors have brakes, the axis have friction, when I hit E-Stop things stop dead, in fact I dont like doing an E-Stop when things are moving at 10m/min on the lathe, 500Kg plus stopping dead puts strain on things, but sometimes it has to be done

 
Hood

Brakes are easy enough to understand. I have brake motors on some axis, some not. Not a conscious decision, just whatever motors were available at the time. My spindle has a fairly stout disk brake that I added using the caliper from the 4th axis . . .  a bit of overkill there. It is solenoid driven pneumatic, but I do not have it set up as sailsafe. Probably be a god idea to do that.

Since you mention shunting in the drive, I will assume that you do not cut power between the drive and the motor.

On the Mistu, you can feed the electronics separately from the power side of the drive so you can remove power and the drive still stay 'awake' and can stop the motors, in which case, cutting the power would be for safety and not as the sole means of stopping the motors. I think that is the smart way to set it up.

The Mistu has separately configurable decel on loss of power and also configurable behavior of power up after a power loss. All very good features.

We are some distance off topic here, so I'll get back to work now. Nice chatting with you again.

No, motor to drive is always connected and yes my drives have standby power for the logic. Another thing you may want to look at is to see if you have fwd and reverse overtravel inputs.

Hood

Yes, there are limits in the drive. There is probably a 'bring me coffee and toast' command  ,  . . .  however,  I don't even have limit switches on the mill yet 

I built the mill for a specific project and only had time to get it finished enough to do the project. Just too busy to finish it out. When I do get some time for my own stuff, I would probably spend it building my new 'permanent' mill. There are stacks of steel and ball screws and slides all over the place, I just need a stack of time.

I take it you use the limits in the drives rather than MACH. What is the advantage?  I'm thinking about messing with a linear encoder. Not sure if I can do that with the Mistu.
 

What I am getting at is you can wire an input up and configure as both Fwd and Rev over travels and have that in the E-Stop string and your drives should stop instantly. It may not be possible on your drives to set multiple functions to one input but on mine it is. Would also have to make sure that you have shunt circuitry in your drives, so they can dump to the shunts.
Hood