Mesa 7i77 config for two spindles

Have a mesa 7i77 setup on my bridgeport cnc with a vfd controlled spindle. I just ordered a 24,000 rpm 1.5kw air cooled spindle with matching Hungyang VFD for use as a auxillary spindle for engraving and other such high speed uses. I will put the high speed spindle on as needed and run a separate config for each spindle setup.

What I have in mind is to parallel the 0-10V speed control output from the mesa 7i77 to BOTH vfd's. I am making the assumption that the 0-10V speed control input on most vfd's is a high impedance input and my proposal would not be a issue.

I will use the standard I/O lines for "run fwd" , "run rev" to each vfd, no sharing of lines/signals there. Only one VFD would be given a run command, the unused VFD would sit powered on but without a run command. I will have a separate config launcher for each spindle setup each with appropriate HAL and INI files for that spindle.

Is this a reasonable config idea? Alternately, what about using a unused servo channels 0-10V output and configuring it for the second spindle via some HAL and INI config lines?

Yes but VFD's internal 10V source is not used with mesa 7i77, the 0-10V is sourced from the mesa board.

The hungyang VFD does indeed have RS485 control capability and I have been looking at that. It seems like the easiest/best approach for my dual spindle setup. An added plus is that there appears to be a published component for linuxcnc to control hungyang VFD's with RS485, so most of the hard work is already done !

From what I have read, a USB to RS485 converter is the method used for the physical wiring interface.