Virtual tach for Fanuc DC drives

I'm looking at another retrofit but this lathe has fanuc DC 6047 drives. Currently the drives rely on a tach signal generated by the controller from the encoder.

Can I scale the encoder velocity to get 6v/1000RPM and output it thru an empty analog output on the 7i77?
The VCMD is 7v/1000Rpm so the 10v limit would run out there first

So
Encoder 0 would still connect to the PID and then output on analog out 0 to the drive VCMD
Encoder 0 velocity would be scaled and output on analog out 1 to the velocity feedback of the drive

Will the velocity feedback be fast enough to keep the drive happy?

Thanks
Cory

Maybe...

This has been done successfully with other systems
There's currently someone on the LinucCNC mailing list trying
this (with Fanuc drives) but having stability issues, though it may
or may not be related to the velocity feedback

I think its certainly worth a try, you may need to run the servo thread faster
to minimise the phase lag (say 4 KHz or so)