VFD control with low ratio gear selected on the Acorn controller

As noted last time, the motor is being set to the commanded speed, ignoring the 0.167 low gear ratio that I have so cleverly and seamlessly engaged. So now, if I ask for 100rpm spindle speed, the motor itself spins at 100rpm and the spindle then turns at something dumb like 17rpm. I'll need to dig into the manual a bit further to see how to take account of the gear ratio. Clearly the motor would need to be spinning at around 600rpm or so in this example, to achieve the required 100rpm spindle speed in low ratio. 

On the face of it, I could possibly look at the status of the low ratio input (ie parameter #50002) and multiply the magnitude of the VFD control voltage by the gear ratio. That could almost be included in the existing M3 / M4 macros but it all sounds a bit messy. Besides, this issue seems to be taken care of already within the existing controller setup, so why reinvent the wheel, especially as I am no wheelwright of any note.

Having run through the complete list of system configuration parameters, this seems to be the relevant part of the CNC12 manual:

Basically, it looks at PLC inputs 63 and 64 to determine which of the 4 speed ranges the machine has set. The assumption seems to be that the the range will be set manually by the operator and the controller will figure it out from the status of those 2 inputs. No problem in my case, assuming my range selection macro doesn't get its knickers in a twist, up against this PLC logic, although it should only need to look at one of the inputs to figure out what to do.

It's handy that I already have Input 1 (low ratio, variable #50002) and Input 2 (high ratio, variable #50001) reporting the status of the gears. On the face of it, all I need to do is connect up variable #50002 to this "INP64" somehow, then it will see when the low ratio is engaged and compensate for the gear reduction with an appropriate increase in the motor speed. I've posted a query on the forum - let's see what transpires....

The (partial) solution:
The solution is given at the bottom of this page - a PLC source file provided by CNCKeith that allows the wizard to configure the inputs for use with a backgear. That's pretty much what I have, the only difference being that my backgear does not cause reversal of the spindle direction, as it's fully geared, whereas the Bridgeport backgear does, due to the combination of belt and gear reduction stages. So my ratio is 0.167, as opposed to -0.120 or whatever it is on a BP.

Once the revised .SRC file has been pasted into the c:\cncm \WizardResources \Template directory (replacing the original), you run the wizard and reselect Input 1 function as "Backgear", then save, reboot the Acorn etc

It's only a partial solution because the main display screen doesn't report the spindle rpm - it just shows 0 all the time. However, it shows the correct current range (high or low) in the VCP area and my custom M3 and M4 macros continue to work correctly. And this is in the new, super luvvin' 4.16 updated version.

I've now posted again, to see if the rpm (not)display can be fixed.