All I want is for the machine's rpm to match commanded and actual. I.e. When I command m3 s1800 and measure the actual rpm using a tachometer it matches pretty close, not off by a few hundred rpm.
I understand your frustration but it is not a Mach4 problem and it is not an ESS problem.
The problem lies in whatever connects the PWM output from your ESS to your spindle motor and these are perhaps the areas in which you should be testing.
1) Is the analogue voltage output from your C32 BoB (0 to 10 Volts) linear to the Mach4 commanded S#### ??
2) Does your VFD have linear response (output frequency) when driven by a regulated 0 to 10 Volt standard ??
Tweakie.