I came across this note that John at Novakon had posted several years ago.
Here is a little more insight of the Torus and Pulsar spindle operation.
The drive signals to the spindle motor from Mach3 are the step and direction signals. There are no translations into a variable DC like is done on the Torus PRO. This means the accuracy of the spindle RPM is within a few RPM. The spindle servo motor has a normal operating RPM range of 1-3000 while the spindle can operate between 1-4500 RPM. The servo driver's internal electronic transmission is used to compensate for the 1.5:1 pulley ratio. You will notice on the servo driver display that it will display an RPM 2/3's of the actual spindle RPM DRO. This is due to the electronic transmission programming.
Mach3's speed DRO will read the actual spindle RPM. Mach3's spindle "steps per" and "rapids" are set for optimum values for use with the servo driver electronic transmission. There are almost infinite combinations of settings that can work between Mach3 and the servo driver to achieve the same result. The parameters chosen allow the spindle to be used for free running and rigid tapping using one transmission ratio.
The Torus has rigid tapping capability. The only difference between the production Pulsars and the Torus spindle is the new Pulsar BOB will switch between two electronic transmissions for spindle "free running" and rigid tapping. This new capability gives us more flexibility with the two operating modes.