Ok so many of us have been looking into brushless motors from the RC industry to drive our high speed spindles. I was thinking, if you guys could implement the control scheme to drive a brushless motor Electronic Speed Control or ESC. What this ESC needs to run is a modified version of a PWM square wave. Its a 1-2ms pulse every 20ms at 5v. So 1-2ms pulse @ 50Hz (0 rpm @ 1ms, full rpm @ 2ms).
-____-____-____ <---- 1ms --___--___--___ <---- 2ms
Also have an arming feature built in since some have a safety feature where they need to have the "throttle" at a certain pulse rate ( 1.5ms or whatever) for a second or so when you first turn it on ( just have a box to enter a wait period, and ms pulse length). So if mach3 reads an m3 command, it will activate a relay, turning on the spindle ESC. I guess this could be tied into the Dwell feature of mach3... not sure...
Right now I getting help programming an arduino to take mach3's normal square wave and convert it to this control scheme. But if you can do this, this extra electronics won't be needed.