Hi Voicecoil,

Yeah I wondered that but seems to be similar with standard/open-loop steppers from what I can tell. As an example there's this motor that Zapp sells: sy85sth65-5904b
 (5.9A, 1.7mH, 200steps/rev, bipolar)

The graph on the spec sheet suggests the motor is good up to 8000 pulses per second at half step which is 1200RPM on the shaft at 110Vac. (I assumed the equivalent DC supply voltage to be 77.78V - the RMS value of 110Vac)

But the result of calculating the maximum RPM via the link in my first post (based on the equation T=LI/V (multiplied by 4 for Bipolar Series)) gives a theoretical maximum spindle speed of 582RPM at 77.78V - less than half of the RPM the graph suggests is possible with the motor.

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I guess the crux of my question is this: how can stepper motors be driven faster than 'should' be possible based on the speed limit imposed by the time it takes for an Electromagnetic field to build and then dissipate in the coil?

Perhaps the coil isn't fully charged or discharged at higher speeds, operating somewhere between?