Calculating speed-torque curve for stepper motor

[Emil]

I'm making a spreadsheet to estimate speed-torque curves for stepper motors when used with a current limiting driver.

I got the formulas from the spreadsheet in this post: http://www.mycncuk.com/threads/1524-What-size-stepper-motor-do-I-need

Corner speed = 191 * Supply voltage / (Rated current * Winding inductance)
Torque below corner speed = (Holding toque * Set phase current / (sqrt(2) * Winding inductance) ) - Detent torque
Torque above corner speed = ( (Torque below corner speed * Corner speed) / Speed ) - Detent torque

Are these formulas correct / reasonable approximations?

I'm particuarly uncertain about the corner speed formula, because I don't know where 191 comes from and the calculated corner speed is higher than what I get from speed-torque curves from stepper manufacturers.

Coil resistance is also ignored, this seems reasonable as long as the driver is limiting the current, which I think will only be the case below corner speed?


Emil