0.9 vs 1.8 steppers

Morning!

With steppers I am aware that for a given stepper motor the greater the lag from the target position the greater the torque trying to reduce this lag. I have also heard 0.9 steppers have lower rated torque than 1.8 steppers and with either case if the lag exceeds two physical steps the torque will invert and the stepper will loose at least 4 physical steps.

My question is how do similarly sized 1.8 and 0.9 steppers compare torque wise for a given lag. Perhaps 0.9 or 0.45 degrees, well within what is likely to cause the 0.9 degree stepper to loose steps.

If the holding torque were equal, the 0.9deg motor would provide twice the torque per unit lag angle, for small amounts of lag angle. In practice a 0.9deg motor will have a little less holding torque than a similar 1.8deg motor, but well over 50% of that torque. So the 0.9deg motor wins.

This assumes that you don't reach the speed at which the voltage needed to drive the requested current through the motor exceeds the supply voltage to the driver. That speed will be reached sooner on a 0.9deg motor than on a similarly wound 1.8deg motor.

Edited 3 time(s). Last edit at 05/01/2019 12:36PM by dc42.

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Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].