Speed up a stepper motor

which mean to say that,it is independent on the driver is it?no matter how good your driver is, it still cannot exceed the torque limit of the motor?

There is no hard "torque limit" in an electric motor. You can likely exceed the rated current of the motor and produce torque higher than what is listed in the datasheet. You will begin to get diminshing returns due to field saturation in the magnets. Keep increasing the current and you could eventually damage the magnets.

Torque is related to the current flowing through the windings of the motor. More current = more field. More field = more torque.

Physical limits are hard to bypass... I point out steppers in particular because they are pretty darned reliant on magnetics. As far as I know, if you disassemble any stepper motor and pull the rotor (with magnets) out of the housing, that'll damage the magnets. If you want more info, search for "stepper demagnetization".

This person has a useful picture of torque vs speed vs current for some stepper - notice that torque drops off pretty quickly versus speed - regardless of the current. I think this is pretty typical for steppers.

**broken link removed**

now i think of want to drive the bipolar motor and i think i can no longer use this UCN5804B to drive them,as mention by phalanx and james the A3984 and A3977 both are DMOS microstepping Driver with translator,But can i know how to hook this to my microcontroller so that i can easily drive them?Thanks.

Just read the data sheets. All the motor controllers made by Allegro Microsystems are pretty easy to interface with.

Ok,i'll read through the datasheet very carefully,hope the interfacing is simpler than this UCN5804B ,one of the reason i feel it is harder is because the number of pin it goes there =.="

u use assembly language for the coding or c language?i already done to make the various speed of the stepper motor by using assembly language.but now..i want to change the code to c languange...

i think you can build this circut and control the speed with switches....i tried it before , it works very well

https://www.imagesco.com/articles/picstepper/04.html