thankx for the reply SABorn,
but the software is not the problem. i checked the speed of stepper motor from EMC2, Kcam, Mach3, and i found that the software does not make any difference. if i tell the software to run motor at 170 or 1500 rpm, then after reaching at 150 the motor stars only vibrating. It clearly means that (i hope that) the driver is not giving enough time to move the motor from one step to other.
but i dont know how to solve this problem. i tried to increase the power for the motors from 24VDC to 36VDC, but it burned up L298N in 0.5 second. i also tried to run the motor at 0.5,0.9,1.2,2.0 AMP (per phase) but id does not make much difference. so now i think that there is some problem with the chopper rate.
i hope that now you do understand my problem. and you can always tell me abut any other good bipolar stepper motor driver which i can make by my self.
thankx for reading.
and yes i posted the same question in 2 forums bcoz i didn't knew that which one is the correct forum for my question.