Hello all. Thanks for taking up your time to read my post. I have ordered these stepper motors. I asked the seller how many revolutions the motor can achieve in a minute and they answered 43. I calculated (13 + 212/289) * 200 * 43 / 60 to determine how many steps I would need to step in a second to achieve 43 rpm. This results to roughly 1950 steps per second. However, when I try to run the stepper motor with 1950 steps per second, it stalls. It vibrates but doesn't turn. After reducing the steps per second to 1300, the stepper starts moving again. I'm using MK70-1 drivers as the datasheet of http://www.kynix.com/uploadfiles/pdf2286/MK70-1.pdf, set to ignore microstepping and to supply 0,5 A current with 12 V. I'm controlling the driver with an Arduino Mega 2560 and AccelStepper library. Why can't I run it with higher speeds? I've had this problem with other steppers, too. Can anyone help me ? I am very puzzled about this question.