1. What voltage are you running the ZM-2H606 from? It needs to be several times higher than the stepper motor coil voltage to get torque at high speeds.
2. Are you accelerating the motor smoothly? You can't get a stepper motor to move at high speed instantaneously from rest because of the rotor inertia.
2. Are you accelerating the motor smoothly? You can't get a stepper motor to move at high speed instantaneously from rest because of the rotor inertia.