Working principle
A stepper motor divides a full revolution into a fixed number of equal steps and moves exactly one step for each pulse the driver sends. A hybrid stepper combines a toothed permanent-magnet rotor with a toothed stator, producing a common step angle of 1.8 degrees, or 200 steps per revolution. Because each pulse corresponds to a known mechanical angle, position is controlled by counting pulses — no encoder and no feedback loop are required.
Holding torque and microstepping
With the windings energised but no pulses arriving, a stepper actively holds its position; the torque it can resist before slipping a tooth is the holding torque, and it is the headline figure on any stepper datasheet. Driving the two phases with proportioned currents rather than full on/off lets the driver place the rotor between full steps. This microstepping smooths motion and reduces resonance, though the accuracy of each microstep is far poorer than the accuracy of a full step.
Speed, chopper drives and lost steps
Winding inductance is what limits stepper speed: the faster you pulse, the less time current has to build up, so torque falls off as step rate rises. Chopper drivers fight this by running from a supply many times the rated phase voltage while regulating current with fast switching, which pushes the corner speed much higher. If the load ever demands more torque than is available at that speed the motor silently misses steps, and because the system is open-loop the controller never finds out.
Where it is used
Stepper motors are the standard actuator for open-loop positioning: 3D printers, CNC machines and laser cutters, flatbed scanners and printers, camera and telescope mounts, syringe pumps and laboratory automation. They are cheap, precise and need no feedback hardware, but they draw full current even at standstill, they are inefficient at high speed, and any serious risk of lost steps pushes the design toward a closed-loop servo instead.