Motor Control and Timing
How a Stepper Motor Takes Steps
Understand changing phase currents and full-step/half-step sequences.
You are applying “How a Stepper Motor Takes Steps” to a real system and need the concept, assumptions and verification boundary to stay clear.
See how a two-phase hybrid stepper follows commanded magnetic alignments, and how full-step and half-step current sequences create discrete target positions.
- Select or check first
- Define the required outcome, operating conditions and exact component or system boundary before choosing a part or method.
- Controlling assumption
- Sensors, controller logic, actuator limits, timing, fault response and environmental conditions are defined together.
- Top risk
- Identify windings before applying power. A bipolar driver expects the two wires of each phase to be identified correctly. Mis-pairing leads can prevent rotation and can stress the driver.
- Proof
- Check the exact manufacturer data, units and limits, then verify the result by calculation, measurement or a controlled acceptance test.
Start with the basics Optional foundation before “How a Stepper Motor Takes Steps”
Automation-and-control basics
An automatic system measures a condition, decides what it means and commands an actuator while checking whether the expected result actually happened.
- Sensor
- A sensor converts a physical condition into a signal. Its range, uncertainty, response time, environment and failure behaviour matter as much as its nominal output.
- Controller
- A controller reads inputs, applies logic or a control law and issues outputs. Software cannot correct missing measurements, inadequate hardware authority or unsafe architecture.
- Actuator
- An actuator turns a command into physical action, such as motor torque, valve position or switching. Its real limits depend on load, supply, drive and duty.
- Feedback
- Feedback compares measured behaviour with the desired state so error can be corrected. Open-loop command assumes the action occurred; closed-loop control checks it.
- Fault and safe state
- A fault is an abnormal condition that may invalidate control. The safe response must be defined from the hazard and may require independent hardware, not only software.
How to use this article: Trace one complete chain—physical condition, sensor, signal conditioning, controller, drive, actuator and feedback—then ask how each link can fail.
On this page
A stepper motor moves because its driver changes current in ordered phase windings. Each current combination creates a preferred magnetic alignment. The rotor accelerates toward that alignment, oscillates and settles if available torque and damping are sufficient. The controller therefore commands a sequence of target positions; it does not directly measure that the shaft reached each one.
Phase current creates a moving alignment target
Diagram description
The selected teaching example is a two-phase hybrid motor with a 1.8 degree full step. Motor construction and step angle vary by model.
| State | Phase A | Phase B | What changes |
|---|---|---|---|
| 1 | Positive | Off | Rotor seeks the A-positive stable alignment |
| 2 | Off | Positive | Preferred alignment advances to B-positive |
| 3 | Negative | Off | A polarity reversal advances the field again |
| 4 | Off | Negative | B polarity reversal completes the electrical cycle |
| Repeat | Return to positive | Off | The next mechanical step continues in the same direction |
| Reverse | Use 4, 3, 2, 1 | Reverse order | The target sequence rotates the other way |
The large arrows in the sequence simplify a distributed magnetic field. In a hybrid motor, many stator and rotor teeth produce a small mechanical step from a much larger electrical phase change. The permanent-magnet rotor and toothed geometry establish stable positions; they are why the shaft does not rotate 90 mechanical degrees when the electrical state advances by a quarter cycle.
Nominal full steps per revolution
N_full = 360° / θ_full
A motor rated at 1.8 degrees per full step has 200 commanded full-step positions per revolution. This is command resolution, not guaranteed absolute accuracy, and gearing or mechanics can change the load-side motion.
- N_full
- nominal full-step commands per motor revolution
- θ_full
- rated mechanical full-step angle in degrees
Intermediate current states create half-step targets
Diagram description
The diagram shows equal-magnitude phase commands for teaching. One-phase and two-phase states need not produce equal torque unless the driver adjusts current appropriately.
| Method | Current-state pattern | Practical consequence |
|---|---|---|
| One-phase-on full step | A+, B+, A−, B− | Simple sequence; one phase supplies holding torque at a time |
| Two-phase-on full step | A+B+, A−B+, A−B−, A+B− | Two energized phases create diagonal field targets |
| Basic half step | Alternates one-phase and two-phase states | Twice the commanded positions, but torque can alternate |
| Current-shaped half step | Reduces phase current where both are on | Can make resultant-current magnitude more uniform |
| Microstepping | Many regulated current proportions | Smoother, finer commanded targets; not equal guaranteed shaft increments |
From STEP pulse to winding current
- The controller sets direction and issues a STEP event or sends a position command.
- The driver indexer advances to the next current state.
- Two H-bridges apply the required polarity to phases A and B.
- Current regulation tries to reach the configured phase-current target.
- The magnetic field moves, and the rotor accelerates toward a new stable position.
- Load, inertia, friction, resonance and available current determine whether it settles before the next command.
A correct sequence is necessary, but motion still needs proof
Starting too quickly, accelerating beyond the torque-speed envelope, striking a stop or applying too much load can make the rotor fall out of synchronism. An open-loop driver normally continues counting electrical states, so its internal command can be ahead of the real shaft. Homing, limit checks or an encoder are selected according to the consequence of that uncertainty.
Compare motor families in DC, Stepper and Servo Motors: Which One Fits?. The difference between a command and measured motion is introduced in Open-Loop Commands Versus Real Feedback.
E4 · Educational scene
Explore the decision in three states
Select a state to compare the starting condition, the important change and the evidence needed before acting. The same meaning remains in the static list.
Start
See how a two-phase hybrid stepper follows commanded magnetic alignments, and how full-step and half-step current sequences create discrete target positions.
What changes
Identify windings before applying power. A bipolar driver expects the two wires of each phase to be identified correctly. Mis-pairing leads can prevent rotation and can stress the driver.
Verify
Check the exact manufacturer data, units and limits, then verify the result by calculation, measurement or a controlled acceptance test.
- See how a two-phase hybrid stepper follows commanded magnetic alignments, and how full-step and half-step current sequences create discrete target positions.
- Identify windings before applying power. A bipolar driver expects the two wires of each phase to be identified correctly. Mis-pairing leads can prevent rotation and can stress the driver.
- Check the exact manufacturer data, units and limits, then verify the result by calculation, measurement or a controlled acceptance test.
One-minute questions
Questions to answer before you apply this lesson
What should I select or check first for How a Stepper Motor Takes Steps?
Define the required outcome, operating conditions and exact component or system boundary before choosing a part or method.
Which assumption can change the conclusion?
Sensors, controller logic, actuator limits, timing, fault response and environmental conditions are defined together.
What can go wrong if I copy the example directly?
Identify windings before applying power. A bipolar driver expects the two wires of each phase to be identified correctly. Mis-pairing leads can prevent rotation and can stress the driver.
How do I verify the result in the real system?
Check the exact manufacturer data, units and limits, then verify the result by calculation, measurement or a controlled acceptance test.
Sources and further reading
- Stepper Motor BasicsOriental Motor · 2026-10-13Motor-manufacturer technical guide reviewed for hybrid motor structure, stable alignment, one-phase, two-phase, half-step and microstep excitation concepts.
- DRV8825 Stepper Motor Controller IC DatasheetTexas Instruments · 2026-10-13Semiconductor-manufacturer datasheet reviewed for STEP/DIR indexing, two H-bridges, current regulation and supported step modes.
- AN-323: Microstepping Drive Circuits for Single Supply SystemsAnalog Devices · 2026-10-13Manufacturer application note reviewed for two-phase permanent-magnet torque generation, 90-degree electrical phase separation and rotor stable positions.