Motor Control and Timing
Microstepping, Speed and Torque Limits
Learn how microsteps are created and why performance changes with speed.
You need to size or verify a real system using “Microstepping, Speed and Torque Limits”, with units, duty and limits that match the application.
Understand sine-cosine phase-current commands, why microstep resolution is not accuracy, and how winding dynamics, speed and acceleration consume stepper torque margin.
- Select or check first
- Small command increments have small incremental torque. Near a commanded equilibrium, the torque change associated with one fine microstep can be much smaller than full-step holding torque.
- Controlling assumption
- Sensors, controller logic, actuator limits, timing, fault response and environmental conditions are defined together.
- Top risk
- More supply voltage requires a regulating driver and correct ratings. Do not connect a low-voltage stepper directly to a higher supply merely to gain speed. A suitable current-regulating driver, configured current limit, insulation rating, overvoltage strategy and thermal design are required.
- 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 “Microstepping, Speed and Torque Limits”
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.
Microstepping asks the driver for many intermediate ratios of phase-A and phase-B current instead of only full-on, off or reversed states. That rotates the commanded magnetic field in smaller increments and usually reduces low-speed vibration and noise. It does not divide every real shaft step into perfectly equal pieces. Load torque, friction, detent torque, motor geometry, current-regulation error and production tolerances all shift the actual resting positions.
Two controlled currents create one target vector
Diagram description
Eight increments per full step are illustrative. Real drivers offer specific modes, current tables and regulation errors documented by their manufacturers.
Idealized two-phase current commands
I_A = I_pk sin(φ), I_B = I_pk cos(φ)
The ideal pair keeps the magnitude of the current-command vector constant because sine squared plus cosine squared equals one. A real driver uses discrete lookup values, current sensing and switching regulation, while the motor's magnetic field and load determine the resulting shaft position.
- I_A
- commanded current in phase A
- I_B
- commanded current in phase B
- I_pk
- configured peak phase-current scale
- φ
- electrical command angle
| Term | What it says | What it does not prove |
|---|---|---|
| Full-step angle | Nominal spacing of full-step equilibria | Loaded absolute position |
| Microstep subdivision | Number of command states within a full step | Equal mechanical increments |
| Driver current setting | Target current scale under stated conditions | Actual current at every speed and supply |
| Holding torque | Static torque under specified excitation | Torque available during acceleration |
| Repeatability | Ability to return under a defined test | Absolute accuracy across all loads and directions |
| Encoder resolution | Measurement increments | Closed-loop stability or machine accuracy |
Speed leaves less time for phase current to reach its target
Diagram description
The curves are qualitative and contain no universal torque, speed or time values. Inertia, resonance, voltage, current regulation and temperature change the envelope.
Winding electrical time constant
τ_e = L / R
This simple resistance-inductance measure helps explain why current cannot change instantly. A chopper drive uses supply-voltage headroom and switching regulation to build and decay current faster than a simple resistor-fed winding, but supply, driver and motor voltage limits still apply. Back electromotive force at speed further reduces current-changing headroom.
- τ_e
- winding electrical time constant in seconds
- L
- phase inductance in henries under the stated test condition
- R
- phase resistance in ohms at the relevant temperature
| Factor | Why margin changes | How to verify |
|---|---|---|
| Speed | Shorter dwell and back EMF reduce achieved current | Motor-driver torque-speed curve at intended supply |
| Acceleration | Load and rotor inertia require additional torque | Move-profile test with worst credible inertia |
| Friction and process load | They consume torque before acceleration begins | Measure across temperature, wear and direction |
| Resonance | Mechanical oscillation can destabilize synchronism | Sweep speed and acceleration; test damping or microstep settings |
| Supply and wiring | Voltage droop and cable loss reduce driver headroom | Log bus voltage and phase current during moves |
| Temperature | Winding resistance and driver thermal limits change | Hot-condition endurance and fault test |
A defensible stepper operating-point test
- Use the exact motor, driver, supply voltage, cable and mechanical transmission.
- Set phase current within both motor and driver limits and verify cooling.
- Apply the maximum credible load, inertia and opposing force.
- Test the complete acceleration, speed, reversal and stopping profile.
- Exercise temperature, supply tolerance and resonance-prone speed regions.
- Measure actual load position or use a repeatable reference; command counts alone are not evidence.
- Derate from the first failure boundary by a documented margin and repeat across representative units.
Read a complete motor curve with Understanding Motor Torque-Speed Curves, then include inertia and duty in Duty Cycle, RMS Torque and Reflected Inertia.
One-minute questions
Questions to answer before you apply this lesson
What should I select or check first for Microstepping, Speed and Torque Limits?
Small command increments have small incremental torque. Near a commanded equilibrium, the torque change associated with one fine microstep can be much smaller than full-step holding torque.
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?
More supply voltage requires a regulating driver and correct ratings. Do not connect a low-voltage stepper directly to a higher supply merely to gain speed. A suitable current-regulating driver, configured current limit, insulation rating, overvoltage strategy and thermal design are required.
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
- AN-323: Microstepping Drive Circuits for Single Supply SystemsAnalog Devices · 2026-10-13Manufacturer application note reviewed for quadrature phase currents, static position error from load and current errors, and closed-loop considerations.
- AN-026: Programmable Adaptive Microstep TableAnalog Devices · 2026-10-13Manufacturer application note reviewed for motor-dependent microstep behavior, waveform optimization, production tolerance, friction and ripple-torque effects.
- DRV8825 Stepper Motor Controller IC DatasheetTexas Instruments · 2026-10-13Datasheet reviewed for discrete microstep modes, current tables, PWM current regulation, decay modes, voltage range and protection boundaries.
- Stepper Motor BasicsOriental Motor · 2026-10-13Motor-manufacturer guide reviewed for microstepping, open-loop operation, vibration and the distinction between command resolution and position verification.