Select a stepper motor using its available torque at the required speed with the intended driver and supply. Holding torque describes energized standstill performance; it is not the running torque available throughout a move. Include acceleration, load inertia and settling requirements in the selection.
What a step command means
A stepper drive changes winding excitation to move the rotor through commanded positions. The basic step angle, drive subdivision and any gearbox determine nominal command resolution. In open-loop operation, commands do not prove that the load reached its target. Overload, resonance or an unsuitable acceleration profile can cause lost position.
Resolution is not the same as accuracy
Microstepping divides the commanded step and can smooth motion. It does not make mechanical error, backlash or load deflection disappear. A gear ratio also reduces nominal output step size, while adding its own errors. Verify repeatability and absolute accuracy at the output under the real load.
Read the speed–torque curve
| Data | How to use it |
| Holding torque | Check the specified energized standstill condition |
| Running torque curve | Compare with load plus acceleration torque at each speed |
| Driver and supply | Use the conditions associated with the curve |
| Current setting | Check torque and temperature at the intended drive current |
| Inertia and acceleration | Check reliable start, stop and speed transitions |
Stepper or servo?
A stepper can suit predictable loads, short positioning moves and straightforward control. A servo system uses feedback to regulate motion and can be appropriate for changing loads or demanding dynamic response. Closed-loop stepper systems also exist. Compare the complete motor, drive, feedback and mechanics rather than treating the names as fixed performance classes.
Holding a load
Energized holding creates heat. Reducing idle current changes available holding torque. If loss of power could allow unacceptable movement, specify an appropriate holding mechanism and validate it at system level. Motor detent torque or a nominal holding-torque figure is not a general substitute for that requirement.
Data to send for selection
- Move distance, time, maximum speed and acceleration profile.
- Load torque, reflected inertia and any gearbox or screw geometry.
- Required accuracy, repeatability and settling time at the load.
- Driver voltage/current limits, temperature and operating cycle.
Technical reference
Oriental Motor: stepper motor basics and torque characteristics