Four wires describe a connection
A standard four-lead bipolar motor exposes the two ends of each phase coil. Wire count does not tell you the motor’s step angle, rated phase current, or torque; confirm those values for the exact model.
2-Phase 4-Wire Micro Stepper MotorResolution Calculator
Estimate command pulses per revolution or millimeter, then check wiring, current limits, and positioning caveats.
Use the calculatorWhat the calculator tells you
Use the result to configure a controller’s pulse scaling. Use the motor datasheet and a test of the assembled mechanism to decide whether it will meet the application’s load and positioning needs.
The calculator estimates command spacing
It converts full-step angle, driver microstep mode, and travel per revolution into controller pulses. Friction, backlash, load, motor tolerances, and driver current control determine how closely motion follows those commands.
Use model-specific current limits
Micro motors do not share one safe current or resistance range. Set the driver from the motor and driver documentation, then check temperature under the real duty cycle.
Example: one documented 15 mm motor
MOONS’ 15PM020S0-01002 is the source for the calculator’s 18° example angle. Its published specifications illustrate one model; they should not be generalized to every micro stepper.
| Published parameter | MOONS’ 15PM020S0-01002 | How to use it |
|---|---|---|
| Configuration | 2 phases; bipolar coil type | Confirms this example is a two-phase bipolar model. |
| Full-step angle | 18° (20 full steps/revolution) | Sets full steps per revolution: 360° ÷ 18° = 20. |
| Nominal voltage | 5 V DC | Follow the motor and driver current-control instructions before choosing a supply. |
| Phase resistance | 10.5 Ω ±10% at 20°C | Use the specified test temperature and tolerance; do not apply another motor’s resistance range. |
| Holding torque | 3.6 mN·m | A holding value is not a torque-versus-speed curve or a load guarantee. |
Source checked 2026-10-06. Product data can change; confirm the current datasheet for the exact model before purchase or wiring.
For a separate mounting and model-fit comparison, see the 15 mm 4-wire motor fit guide.
Read the motor label before choosing a driver
Wire count helps identify connection topology. It cannot replace the model-specific values that determine motion and electrical compatibility.
| Label or value | What it tells you | What to verify |
|---|---|---|
| Four-lead connection | A standard two-phase bipolar motor exposes two ends for each phase coil. | The exact pinout and wire colors in the motor documentation. |
| Full-step angle | The motor’s full-step command count per revolution: 360° divided by the angle. | The exact part’s datasheet; wire count does not specify step angle. |
| Current and torque | Nothing quantitative from wire count alone; these depend on motor design and operating point. | Rated phase current, torque curves, thermal limits, and driver capability. |
Microstepping changes pulse count, not guaranteed accuracy
For the 18° example above, assume 1.0 mm of travel per motor revolution. The listed increment is the theoretical command distance per pulse, not a measured movement specification.
| Driver mode | Command pulses / rev | Theoretical distance / pulse |
|---|---|---|
| Full step (1×) | 20 | 50 µm |
| 1/4 step | 80 | 12.5 µm |
| 1/16 step | 320 | 3.125 µm |
| 1/32 step | 640 | 1.563 µm |
Positioning limit
TI’s analysis gives about 9.8% of full-step holding torque as the theoretical incremental torque at 1/16 microstepping. If that increment cannot overcome the actual load, friction, and detent torque, several commands may be needed before the shaft moves. Use measured travel and the motor manufacturer’s guidance when accuracy matters. See the TI application report for the assumptions and analysis.
Identify and connect the two coil pairs
Wire colors are not a reliable substitute for a motor pinout. Use the datasheet when available; otherwise identify the pairs with resistance measurements before connecting a driver. SparkFun's coil-pair identification guide covers this check. Basic pair-to-output wiring is shown in the Pololu four-lead bipolar guide. For a dedicated phase-pair check, use the two-phase four-wire wiring tool.
- 1
Power down and disconnect
Turn off the motor supply and disconnect the motor from the driver before using a multimeter in resistance mode.
- 2
Measure all lead combinations
The two ends of one winding show a finite resistance. Leads from different windings remain open. Record the two pairs; the exact resistance depends on the motor.
- 3
Connect one pair to each phase
Connect one coil pair to A1/A2 and the other to B1/B2, or use the equivalent labels in the driver manual. Do not cross wires from different coils.
- 4
Set current, then test slowly
Set phase current from the motor rating and driver instructions before enabling power. If direction is backward, power down and swap the two wires of one phase.
Pairing diagram only. Confirm terminal names in the driver manual.
Selection limits and risk controls
Check these items against the exact motor, driver board, and mechanism before a powered test.
Current set above the motor rating
Risk: Excess winding current can overheat a small motor or reduce its service life.
Check: Start from the motor’s rated phase current and the driver’s current-setting procedure. Check motor and driver temperature after reaching steady operation.
Microstep setting treated as measured accuracy
Risk: Commanded increments can be smaller than the motion the motor can produce under load.
Check: Use the calculator for controller pulse scaling. Measure the assembled mechanism under its working load when position accuracy matters.
Motor leads moved while powered
Risk: Changing motor connections with a driver energized can damage the driver or interrupt motion unexpectedly.
Check: Disable motor power before changing any phase connection. Verify the coil pairs and current limit before the first powered test.
Do not connect or disconnect motor leads while a driver is powered; see the SparkFun driver warning.
Evidence and calculation method
The calculator uses published motor angle and configured driver division; it does not estimate torque, electrical current, or measured axis accuracy.
1. Full steps per revolution
360° ÷ motor full-step angle
2. Command pulses per revolution
full steps × driver microsteps per full step
3. Linear pulse scaling
pulses per revolution ÷ travel per revolution
MOONS’ 15PM020S0-01002 product specification
Manufacturer listing for one 15 mm, two-phase bipolar sample: 18° step angle, 5 V nominal voltage, 10.5 Ω ±10% resistance at 20°C, and 3.6 mN·m holding torque. This is a model example, not a universal micro-motor range.
MOONS’ Industries · Checked 2026-10-06
How to Improve Motion Smoothness and Accuracy of Stepper Motors
TI explains that incremental torque decreases as microsteps divide a full step; actual movement depends on whether incremental torque exceeds load, bearing friction, and detent torque.
Texas Instruments, application report SLOA293A · Checked 2026-10-06
Four-lead bipolar stepper motor connections
Shows one coil pair connected to each bipolar driver output pair and explains that swapping one coil pair reverses direction, while mixing leads from different coils causes erratic motion.
Pololu, Application Note 0J88 · Checked 2026-10-06
Choosing a stepper motor and controller
Explains how motor rated current, driver current capability, supply voltage, and current limiting constrain a compatible setup.
Pololu Tic User’s Guide · Checked 2026-10-06
ProDriver and Mini Stepper Motor Driver hookup guide
Documents multimeter-based coil-pair identification for four-wire motors and warns against connecting or disconnecting motor leads while the driver is powered.
SparkFun Learn · Checked 2026-10-06
Frequently asked questions
Have the motor part number, rated current, load, and travel requirement ready for a useful selection review.
Recalculate your pulse scalingPublished 2026-09-26 · Updated 2026-10-06