Calculate a practical M906 starting current, check the 4V and 4mH Duet gates, and see the wiring and thermal tests that decide whether a 2.9V NEMA 17 is ready for your printer.
2.9V
Usually inside Duet voltage screen
60%-85%
Recommended M906 tuning band
4mH
Direct-drive inductance gate
M906 start
1100 mA
M906 rounds down in 100 mA steps.
V = I x R
2.9 V
Duet screen gate is 4V max.
Torque pre-screen
53%
Approx. one-phase microstep holding factor.
Interpretation
The voltage, inductance, current percentage, and board current are inside the normal Duet pre-screen envelope.
Board envelope
Duet 2 WiFi / Ethernet: up to 2.4 A peak motor current, VIN 11-25 V in this checker profile.
Next action
Use M906 around 1100 mA as the first bench value, verify coil pairs before plugging in, and log motor temperature after a representative move cycle.
Boundary
This does not certify the motor for your printer. Load, pulley, acceleration, enclosure temperature, cable pinout, and firmware mapping still decide pass/fail.
For this query, the useful answer is not just yes or no. It is a current setting plus the exact evidence that can invalidate it.
Duet3D warns against motors above a 4V rated-voltage gate. A 2.9V winding passes that first screen, but inductance, current limit, cooling, and load still decide the setup.
Action: Check current x resistance and inductance before editing config.g.
M906 is peak current in milliamps. For a 1.5A motor at 75%, the first value is about 1125 mA before board-specific rounding; the equivalent RMS value is about 796 mA.
Action: Do not begin at the full datasheet current unless testing proves cooling and torque need it.
A motor can be low voltage but still too inductive for direct Duet driving at speed. High inductance reduces current rise and can show up as skipped steps on fast moves.
Action: Treat missing inductance as an RFQ or datasheet gap, not as zero risk.
NEMA 17 does not define lead colors. The Duet driver needs one coil on each phase pair; cross-pair wiring can stall, buzz, or stress the driver.
Action: Use a multimeter continuity test before connecting the motor to the board.
M906 math gives a starting value, not a release value. Board airflow, enclosure temperature, acceleration, pulley radius, and duty cycle can move a safe bench value into a field failure.
Action: Log motor and driver temperatures during a representative cycle before production or long print runs.
Use this table beside the checker result when deciding whether to keep the motor, lower current, or change driver architecture.
| Input | Pass | Caution | Fail / redesign | Refs |
|---|---|---|---|---|
| Rated voltage | <= 4V, or current x resistance <= 4V | Voltage label missing or resistance does not match datasheet | > 4V | S2 |
| Phase inductance | <= 4 mH | 3.5-4 mH on fast axes, or missing datasheet value | > 4 mH for direct Duet drive | S2 |
| M906 current | 60%-85% of rated current | 50%-60% torque risk or 85%-90% heat risk | <50% for loaded axes or >90% without thermal proof | S3 |
| Coil pairing | Two low-ohm pairs, cross pairs open | Color code only, no meter test | Cross-pair continuity or unknown 6/8-wire configuration | S6 |
| Supply and use case | VIN inside the exact board range; 24V is common for printer speed headroom | 12V on fast XY motion, or 48V on a 6HC without confirming revision | VIN outside board limit, driver over-current, or thermal fault under cycle | S2, S8-S12 |
A 2.9V winding is only one screen. Board peak-current limits, VIN range, cooling path, and revision can change the correct decision.
| Board | Drivers | Peak current | VIN range | Decision impact | Refs |
|---|---|---|---|---|---|
| Duet 2 WiFi / Ethernet | 5 x TMC2660 | 2.4A peak | 11-25V | A 1.5A 2.9V motor usually fits current; add fan margin above 2.0A motor current. | S8 |
| Duet 2 Maestro | 5 x TMC2224 | 1.6A peak | 11-25V | Closer to the ceiling for 1.5A motors; avoid starting near rated current without airflow and confirm firmware support for the deployed RRF branch. | S9 |
| Duet 3 Mini 5+ | 5 x TMC2209 | 2.0A peak | 11-25V | Good for many 2.9V NEMA 17 axes, but thermal evidence is still a warning/overtemp signal path. | S10 |
| Duet 3 Mainboard 6HC | 6 x TMC2160 / TMC5160 | 6.3A peak | 11-48V on v1.02; 11-32V on earlier listed revisions | Current headroom is usually not the limiting factor; confirm revision before using 48V. | S11 |
| Duet 3 Toolboard 1LC | 1 x TMC2209-class tool driver | 1.6A peak / 1.1A RMS | 12-32V | Good for lower-current extruder motors; do not assume mainboard current headroom. | S12 |
The commands are useful, but they do not replace coil identification, board-limit checking, or external-driver current setup.
| Command / topic | Use | Limitation | Action | Refs |
|---|---|---|---|---|
| M906 | Sets peak motor current in mA for assigned internal drivers. | External drivers set current on the driver hardware, not through M906. | For a 1.5A motor at 75%, start around 1125 mA peak before board rounding; compare RMS only after dividing by 1.414. | S3 |
| M906 on multi-motor axes | Applies the first axis current parameter to all motors assigned to that axis. | Do not mix unlike motors on one axis and expect individual current tuning from one M906 axis value. | Use identical motors on shared axes, or separate architecture if each side needs independent current. | S3 |
| M569 | Reverses motor direction and sets driver mode/timing parameters. | Direction correction is not a substitute for identifying the two coil pairs first. | Map phases with a meter, then use M569 P# S0/S1 or a deliberate phase swap after power-down. | S4, S6 |
| M308 driver temperature sensors | Can expose driver thermal states on supported boards. | Trinamic drivers report OK/warning/error states; some boards do not provide a normal continuous driver temperature value. | Use firmware flags plus physical airflow and motor temperature checks, not a single dashboard number. | S3, S10 |
The same 2.9V label can lead to different decisions once current, inductance, board family, and cooling change.
Setup: 2.9V, 1.5A, 1.93 ohm, 2.8 mH, Duet 2 WiFi, 24V supply
Result: Start near M906 X1100 Y1100 after rounding. Validate belt tension, acceleration, and motor temperature before increasing current.
Setup: 2.9V, 1.5A, 1.93 ohm, 5.5 mH, fast CoreXY motion
Result: Do not treat 2.9V as enough evidence. Quote a lower-inductance motor or use external drive validation for the speed target.
Setup: 2.9V, 1.0A, direct toolboard drive, constrained airflow
Result: Start lower, confirm active cooling, and watch toolhead heat soak. Board current limit may be lower than the motor datasheet current.
Setup: Listing says 2.9V NEMA 17, but no current, resistance, or inductance
Result: Treat as incomplete. Request a datasheet or measure resistance, then run the checker before wiring it to a Duet board.
The page is specific to Duet, but it should still show the trade-off when current or heat makes a different architecture more practical.
| Option | Best for | Strength | Limit |
|---|---|---|---|
| Direct Duet driver + 2.9V NEMA 17 | Most RepRap-style printer axes when current and inductance fit | Simple wiring, firmware current control, no external driver BOM | Board heat and current ceiling are the main gates |
| External stepper driver | High-current motors, heavy Z axes, CNC-style loads | More current headroom and thermal separation from control board | More wiring, more configuration, more failure points |
| Lower-current low-inductance motor | Toolboards, compact enclosed printers, light axes | Lower heat and easier direct-drive validation | Less torque reserve if acceleration or load is high |
| Higher-voltage or high-inductance legacy motor | Reuse only after data-backed validation | May be physically available in existing machines | Often a poor direct Duet candidate despite the NEMA 17 frame |
These are the mistakes most likely to turn a plausible M906 value into a failed motion system.
Users may think a 2.9V motor needs a 2.9V power supply. Chopper drivers normally use a higher supply and current limiting.
Mitigation: Set current with M906 and keep VIN inside Duet board limits; do not power the printer from the motor rated voltage.
Motor and driver heat can climb, especially in enclosed printers or without airflow.
Mitigation: Start 60%-85% of rated current, then tune from measured skipped-step and temperature data.
The motor may pass a low-speed bench jog but lose torque at speed.
Mitigation: Keep direct Duet candidates at or below the 4 mH gate, especially for XY or extruder use.
Crossed phases can produce buzzing, stalls, wrong direction, or driver stress.
Mitigation: Map coil pairs with a meter; use M569 or a controlled phase swap only after the pairs are known.
A value that is reasonable on a 6HC can exceed the current or supply limits of a Toolboard 1LC, Maestro, Mini 5+, or Duet 2 board revision.
Mitigation: Match the checker board selection to the exact PCB and confirm VIN/current limits from the hardware page before editing config.g.
When a setup moves to an external stepper driver, current may be set by jumpers or driver configuration instead of Duet firmware.
Mitigation: Treat M906 as the internal-driver setting only; document the external driver current method in the validation record.
Evidence last checked 2026-06-10; stage1b refresh 2026-06-10. Review every 6 months, and immediately after Duet firmware, board current limits, motor datasheet, wiring harness, or printer motion targets change.
| ID | Source | Key data | Why it matters | Checked |
|---|---|---|---|---|
| S1 | SERP evidence for "2.9v nema 17 duet" | Public results mix Duet setup questions, motor listings, and generic NEMA 17 pages. The visible intent is ambiguous: users need both a quick current-setting answer and confidence about electrical compatibility. | Supports a hybrid page: the first screen must calculate an M906 starting point, while the report explains limits and evidence. | 2026-06-10 |
| S2 | Duet3D documentation: choosing motors | Duet3D guidance says to avoid motors with rated voltage, or rated current multiplied by phase resistance, above 4V. It also says to avoid motors above 4 mH inductance when driven directly by Duet boards. | A 2.9V label is usually inside the voltage gate, but inductance and actual current x resistance still need checking. | 2026-06-10 |
| S3 | Duet3D documentation: M906 motor currents | Duet3D says M906 sets peak current in milliamps, notes RMS current is peak divided by 1.414, recommends 60%-85% of rated maximum current, and says external drivers set current outside firmware. | The checker defaults to 75%, reports M906 in peak milliamps, and avoids claiming M906 controls external drivers. | 2026-06-10 |
| S4 | Duet3D documentation: M569 motor direction | Duet firmware can reverse motor direction with M569; direction correction does not require swapping random motor leads when coil pairs are already known. | Prevents unsafe trial-and-error wiring when a motor runs backward. | 2026-06-10 |
| S5 | NEMA standards context | NEMA frame naming identifies mechanical frame families. It does not define winding voltage, rated current, lead order, connector pinout, torque, or thermal behavior. | This page has a distinct angle from generic NEMA 17 pages: Duet current setup for a low-voltage winding. | 2026-06-10 |
| S6 | NEMA17Motor wiring checker | Existing continuity workflow maps 1A/1B and 2A/2B from low-ohm coil pairs before energizing a driver. | A correct M906 value is not enough if the four motor leads are cross-paired. | 2026-06-10 |
| S7 | NEMA17Motor current fit checker | Driver-current screening should include rated current, driver limit, thermal headroom, and practical validation rather than a single current number. | Connects the Duet-specific M906 result to a broader motor-current validation path. | 2026-06-10 |
| S8 | Duet3D hardware: Duet 2 WiFi / Ethernet | The Duet 2 WiFi/Ethernet hardware page lists five TMC2660 drivers up to 2.4A peak, 11-25V input power, and says a cooling fan is always required above 2.0A motor current. | A 2.9V NEMA 17 that fits the winding gates can still fail the board thermal/current gate on Duet 2. | 2026-06-10 |
| S9 | Duet3D hardware: Duet 2 Maestro | The Duet 2 Maestro hardware page lists five TMC2224 drivers up to 1.6A peak, 11-25V input power, cooling guidance for higher stepper currents, and notes RRF support limits for later firmware. | Maestro is a lower-current Duet 2 board, so a 2.9V NEMA 17 near 1.5A needs tighter cooling and firmware-version checks than a generic Duet answer suggests. | 2026-06-10 |
| S10 | Duet3D hardware: Duet 3 Mini 5+ | The Duet 3 Mini 5+ hardware page lists five TMC2209 drivers up to 2.0A peak, 11-25V input power, and driver-temperature flags rather than a normal continuous temperature reading. | Tool output should not imply one universal Duet current limit or full thermal telemetry across boards. | 2026-06-10 |
| S11 | Duet3D hardware: Duet 3 Mainboard 6HC | The 6HC page was updated 2026-05-11 and lists six TMC2160/TMC5160 drivers up to 6.3A peak. VIN depends on revision: 11-48V for v1.02, 11-32V for earlier listed revisions. | High-current Duet boards change the current answer, but board revision still controls supply-voltage limits. | 2026-06-10 |
| S12 | Duet3D hardware: Duet 3 Toolboard 1LC | The Toolboard 1LC page lists 1.6A peak / 1.1A RMS stepper capacity, 12-32V input power, and very small combined 5V/3.3V accessory current allowance. | A direct-drive extruder motor may pass voltage and inductance checks but still need a lower current target on a toolboard. | 2026-06-10 |
Grouped answers for setup, electrical limits, wiring, and validation.
Run the checker, verify coil pairs, then collect temperature and skipped-step data under your real movement profile.
