The 57 mm frame (NEMA 23) is the most-used stepper size in automation, and its 3-phase version trades a little holding torque for a 50% finer step angle — 1.2° versus the 1.8° of 2-phase motors — delivering smoother motion, lower vibration and better low-speed accuracy. This guide collects the parameters engineers actually cross-reference when sizing a 3-phase 57 mm motor: torque by stack length, current, speed behavior and closed-loop options, with real datasheet numbers.

Why choose 3-phase in a 57 mm frame

A 3-phase hybrid stepper energizes three windings 120° apart instead of two 90° apart. The torque ripple per electrical cycle is therefore lower — the measured benefit is 30–40% less vibration at low speed and audibly quieter operation, which matters for medical devices, optics stages and inspection machines. The 1.2° full step gives 300 steps/rev instead of 200, so even before microstepping, resolution is 1.5× finer. The trade-offs: 3-phase drivers are slightly more complex, and for the same frame the peak holding torque runs somewhat below an equivalent 2-phase motor — which is why selection should be by torque requirement, not by phase fashion.

Core parameter table (57 mm / NEMA 23 3-phase)

The table below uses measured data from a current 3TC57 closed-loop series (matched driver, 48 V DC), representative of what a modern 57 mm 3-phase motor delivers:

Model	Step angle	Holding torque	Phase current	Body length	Low-speed torque
3TC57-10 (closed loop)	1.2°	1.0 N·m	5.8 A	40 mm	≈1.0 N·m @<300 rpm
3TC57-20 (closed loop)	1.2°	1.9 N·m	5.8 A	48 mm	≈1.8 N·m @<300 rpm
3TC57-30 (closed loop)	1.2°	3.0 N·m	5.8 A	56 mm	≈2.9 N·m @<300 rpm

General specification of the series: step accuracy ±5% (full step, no load), insulation class B, ambient range −20 °C to +50 °C, radial play 0.02 mm, maximum radial force 75 N at 20 mm from the flange. Open-loop 3-phase equivalents (3TO57 family) share the same 1.2° step angle and frame dimensions for drop-in mechanical interchangeability.

How speed changes the torque you actually get

The holding-torque column is a standstill number. On a 48 V supply with a matched driver, the measured pull-out curve of the 3TC57-20 holds roughly 1.8 N·m up to 300 rpm, still delivers about 1.0 N·m at 1200 rpm, and remains usable to approximately 1800–2000 rpm where torque falls toward a few tenths of a N·m. Practical sizing rule: read torque at your working speed with 30–50% margin, and remember that raising supply voltage from 24 V to 48 V visibly lifts the whole high-speed half of the curve — on the same motor and driver.

Open loop or closed loop

Open-loop 3-phase motors (3TO series) accept pulse/direction or bus commands and suit predictable loads — their 1.2° step already smooths motion without an encoder. Closed-loop 3-phase motors (3TC series) add an encoder and close the position loop in the drive: stall detection, position alarm, automatic correction after disturbance, and cooler running at partial load. For 57 mm applications with varying friction — dispensing, capping, sliding gates — the closed-loop premium typically repays itself through avoided scrap and downtime.

FAQ

Q: Is a 3-phase motor compatible with a 2-phase driver?
A: No. Winding layout and drive commutation differ. Match 3TO motors with 3-phase drivers and 3TC motors with their matched closed-loop drivers — both are listed on each motor’s product page.

Q: Why does my 2-phase 57 motor show more holding torque than the 3-phase?
A: Per equal frame and stack, 2-phase peaks higher holding torque; 3-phase wins on smoothness, noise and low-speed accuracy. Choose by what the mechanism actually needs — positioning quality or raw stall torque.

Q: What driver current should I set for 5.8 A motors?
A: Set the driver to the motor’s rated phase current (5.8 A peak for this series) or slightly below for cooler running; never above, since torque gain is minimal and heating is not.

Summary

Size by torque-at-speed with margin, choose 3-phase for smoothness-critical axes, and prefer closed loop where loads vary. Browse 3-phase open-loop stepper motors and 3-phase closed-loop stepper motors for the full 57/86/110 frame range, including the 3TC57 series whose data appears above.