CHIHAI GM25-25BY Geared Stepper Motor

Overview

The CHIHAI MOTOR CHS-GM25-25BY is a 25 mm geared stepper motor with two-phase, four-wire bipolar operation, a metal reduction gearbox and a 4 mm D-shaped shaft. Choose the reduction ratio and a motor-only or driver, mounting-bracket and power-supply package for compact positioning mechanisms.

Features

Permanent-magnet stepper design with reversible rotation and discrete position control.
Metal reduction gears and a protected wiring PCB.
Ten selectable nominal reduction ratios from 4:1 to 100:1.
Optional push-button driver board, enclosed driver, bracket and power supply as named in the package.

Specifications

Item	Specification
Model	CHS-GM25-25BY / GM25GA-25BY
Motor	Permanent-magnet, bipolar, 2-phase 4-wire stepper with metal reduction gears
Rated motor reference	12V DC with L6219 driver; 300 mA per phase
Phase resistance	10 ohm ±7%
Phase inductance	7.5 mH per phase
Input step angle	15 degrees per step
Excitation	2-phase excitation; bipolar drive
Connector	PHR-4, 2.0 mm pitch, white 4-pin
Lead wire	UL1571 AWG28; 150 ±10 mm
Motor diameter	25 mm
Output shaft	4 mm D-shaft; flat dimension 3.5 mm; projection 12 mm; D-flat length 8 mm
Front boss	7 mm diameter
Motor rear length	14.8 mm; gearbox L depends on ratio
Mounting	2 x M3 tapped holes, 17.0 mm spacing; check drawing
Net motor mass	Approximately 75 g; ratio dependent
Pull-out torque, input motor	More than 60 gf·cm at 100 pulses/s
Holding torque, input motor	More than 75 gf·cm at 0 pulses/s
Maximum response frequency	More than 1300 pulses/s
Maximum starting frequency	More than 800 pulses/s in parameter table; application guidance recommends starting at 300 pulses/s
Coil insulation	Class E
Insulation resistance	100 MΩ at 500V DC
Dielectric test reference	100V AC for one second
Operating temperature	-10 to +55 °C

Reduction Ratio and Performance

The selector uses nominal ratios. The 4, 9, 15, 20, 34, 45, 57, 75 and 100 selections correspond to approximately 4.4, 9.3, 15.46, 20.41, 34.01, 44.9, 57, 74.83 and 98.78 reference ratios. The 25.8:1 option is sold but has no separate performance or gearbox-length column. Do not infer its torque or length from adjacent ratios.

The following is a 12V family reference at 700 input pulses/s, not a guarantee for every selected package. Ratios above 100:1 are reference-only and are not sold here. Holding and pull-out torque are different; torque is not a payload rating.

Reference ratio	Output step (°)	No-load rpm at 700 pps	Holding (kgf·cm)	Pull-out (kgf·cm)
4.4	3.4	397.7	≥0.3	≥0.25
9.3	1.61	188.2	≥0.6	≥0.50
15	1.0	116.7	≥1.0	≥0.8
20	0.75	87.5	≥1.3	≥1.0
34	0.44	51.5	≥2.0	≥1.8
44.9	0.33	38.98	≥3.0	≥2.50
57	0.26	30.7	≥3.5	≥3.0
74.8	0.2	23.4	≥5.0	≥4.0
98.8	0.15	17.7	≥6.5	≥5.5
125	0.12	14	≥8.0	≥7.0
165	0.09	10.6	Do not exceed 9.0	Do not exceed 9.0
217	0.069	8.1	Do not exceed 9.0	Do not exceed 9.0
362	0.041	4.8	Do not exceed 9.0	Do not exceed 9.0
478	0.031	3.7	Do not exceed 9.0	Do not exceed 9.0

Mechanical Dimensions

All dimensions are millimetres. The original drawing specifies L ±0.3, a 2.5 mm front section, a 0.5 mm rear step, 6 mm rear boss, 3.7 mm connector offset and 9.2 mm connector height. Use the selected ratio and physical mounting drawing before machining; the 57:1 and 25.8:1 gearbox lengths are not separately specified.

Actual ratio references	Gearbox length L (mm)	Gear stages
4.4 / 9.3 / 15.46 / 20.41	19	2 / 3 / 4 / 4
34.01 / 44.9	21	5
74.83 / 98.78	23	6
164.63 / 217.31	25	7
362.18 / 478.08	27	8

Wiring and Control

Pin 1 yellow is phase B, pin 2 red is the opposite B winding end, pin 3 black is phase A, and pin 4 blue is the opposite A winding end. Coil pairs are yellow/red and black/blue. Use a bipolar stepper driver, not a direct DC connection. Rotation follows the phase excitation sequence; the drawing views rotation from the flange side.

The motor reference is 12V. A 5–24V driver-supply range is discussed for current-controlled operation; higher supply voltage requires appropriate current limiting and does not make every included board or power supply a 24V item. Set phase current appropriately. Guidance suggests starting near 300 pulses/s and increasing toward approximately 700 pulses/s; usable speed depends on load and acceleration. The general 100–1300 pulses/s control range and higher unloaded response references are not guaranteed starting frequencies.

Package Selection

Package	Contents
Motor Only	One motor
Motor + Bracket	One motor + mounting bracket
Motor + Driver	One motor + push-button driver board
Motor + Enclosed Driver	One motor + driver in enclosure
Motor + Bracket + Driver	One motor + mounting bracket + push-button driver board
Motor + Power Supply + Driver	One motor + power supply + push-button driver board
Motor + Bracket + Power Supply + Driver	One motor + mounting bracket + power supply + push-button driver board

The enclosed-driver option includes its case; other driver packages show an open board. Photographed adapter plug style and board revision are visual references; no unverified input rating or control-interface protocol is promised. Motor-only and bracket packages require a separate suitable driver and supply.

Applications

Use the motor for compact indexing, positioning, instrument adjustment and small robot mechanisms where discrete step control and reduction gearing are useful. Match required speed, torque, duty cycle and backlash tolerance to the actual mechanism.

What's Included

One selected motor configuration with its attached four-wire lead. The bracket, driver, enclosure and power supply are included only when named in the chosen package. No complete robot, external controller or other application assembly is included.

Installation and Operation

Keep within the rated load, including shaft loads. Check the coil pairs and current setting before power-up. Increase load gradually during commissioning. Avoid severe impacts and do not force or pry the gearbox shaft. Long operation, supply voltage, speed and load affect motor temperature; provide adequate cooling.

FAQ

Can this four-wire motor connect directly to DC power?

No. It needs the correct two-phase bipolar excitation from a suitable stepper driver.

Is the 25.8:1 option the same as 34:1?

No. It is a separate selectable ratio. Its own torque and gearbox length are not listed, so confirm the required mechanical envelope before installation.