CHIHAI CHS-GM20-20BY Geared Stepper Motor

Overview

The CHIHAI MOTOR CHS-GM20-20BY is a 20 mm geared stepper with a two-phase four-wire motor and metal reduction gears. Choose one of ten ratio options and a motor-only, bracket or reciprocating-driver package. This compact electric motor provides ratio-dependent output steps, speed and torque for positioning mechanisms.

Features

Metal reduction gears in a compact cylindrical housing.
18° input motor step with finer output increments through the gearbox.
4 mm D-shaped output shaft with a 3.5 mm flat reference.
Four-wire PHR-4 connection and accessible PCB wiring.
Optional lightweight anodized mounting bracket and button-operated reciprocating driver.

Specifications

Specification	Value
Brand / model	CHIHAI MOTOR / CHS-GM20-20BY
Motor / transmission	Two-phase four-wire bipolar stepper; metal reduction gears
Supply range / test reference	5–12V DC operating reference; electrical tests at 12V DC with L6219 driver reference
Diameter / motor section	20 mm /18.6 mm drawing reference
Gearbox length L	16,17.5,19 or20.5 mm, depending on ratio; drawing tolerance ±0.3 mm
Motor input step	18° per step
Phase resistance / inductance	20 Ω ±7% /11 mH per phase
Phase current / excitation	600 mA per phase at 12V reference /two-phase excitation
Input pull-out torque	>32 gf·cm at 500 pulses/s
Input holding torque	>60 gf·cm at 0 pulses/s
Input response / starting frequency	>1200 pulses/s response; >900 pulses/s starting
Practical pulse-rate guide	300–1000 pulses/s; start around 300 pulses/s, stable-speed reference around 700 pulses/s
Winding insulation / dielectric test	Class E coils /100V AC for one second
Insulation resistance	100 MΩ, tested at 500V DC
Operating temperature reference	0 to+55°C
Motor weight	Approximately47 g; varies with reduction ratio
Output shaft diameter / D-flat	4 mm, +0/−0.03 mm /3.5 mm, +0/−0.1 mm
Shaft projection / flat length	10.5 ±0.5 mm drawing reference (10 mm nominal in product table) /7 mm
Front mounting	Two ISO M2.5 ×2 tapped holes;15 mm spacing
Other drawing references	7 mm front register diameter;3 mm front offset;1 mm rear offset;6 mm rear shaft/bearing reference
Connector / wire length	PHR-4 /140 ±5 mm
Pin order / coil pairs	Pin1 yellow and pin2 red: phase A; pin3 black and pin4 blue: phase B
Gearbox maximum instantaneous load	6.0 kgf·cm; do not exceed, and do not treat as continuous torque rating

Ratio Selection and Performance

Three selectors use rounded nominal ratio names: 12 corresponds to 12.5:1, 31 to 31.25:1 and 62 to 62.5:1. The remaining selectable nominal labels are 25,50,78,100,125,195 and 250. The selector includes these nominal-to-precise mappings.

The following 12V table uses 700 input pulses/s. Additional ratios 156, 312.5,390 and 488 are series references and are not current selectable configurations. L is the gearbox-length reference. No-load speed, holding torque and pull-out torque are separate operating conditions.

Precise ratio	Selectable nominal / scope	L (mm)	Output step (°)	No-load rpm at 700 pulses/s	Holding torque (kgf·cm)	Pull-out torque (kgf·cm)
12.5:1	12	16	1.44	168	≥0.5	≥0.3
25:1	25	16	0.72	84	≥1.2	≥0.6
31.25:1	31	16	0.576	67	≥1.5	≥0.75
50:1	50	17.5	0.36	42	≥2.5	≥1.2
62.5:1	62	17.5	0.288	33	≥3.0	≥1.5
78:1	78	17.5	0.23	27	≥3.8	≥1.7
100:1	100	19	0.18	21	≥5.0	≥2.50
125:1	125	19	0.144	17	Maximum 6.0	≥3.5
156:1	Series reference only	19	0.115	13	Maximum 6.0	≥4.5
195:1	195	19	0.092	10	Maximum 6.0	≥6.0
250:1	250	20.5	0.072	8	Maximum 6.0	Maximum 6.0
312.5:1	Series reference only	20.5	0.0576	6	Maximum 6.0	Maximum 6.0
390:1	Series reference only	20.5	0.0462	5	Maximum 6.0	Maximum 6.0
488:1	Series reference only	20.5	0.037	4	Maximum 6.0	Maximum 6.0

The cells marked Maximum give permissible limits, not guaranteed minimum torque. The gearbox's maximum instantaneous load is 6.0 kgf·cm; exceeding it can damage the gearbox and motor. It does not establish a continuous-duty rating.

Output speed in rpm = output step angle in degrees ×input pulse rate per second ×60 ÷360. There are 60 seconds per minute and 360 degrees per revolution. Speed depends on pulse rate and load; begin at a suitable starting frequency rather than assuming the highest no-load speed is available under load.

Wiring and Control

Use a compatible two-phase bipolar stepper driver. Connector pin order is 1 yellow,2 red,3 black,4 blue. Yellow/red form phase A and black/blue form phase B. Identify each coil pair and confirm direction with the actual driver before integrating the mechanism. The drawing shows the excitation sequence viewed from the flange side.

The motor requires a sequenced stepper drive rather than a direct two-wire DC connection. The recommended 300-pulse/s starting point and roughly 700-pulse/s stable-speed reference are application guides; the separate input-motor frequency specifications are test references. Actual starting and load capability depend on the driver, ratio, supply and mechanism.

The reciprocating-driver packages include the displayed button-operated board. Check its actual power and control terminal markings before connection; the motor's supply range does not establish all controller input limits or external signal compatibility.

Mechanical Installation

Select the ratio before designing the mounting envelope: gearbox length changes from 16 to 20.5 mm across the reference family. Check the shaft projection, D-flat, tapped mounting holes and wire clearance against the mechanism. Avoid forcing the shaft, stalling or applying an impact load.

Optional mounting bracket	Specification / scope
Construction / mass	Anodized aluminum alloy;3 mm thick; approximately 6.5 g
Overall drawing references	31 mm high ×23 mm base depth;16 mm front flat width
Motor face hole pattern	17 mm horizontal and 15 mm vertical references;18.5 mm lower offset;7.1 mm center aperture;two 3.1 mm hole references
Base attachment	Two M5 threaded holes;23 ×16 mm base reference
Base hole offsets	5 mm from first edge,10 mm hole spacing,8 mm to opposite edge;8 mm transverse offset
Mounting example scope	The illustrated CHR-GM20/25-style DC motor is a bracket-fit example; it is not a second included motor

Applications

For compatible small positioning mechanisms, hobby robotics, model equipment and automation assemblies when the required resolution, torque, pulse drive and mechanical dimensions match the selected configuration.

What's Included

Selected package	Contents
Motor Only	1 × selected geared stepper motor
Motor + Mounting Bracket	1 × motor and 1 × blue mounting bracket
Motor + Reciprocating Driver	1 × motor and 1 × button-operated reciprocating driver
Motor + Bracket + Reciprocating Driver	1 × motor,1 × bracket and 1 × reciprocating driver

Each configuration includes one motor at the chosen ratio. A bracket and driver are included only when named in the package. A power supply, host controller and the DC motor shown in the bracket mounting example are not included.