Miniature gear motors consist of a motor and a reduction gearbox. The motor serves as the power source, operating at high speed with relatively low torque. The rotational motion of the motor is transmitted to the reduction gearbox through the motor gear (including worm gears) mounted on the motor shaft. Therefore, the motor shaft is one of the most critical components in miniature gear motors.
The choice of shaft material must take into account torque requirements, machinability, corrosion resistance, and in some cases, magnetic properties depending on motor design. Common shaft materials include high-quality carbon steel, stainless steel, alloy steel, and carburized steel. The most widely used materials are:
SAE 1141 & 1144 Steel (Equivalent to Chinese 45# Steel):
Most commonly used in the industry due to its low cost and easy availability.
Easy to machine.
Main drawback: prone to rust, requiring anti-rust oil coating during use.
SAE 416 Stainless Steel (Equivalent to Y1Cr13):
Less machinable, not ideal for complex features (e.g., threaded shaft heads).
More expensive than 45# steel, cheaper than 303 stainless steel.
Widely used due to its corrosion resistance.
SAE 420 Stainless Steel (Equivalent to 2Cr13):
Similar machining limitations as 416.
Priced between 45# steel and 416/303 stainless steels.
Offers good corrosion resistance and is widely applied.
SAE 431 Stainless Steel:
Less commonly used.
Higher chromium content, suitable for food-contact applications.
SAE 303 Stainless Steel:
Higher cost.
Softer material, excellent machinability, suitable for complex shaft geometries.
As the motor gear and the first-stage gear in the gearbox mesh, torque is generated. The fit between the motor gear and motor shaft directly impacts transmission performance. Common shaft types include:
Smooth Shaft: Suitable for light loads and low torque.
Flat Shaft / D-type Shaft: Designed for medium loads.
Knurled Shaft: Also suitable for medium loads.
Keyed Shaft: Used in heavy-load, high-torque applications.
Worm Shaft: A special type used for worm-and-gear transmission systems.
| Smooth Shaft | Flat Shaft / D-type Shaft | Knurled Shaft | Keyed Shaft |
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The manufacturing quality of motor shafts directly affects the lifespan of miniature gear motors. Key requirements include:
Dimensional Precision: Shaft diameters can be controlled within ±0.002 mm.
Surface Treatment: Nickel plating is often applied for corrosion protection.
Surface Roughness: Critical to ensure proper gear-shaft fit and smooth operation.
Gearboxes are classified by power (high-power or low-power), and the transmission shafts differ accordingly. Shafts are typically divided into input shafts and output shafts.
Output Shaft:
Connects the gearbox to the driven mechanism.
Operates at much lower speed than the input shaft.
Can be customized in different shapes: D-shaft, round, double-flat, hexagonal, pentagonal, square, etc.
Made of metal or engineering plastics depending on application.
Input Shaft:
Connects the motor to the gearbox.
Transmits high speed with low torque.
One end fits into the housing to mesh with gears; the other end is slotted for the motor shaft.
Uses a key-slot design to achieve stable and quick assembly.
Function & Differences:
Both shafts transmit power.
Input shaft: high speed, small torque, smaller diameter.
Output shaft: low speed, high torque, larger diameter.
Under normal operation, motor bearings should not overheat. Excessive heating may result from:
Bearing damage.
Contaminated lubricant (foreign particles).
Insufficient lubrication.
Poor lubricant quality or inappropriate viscosity.
Improper assembly (bearings too loose or too tight).
Misalignment during installation.
Axial play (shaft end movement) in miniature motors may arise from:
Improper fit between rotor core and shaft.
Missing or damaged thrust washers.
Magnetic center misalignment between stator and rotor.
Axial forces generated by fans or propellers attached to the shaft.
Consequences include abnormal vibration, noise, bearing failure, winding burnout, and shortened motor lifespan. Axial play can be mitigated using wave spring washers between bearings and end caps.
Planetary gear motors are widely used in smart home devices and other applications. Bearing selection considerations include:
Common Types: Self-aligning roller bearings, tapered roller bearings (single/double row), cylindrical roller bearings, four-point contact bearings, ball bearings.
Input Shaft Bearings: Require high load capacity due to high speed.
Intermediate Shaft Bearings: Must handle combined forces from multiple gear meshes.
Output Shaft Bearings: Low speed, larger torque; requires higher load capacity if subject to impact.
Gearbox shaft fracture typically results from:
Improper Motor-Gearbox Selection:
Rated torque of the motor × reduction ratio must remain below the rated torque of the gearbox model.
Failure to account for overload torque may cause shaft breakage.
Excessive Load Torque:
Operating torque exceeding gearbox design limits increases stress on the output shaft, leading to fracture.
For applications such as baby rockers, rocking cradles, smart soap dispensers, micro pumps, peristaltic pumps, diaphragm pumps, garbage disposers, massage equipment, e-bikes, and shaving devices,
In gearbox applications, conventional POM and nylon gears often face issues such as:
High noise levels.
Insufficient wear and fatigue resistance.
Brittleness (POM) or torque limitations (PA12, TPEE).
Dimensional instability due to moisture (PA46).
Lihua Motor’s engineering solutions integrate advanced gear materials featuring:
Excellent wear resistance.
Low-noise performance.
High toughness.
Corrosion resistance.
Dimensional stability (unaffected by humidity).
These material advantages significantly enhance the reliability, noise reduction, and lifespan of miniature gear motors across multiple industries.
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