Planetary Gear Reducer Basics

Planetary gear reducers are a specific type of in-line gearing that provide unmatched torque versus size, precision, and durability compared to other in-line gear technologies. The purpose of a planetary gear reducer is to multiply the torque of an electric motor while proportionally reducing the speed with maximum efficiency. Planetary gear reducer design consists of an input sun gear that turns several orbiting planet gears within an outer ring gear (image, below).

Either directly machined or coupled to the motor shaft, the sun gear rotates as the motor generates torque. As the sun gear rotates, it drives planetary gears around the fixed outer ring gear, like planets orbiting the sun. Torque is transmitted through the planet gears to the reducer output shaft through the planet carrier. The relative diameters (tooth counts) of the sun, planet, and ring gears ultimately determine the gear ratio and load capacity of the gear reducer.

High precision motion control applications, such as medical hand tools, patient lifts, and automatic door openers, benefit from planetary gearheads that offer high torsional stiffness and low backlash.

Two different types of gears can be used within planetary gear reducers, spur or helical. Helical gears offer a higher tooth contact ratio that improves the torque capacity and life of the gear reducer while decreasing backlash. Spur gears provide slightly less tooth contact area resulting in less torque capacity and torsional rigidity, but still provide excellent efficiency and durability with a slight cost advantage.  Planetary gear reducers can also incorporate multiple gear stages to provide higher gear ratios.

Frequently applied in high-performance automated equipment applications, planetary gear reducers with integrated electric motors offer:

• Tremendous torque versus speed performance capabilities
• High-precision with low-backlash
• Extremely high efficiency
• Excellent durability in a compact, in-line form factor
• Ability to handle dynamic, high-duty cycle applications
• Applicable with any motor technology, including brushless, brushed, stepper or servo motors.

Planetary gearheads are customizable and available with a variety of design features to meet specific environmental and unique requirements, resulting in optimal solutions for nearly any commercial or industrial equipment application.

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