Advantages and Disadvantages of Planetary Gearmotors

Friday - 17/02/2017 13:44

Advantages and Disadvantages of Planetary Gearmotors

We design all our standard parallel shaft (helical or helical/spur) and right angle (worm or helical/worm) gearboxes in-house, and all gearheads are manufactured and assembled in our main factory.
Occasionally, we’ll receive a request to mate one of our standard AC, DC or BLDC motors to a planetary gearhead. To identify the best gearmotor option for our customer’s application, we review all critical performance requirements and parameters and then propose the most competitive solution.

If gearmotor cost, gearhead noise, and overall gearmotor length are critical factors, we find that design engineers often drop the requirement for a planetary gearhead and instead select a more compact right-angle or inline (helical) gearhead solution.
However, there are certain applications where the benefits of a planetary gearhead outweigh its disadvantages. Below is a brief review of advantages and disadvantages of small planetary gearheads used with fractional horsepower small motors (FHP = <746 Watts) .
Advantages of planetary gearheads:
Compact size and low weight – as much as 50% reduction with same torque output.
High power density – several planets share the load rather than one gear, the more planets the more sharing.
Longer gear life at similar loads.
Gearing can be very accurate with virtually no backlash.
High efficiency – 95% per stage is common.
Typical ratio per stage is 9:1, 4 stages 9000:1
Dolin three phase motor
Coaxial arrangement – no offset output shaft
Modular, most planetary stages can be stacked.
Disadvantages of planetary gearheads:
Noisier Operation – some planetary gearheads are noisy.
Gearing must be accurate to assure load sharing
High bearing loads can lead to early wear in dead stud or sleeve bearing construction
Generally grease lubricated (oil bath is the better).
High ratio of length to diameter when using multiple stages (gearhead gets very long).
High cost if low backlash and long life are required.
Custom Gearmotor:
Type 24VDC or 130VDC brushless DC motor, and type ABL brushless DC motor speed control. This example shows a 2-stage, 14:1, 31 lb-in, 2-inch (52mm) diameter gearhead.
dc motor

The gearhead has a gear strength limit of around 106 lb-in, with available gear ratios from 14:1 – 58:1. Gearing efficiency varies with the number of gear stages. Higher gear ratios require a 3-stage gearhead (available in ratios of up to 393:1, with gear strength limit of up to 221 lb-in). Dolin typically offers gearmotors with either brushless DC (24V and 130V), permanent magnet DC (12/24V and 90/130V), or AC fixed-speed (115VAC, single phase) and AC variable-speed (230VAC inverter duty) motor options.

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