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Tech Tip: Planetary Gearboxes

Video Transcript

Hello!  This is Paul with a Groschopp Tech Tip.  Today we will be discussing planetary reducers – how they work, advantages, and disadvantages.

We’ll begin with the planetary’s layout.  Simple planetary gears are arranged with a centrally-located, externally-toothed sun gear that meshes with one or more externally-toothed planet gears.  As the name implies, the “planet gears” rotate around the “sun gear.”  The planet gears also mesh with an internally-toothed ring gear—which encompasses the entire gear set.

The construction of the planetary reducer lends itself to many advantages, for example:

  • Planetary reducers give you high torque in a compact package; sharing the load between several planet gears allows the reducer to handle the same torque that larger parallel axis gear sets handle.  
  • They are highly efficient with a single stage typically 95% efficient.
  • These reducers provide for ratios as high as 11:1 to be achieved in a single stage, whereas, it is difficult to achieve much higher than 5:1 in a single parallel axis stage.
  • Since the sun gear contacts multiple planet gears, resistance to elastic deformation, is higher in a planetary gear set than parallel axis gear set, giving the planetary reducer high torsional stiffness.
  • They allow for coaxial alignment, meaning no offset output shaft in relation to the motor shaft.
  • The output shaft on Planetary reducers rotates in the same direction as the motor without needing an idler gear, as in a parallel axis gear set.  
  • Planetary reducers are ideal for intermittent duty applications but also can be used in continuous duty applications.
  • Finally, Groschopp planetary’s have an integrated housing, meaning the ring gear is integrated into the outer housing for the gearbox, adding to the robusticity.
  • Compared to the advantages of the planetary reducers, the disadvantages are minimal for most applications for example:
  • High ratio of length to diameter when using multiple stages (gearhead can get very long).
  • Potentially high cost if low backlash, high precision gearing is required.
  • Specific numbers of gear teeth are required equally spaced planets (ease of assembly) and noise mitigation.
  • The gear ratio determines how many planet gears may be used.

You should consider planetary reducers when designing for applications requiring high torques in a small package with an output shaft needs to be co-axially aligned with the motor.

This has been a Groschopp Tech Tip.  For more information about any of our products or to view other Tech Tips please visit us online at www.groschopp.com

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