Cycloidal gear profile

[maximumcoolbeans]

I'm designing a bi-cycloidal drive like the one shown here:

(mesmerizing eh?) Bi-cycloidal drives like this include both a male cycloidal gear and a female cycloidal gear. The male cycloidal gear can be considered the sun gear, where the pins are radially outside of the cycloidal gear, and the female cycloidal gear can be considered a ring gear, where the pins are radially inside of the cycloidal gear (the pins are integrated into the eccentric gear in the bi-cycloidal drive above). The tooth profile equations for male cycloidal gears are provided at these two sources (https://stepbystep-robotics.com/hp/robots/cycloidal-drive/ and https://uwaterloo.atlassian.net/wik...427/Cycloidal+Drive+-+Rev+1+Prototype+Journal). Do any of you know where I can find the tooth profile equations for a female cycloidal gear? Any help is appreciated, thanks.

 

[mfgenggear]

Here are some books that may be relevant to cycloidal gear profiles:

• Handbook of Practical Gear Design
  A detailed guide to gear technology that covers the design of all types of gears, from small mechanisms to large industrial applications.
  
  
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• Asymmetric Gearing
  A book by Dr. Alex Kapelevich that summarizes his knowledge on asymmetric gear drives.
  
  
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• Elements of Mechanism
  A book by V. L. Doughtie, P. Schwamb, A. L. Merrill, and W. H. James that includes information on cycloidal gears.
  
  
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• Analytical Mechanics of Gears
  A book by E. Buckingham that includes information on cycloidal gears.
  
  
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Cycloidal gears are often preferred in horology because they can be designed to have only one or two points of contact, which reduces friction. They are also stronger than involute gears for the same pitch, and they are less likely to wear out.

 

[mfgenggear]

OP
The issue with cycloidal gears is all the gear shops are tooled for involute gears. How are you planning to manufacture them. Prototype or production.

 

[maximumcoolbeans]

@mfgenggear Thanks for the recommendations. I downloaded the "Handbook of Practical Gear Design" and went through all the control+F results for "cycloid" and didn't find what I was after. Let me know if you have other suggestions.

About manufaturing, CNC milling seems like an option for prototyping and manufacturing. There are no sharp corners at the root of the teeth, unlike conventional involute gears.

 

[mfgenggear]

OP
Wire cnc would be more precise

Cycloidal Gear Calculator

 

[Doug Hunter]

How many units are involved in prototype and production? If you need > 100, then Powder Metallurgy becomes a good option to consider, as you'll be near the breakeven point for tooling cost. Wire EDM is also a process to consider in low volume (perhaps that's what Mfgenggear meant by 'wire CNC').

 

[maximumcoolbeans]

Thanks for the suggestions!

@mfgenggear That calculator appears to be for pairs of cycloidal gears but the type of gear that I'm interested in is a bit different: https://en.wikipedia.org/wiki/Cycloidal_drive.

 

[mfgenggear]

In 30 years plus I never in countered cycloidal gears for gear box application, and never seen it used in automotive and motorcycle applications. Don't know.
But conventional involute gears work for high torque. And rpm aerospace application with very high horse power. Just saying.

 

[maximumcoolbeans]

I suggest you do a bit of reading about cycloidal drives if you're unfamiliar with them (see the wiki link above).

 

[Doug Hunter]

Cycloidal drive: very interesting... I did not know about these.

 

[mfgenggear]

OP
I am sure cycloidal gearing has its use.
Just like harmonic drives . And is an other bag of tools for the designer. What meant to add, and suggest it's not as common. As involute gearing.

 

[Doug Hunter]

I'm likewise sure that involute gearing is much more widely used. The Cycloidal Drive appears to have the advantage of large gear reductions with lower gear count and space. I think that traditional involute gearing would require a couple stages of planetary systems to get this kind of reduction. I'm also wondering now if there's a way to implement the same orbiting principle as the Cycloidal Drive except with involute gears instread of cycloidal?

 

[mfgenggear]

Harmonic drives also have a high reduction and are used in robotics. Very low back lash and precise movement and are as well very good. Except at low rpm.
Cycloidal gear to my knowledge have the same issues. Very good at low RPM with high reduction.

 

[maximumcoolbeans]

@Doug Hunter This video touches on that topic of involute vs cycloidal teeth in a cycloidal drive:

From this paper: "In an ideal cycloidal drive, all roller pins contact the cycloidal gear, and about half the roller pins bear the load." I'm not sure if this distributed load bearing is possible with involute teeth. It seems like cycloidal teeth are important for acheiving the low backlash, low noise, and high impact resistance of cycloidal drives. But I would like to learn more about this topic and about other possible tooth profiles in cycloidal drives.