My series of educational mechanical examples

This model is one of my educational mechanical device examples, which uses an 80 mm x 80 mm base plate.
You can find all the models of this series in this collection =>[Example of mechanical devices]

 

This model

This is an educational model of a flexible wave drive system

 

Brief explanation

In this model, the outer ring gear has 40 teeth, and the inner flexible gear has 38 teeth. The flexible gear is deformed into an oval shape by two rotating discs that press from the inside out, allowing the teeth near the long axis to engage with the ring gear, while the teeth near the short axis are completely avoided.

 

Due to the different number of teeth on the two gears, their tooth meshing will gradually shift as you move away from the contact area of the long axis. When the disc rotates, the long axis of the ellipse also rotates, causing the meshing area to move around the gear. After the disc completes a half-turn rotation, the difference in the number of teeth causes the flexible gear to rotate back exactly one tooth; after completing a full turn rotation, it rotates back two teeth. Therefore, the reduction ratio from the input knob to the output flexible gear is 2:38, or

 

For this model, I used a standard involute tooth profile, but I want to know which tooth profile is most suitable for this gear system.

 

This kind of institution is different from the ones we introduced earlier.Planetary speed reduction gear systemThere are significant similarities. In both cases, two gears with slightly different numbers of teeth only engage each other at a few points around their perimeters. When these engagement points complete a full rotation, the free gear rotates backward precisely relative to the fixed gear, with the amount of rotation equal to the difference in the number of teeth.Cam-and-follower drive systemI also shared a similar concept.

Related models

 

Shell

This model is included in theThe shell in my first set is compatible。

Print

• Use a name called???-printable.stlPrint the model。
  Name:???-assembled.stlThe model is only used to demonstrate its assembly method.
   
• UseA fully dried PETGIn order to achieve better dimensional accuracy and sufficient flexibility.
• UseA layer height of 0.1 mm or 0.08 mm, in order to obtain a smoother surface.
• Use a slower printing speed for the overhanging parts.
• Choose"Random" seam positionTo achieve a smoother rotation.
  The randomly distributed seams should be easy to smooth out after some wear and tear. Print
   
• Flexible gears must be usedPETGPrinting, usingGenerating a standard wallThe method results in a line width of less than 0.4 millimeters.a line width of 0.3 mmIt works very well for me. Check whether the wall of the part is exactly two lines thick at its thinnest point. Please note that PETG is more elastic than PLA.

Polishing and filing

Please note that in this model, the rotation of the bearing base is deliberately designed to be not very smooth.

Sometimes, the gears are affected by the drawing effect and/or the elephant's foot effect, resulting in a too-tight fit with the shaft

If the surface of the shaft is rough due to the drawing effect, please use a small piece of sandpaper to polish off the rough parts.

If you think the gear can't rotate smoothly due to the elephant's foot effect, please use a fine round file to slightly widen the hole.

If there are no such problems, the parts should rotate very smoothly with minimal friction.

 

Assemble

Fix the parts with clamp rings.

 

Update

• April 26, 2026, version 154
  • Reduce the thickness of the flexible wall to 0.4 mm to achieve greater flexibility and smoother rotation.

Other examples

You might also be interested in the models in my examples of educational mechanical devices.

Search for it in this collection:
https://makerworld.com/collections/15048577-my-educational-mechanism-models

 

Have a nice printing experience!

Acknowledgments

I owe my interest in gears to someone.K. SuzukiA wonderful article andYouTube videoMany of the institutions showcased in this series come fromHis websitethe introduction on it. He also made it himself.An excellent gear modelIf it weren't for his inspiration, this series wouldn't exist.

I'm fromHaguruma-No-Hanashi WebsiteI've learned a lot of technical details about gear tooth design. I'm very grateful for that.

 

Permission

• The 3D model is based onCreative Commons Attribution 4.0 International License AgreementAuthorization.
• However, the text and images on this page are copyrighted.