eliptical gear

[ediushu]

It might sound stupid but since I am not an expert in gears I want to ask you guys: There is any way to built an eliptical gear or any other form except a circle which can allows me to have a varaibale speed when this gear is meshing with a pinion? Don't worry about machining, it will be a plastic part.

 

[Pekelder]

Not such a stupid question. It is possible, but the problem will be how to control the distance between the two axis, because they will will change during rotation if you use an eliptical gear and a normal pinion.

http://www.sherline.com/names01.htm

(about halfway down there's an example of two eliptical gears. They actually work, the distance is constant).
You van even have square gears! McGrawHill, "Mechanisms&Mechanical Devices Sourcebook", Nicholas P. Chironis gives more examples.
You migt considder a four-bar-linkage though, simpler to make, and easier to adapt if you want to change the ratio.

http://iel.ucdavis.edu/design/fourbar/

Regards,

Pekelder

 

[chicopee]

About 20 years ago elliptical sprockets were being introduced into bicycle design as it was claimed that it reduced strain on the legs of bicyclists. I eventually saw such sprockets and the aspect ratio of major to minor axis was close to one.
An elliptical gear must mesh w/ another elliptical gear for two fixed centers of rotation; however they must be positioned so that major axis of one gear is in line w/minor axis of the other gear for the system to work.