Planetary gear train calculations

[MarkH111]

Hello,

I am designing an orrery (a mechanical model of of the solar system), im a geotechnical engineer by trade so I'm not fresh on calculating more complex gear ratios.

I have a system within the orrery where I want to reduce 365 rpm to 13.36rpm. I can rationalize 13.36 to 334/25 teeth in one stage, but 334 teeth is too great a circumference for the size of orrery I'm building. So I wanted to use a planetary reduction drive with a fixed outer ring gear to step the ratio down. Is it possible to calculate the specification of a planetary reduction drive, that being the number of teeth on the respective gears (sun gear, the three planetary gears and the outer fixed ring gear) to give the same output on the planetary cluster as the one stage 334/25 (I.e. The three planetary gears rotate at 13.36 rpm) I have determined above? Ideally I'm looking for a formulaic approach to this. Many of the examples of planetary gear train calculations already know the number of teeth on one or more gears in the system; as I am designing from scratch and machining the components I do not.

Also does anyone know of some reasonable accessible software that would allow the design of gears and compound gears in 3d?

Many thanks,

 

[3DDave]

Check

http://www.gearotic.com/

for design and visualization software.
The related videos are at

https://www.youtube.com/user/ArtFenerty/videos

A lot of concentration on clocks.