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# Need Help on Orrery gears Answered

Hi,
I'm planning on building an orrery and I need some help. I've been doing some research on instructions on how to build one. The main thing that I'm not completely understood with is the gears and how they actually work. I know a bit about some basic principles of gear ratios and stuff but not like the actual mechanism (ps i like to look at diagrams). I'm also planning on making 9 planets (i mean 8 + pluto and the moon and the sun). Any help would be appreciated, thanks!

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https://www.instructables.com/id/Orrery-a-Mechanic-Solar-System-Model-Designed-for-/

Not the best idead to use this as a first project if you have no clue about gears, how to make or how to use them correctly.
Start making your own gears and simple mechanisms before attempting to copy the solar system.
If you want it to be precise then you either need to do proper research and buy the required gears or you have to make them yourself - both requires decent understanding of what you are doing.

I did some research and came up with this:

This is a plan for my prototype, when the crank turns, it turns the gear on the sun shaft, which turns the earth gears and the moon gear. (The rectangles with an arrow indicates that it is a gear with the direction of rotation). The sizes are not to scale.

This should in theory work I guess, I would like to hear some feedback.

Also, I'm trying to figure out gear ratios for the planets, especially those that are far from the sun since they barely move (e.g. Saturn, Neptune). If anyone can help me calculate those ratios while having a relatively small error percentage then that would be great.

Why not check some images online or visit your local museum?
Should be simple enough to find some examples how this was done before we had computer.
And if accuracy is no real demand anyway why not use belts and pulleys?
Much easier than gears.
The info on the rotation speeds can be found through Google and Wiki.
Check how long the planets need to get around the sun - this gives you the ratios.
Same story for their moons just base it on the speed of the planet instead of the sun.

Thanks for the advice! I went with gears since I want it to be kind of accurate.

So onto the gear ratios, I've been trying different ratios that are relatively close to the original one and also less teeth. However still when I get to far objects like Neptune and Charon, the ratio is so large that a lot of teeth are needed. One question that I couldn't find the answer for is figuring out gear ratios when I'm using multiple compound gear trains. It would be great if someone can enlighten me on that.