Designing things that use gears

I was wondering - how does one go about designing something that involves various gears? What are the principles behind the size/shape/etc.

If I wanted to design my own motor-powered eggbeater (for example) what kind of principles would I need to know to convert the turning of the motor to the turning of the whisks?

 

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Shape: gears are usually round.

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Size: never use an even-numbered (i.e. even number of teeth) gear wheel (in fact they're usually non-standard from most manufacturers).
After that you just pick the ones that
A) give the ratio you require and
B) are closest to 19 or 21 toothed wheels (they're usually cheaper).

Edit: and try not to go below 15 teeth - wheels that small usually run raggedly.

Simple: motor RPM x driver gear/ driven gear = output rpm.
If you know the motor speed and the desired rpm of the whisk then just choose the wheel pair to obtain that ratio.

 

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If you build a large mixer you could use a simple belt and pulley design, thats always a smart place to start when you are learning gearing. I started learning this stuff messing with lawnmowers.

Also you can get high speed motors that wouldn't require much gearing at all.

 

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That's interesting. I wonder why odd-numbers of teeth are preferred. It doesn't seem like it would matter, but I guess it does in certain designs.

Yes that's all there is to it, unless torque is a concern. For torque, change your equation to:

motor torque / (driver gear/ driven gear) = output torque

...

I wonder if there are any kits available which allow various gears to be combined and tested, (like the old "erector sets")?

 

It matters in all designs - an even number of teeth puts the same tooth in the same "position" with each and every turn. If there's a tight fit/ bad match then that tooth will wear unevenly. An odd number of teeth will not repeat that "fit" on every turn but only after a number (depending on the exact ratios of teeth) of turns.

Um, why do you need a test? You don't trust a simple equation?

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I'd imagine something like Lego Technics would have something that would do the job of "testing".

 

I guess that makes sense, if the idea is to limit the number of times that two particular teeth are engaged with each other. This seems to be a preventative measure in case one of the teeth is slightly different than the rest.

But on the other hand, what if you are building something like a clock, and you need exactly 12:1 ratio? With odd numbered teeth, that seems like it would be problematic?

I thought a kit might be neat for my girlfriend's kids to play with. I guess buying some gears and mounting them in various combinations might amount to the same thing. Maybe put a little hand-crank on there, or something.

I'll look into the Lego Technics. Thanks!

 

Trust me, just finding the right size of motor is all you need for an eggbeater. No need to have mechanical advantages here. The only gears would be beveled with a tooth ratio of unity. It's practical economics.

Keep all gears lubricated with silicone oil.