Author Topic: Gear Ratio needed  (Read 3210 times)

Offline KKC

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Gear Ratio needed
« on: March 14, 2016, 11:17:34 AM »
Okay... If I wanted to add a dial that would show AM or PM.  ie. Sun and Moon. what would my gear ratio be? 

Offline steve323

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Re: Gear Ratio needed
« Reply #1 on: March 15, 2016, 08:58:34 AM »
Hi KKC,

This sounds like a great addition to a clock to add some additional flair.

Adding an AM/PM indicator sounds easy.  Just divide the hour hand by 2.  One way would be to attach 2 gears to the hour hand gear.  This would typically be 30 or 32 teeth.  Use an 8 tooth intermediate gear to drive a 16 tooth gear that will rotate once every 24 hours. 

I searched for moon dial gear ratios.  The moon phase is 29 days 12 hours 44 minutes and 3 seconds.  This is typically rounded off to 29.5, which will leave an error of one day every 32 months.  This is definitely within the tolerances of the wooden clock accuracy. 

A classic moon phase dial has 2 moons on it and needs to rotate half way around every 29.5 days, or once per 59 days.  Since the hour hand rotates 2 times per day, the gear ratio needs to be 118:1 relative to the hour hand.  Alternatively, it could use a 59:1 ratio relative to the AM/PM indicator that rotates once per day.

A 59:1 ratio can be done with 2 gear sets.  Add an 8 tooth gear to the AM/PM indicator to drive a 59 tooth gear.  This will rotate 8 times per 59 days.  Add an 8 tooth gear driving a 64 tooth gear to divide again by 8X. 

Steve

Offline steve323

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Re: Gear Ratio needed
« Reply #2 on: March 15, 2016, 12:54:08 PM »
I can't stop thinking about the gearing for the moon phase.  According to Google, the exact lunar phase is 29.5305888531 days.  The desire is to have a phase dial with 2 moons, so a gear train needs to be devised that will divide by 4 times 29.53... = 118.1235541.

Let's also assume that we want to divide by 118.1235541 with 2 sets of gears and the minimum teeth per small gear is 8.  We need a gear ratio of 1:118.1235541.  Multiplying both sides by 64 would result in a ratio of 64:7559.907.  Round this off to 64:7560.  The number of teeth in all the small gears is 64 which is derived using 2 8 tooth gears.  We need to find the divisors for the big gears that multiply to 7560

7560 is equal to 2^3 * 3^3 * 5 * 7.  One way to divide this among 2 gears is 2^2 * 3 * 7 and 2 * 3^2 * 5.  This would be an 84 tooth gear and a 90 tooth gear.

So one good gear ratio would be 8:84 followed by 8:90 running directly from the hour hand.  This would produce a divide ratio of 118.125, corresponding to a lunar cycle of 29.53125 which is fairly close to the exact target.  I calculate this to be an error of one day per 126 years.

Steve

Offline KKC

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Re: Gear Ratio needed
« Reply #3 on: March 15, 2016, 01:17:22 PM »
And thus this is why I asked you what the ratio would be.  I still have no clue how you come up with those numbers and how it all goes together but these are the things I think about for my clock.  I hadn't thought of a lunar clock that's pretty cool... But still... I think of ways to add more that just hours and minutes.  I wonder if you could do days too?  Didn't Clayton do one with days? and then just bring them all together into one major automated clock.  How cool would that be... Of course I'm beginning to believe you'd have to have some sort of electric motor to drive it. With friction and inertia and god knows what else I'm missing going into it, weights just seem overwhelming. 

Offline steve323

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Re: Gear Ratio needed
« Reply #4 on: March 15, 2016, 03:15:19 PM »
I agree that it is desirable for wooden clocks to do something additional.  It was fun doing the calculations for the lunar dial.  These gears would rotate at such a low speed that they would require very little additional energy.  But quite frankly, we have a traditional grandfather clock with a lunar dial and I never even notice where it is pointing.

I had a wind up wrist watch as a kid with a date indicator.  It only counted to 31, so it needed to be reset at the end of 5 months of the year.  I recall having to advance the time by 24 hours at the end of those months.  February would require adding 48 or 36 hours.  A clock that knows the exact days per month would be really cool, but much more complicated than simple gearing.

Steve

Offline KKC

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Re: Gear Ratio needed
« Reply #5 on: March 16, 2016, 08:40:44 AM »

Just divide the hour hand by 2.  One way would be to attach 2 gears to the hour hand gear.  This would typically be 30 or 32 teeth.  Use an 8 tooth intermediate gear to drive a 16 tooth gear that will rotate once every 24 hours. 

Steve

Okay so I would need 1 - 8 tooth gear and 1 - 16 tooth gear? I'll play with it on the Gear Generator.

Offline steve323

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Re: Gear Ratio needed
« Reply #6 on: March 16, 2016, 12:38:43 PM »
The starting point for the AM/PM indicator is the hour hand that rotates once every 12 hours.  My thought process was off slightly.  What you need to do is join an 8 tooth gear to the hour hand so it also rotates once every 12 hours.  If this 8 tooth gear drives a 16 tooth gear, it will rotate once every 24 hours.  It will rotate counter-clockwise, so an intermediate gear of any size between the 2 stages would reverse the direction to clockwise. 

Alternatively, you could just use a gear with twice as many teeth as the hour hand gear.  It would be driven by the same gear that drives the hour hand, but will rotate at half the rate because it has twice as many teeth.

The output of the AM/PM indicator could drive a small dial with 24 ticks, marked from 1-12AM and 1-12PM. 

Steve

Offline KKC

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Re: Gear Ratio needed
« Reply #7 on: March 16, 2016, 02:20:56 PM »
Okay now it's starting to make since... Man am I thick... LOL...

Offline KKC

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Re: Gear Ratio needed
« Reply #8 on: March 22, 2016, 11:06:42 AM »
Got to thinking about this Steve.  I don't think I would want the Am - Pm dial to go clockwise.  If the clock is on the north wall the dial would need to rise from the right and go to the left.  Counterclockwise right?

Offline steve323

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Re: Gear Ratio needed
« Reply #9 on: March 23, 2016, 09:04:58 AM »
That's a fairly cool idea KKC.  It would be like a mini orrery.  All you would need is a simple 2:1 gear ratio.  Add an 8 tooth gear to the hour hand and let it drive a 16 tooth gear.

Steve

Offline KKC

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Re: Gear Ratio needed
« Reply #10 on: March 24, 2016, 06:08:57 AM »
An 8 tooth pinion to the hour wheel and a 16 tooth wheel to the sun and moon dial? Correct?
« Last Edit: March 24, 2016, 12:54:34 PM by KKC »

Offline KKC

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Re: Gear Ratio needed
« Reply #11 on: March 24, 2016, 02:20:57 PM »
I'm working on what my dial will look like... I'll post it once it get it finished.

Offline panistefanin

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Re: Gear Ratio needed
« Reply #12 on: June 05, 2017, 08:02:25 AM »
I'm new and I'm interested in this topic. Thank you!
mybestwestern