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Old Dec 16, 2005, 11:52 PM
Registered User
North Pole, Alaska
Joined Nov 2005
41 Posts
NEED help figuring out gear ratio

The motor came with gears part of a ARF kit I bought, the plane has taken a dirt nap and the motor, esc and batt are looking for a new ride so I thought making the little 180 a direct and putting it on a wing design.
I don't know what the gearing is there aren't any numbers on the gears or letters I marked the big one and small one and rotated them to see how many turns til they meet back.
The small one makes 4.5 turns to make the big one do one complete turn. the small one has 10 teeth and the larger one is either 44 or 43. Not sure how to figure out the gears. Any help would be good. Also how do you tell what the numbers are on gears like 6:6:1.
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Old Dec 17, 2005, 12:17 AM
Or am I...
Bournemouth, Dorset, UK
Joined Jan 2005
2,460 Posts
well to figure out gears you simply write how many times it takes to do 1 rotation, so a gear that takes 4,5 turns to turn the other gear once is 4,5:1.

and about the help you need im summeriseing that you have a 180 motor?? and no gearbox?? its a bit unclear of what you want
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Old Dec 17, 2005, 01:49 AM
Use the Force!
LBMiller5's Avatar
San Marcos, CA
Joined Jan 2005
2,179 Posts
Saylorms,

All gears ratios are calculated by counting the number of teeth on one gear (the larger one), and dividing it by the number of teeth on the other gear (the smaller one).

For example, if you have a 10 tooth pinion gear on the motor, and a 43 tooth gear on the output shaft, then the ratio is 43/10 which is 4.3:1.

If you have a 12 tooth pinion gear on the motor, and a 80 tooth gear on the output shaft, then the ratio would be 80/12 or 6.66:1

If the gear is not marked, you can count them yourself. The way I do it is to take a fine point Sharpie pen and color the side of one gear tooth. This will be your starting point, and I call it tooth #1. Next I count around the gear and put a small mark on tooth #10, #20, #30 and so on, so if I mess up a count, I don't have to start over. Continue on around the gear until you get back to the initial tooth, but don't count it again! Then you know how many teeth the gear has, and you can write this number on the back with the Sharpie pen.

There are many gear combinations that can give the same ratio. For example, if you had a 10 tooth pinion and a 40 tooth output gear, the ratio is 4:1. A 12 tooth pinion with a 48 tooth output gear also has a ratio of 4:1, since 48/12=4. Likewise a 15 tooth pinion with a 60 tooth output gear would also have a 4:1 gear ratio, so there are an infinate number of combinations. The only way to tell the gear ratio is to count the gear teeth and divide them to get the ratio.

That should answer your question.

Lucien
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Old Dec 18, 2005, 02:47 AM
Registered User
North Pole, Alaska
Joined Nov 2005
41 Posts
thanks for the input guys, yes it would be 4:3:1 ratio and it was on a 180 motor I got with a kit. Just trying to see if the combo would work on a little wing that I'm looking at getting or if I'd need to go direct drive with a smaller prop. It's turning a EMI 8.5 X 8.0
Just toying with it like to put it to use since I've already got all the hardware.
Once xmas gets here I'm sure I've got some upgrades sitting under the tree
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