CR4® - The Engineer's Place for News and Discussion®

 Previous in Forum: Bed Material Next in Forum: Obtain Saturated Air from Unsaturated Air Without Adding Any Moisture
Associate

Join Date: Mar 2017
Posts: 48

# Gears

05/28/2017 8:51 AM

I have been studying gears and there is this law of gear ratios that say that small diameter gears when rotated 2 times , then the large diameter gear rotates one time. (Assuming 2:1 ratio). but if we are using big diameter gear as drive gear and using to rotate small diameter gear, then torque should be decrease as RPM or speed of the small diameter gear is increasing. But if the Torque is decreasing then how can small diameter gear rotates faster than the big diameter gear. Because to rotate anything faster, is not torque is being given to the small diameter gear even though we say that torque is decreasing. Help me clear this confusion.

Pathfinder Tags: gears Gears ratio speed torque
Interested in this topic? By joining CR4 you can "subscribe" to

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
4
Guru

Join Date: Apr 2012
Location: Detroit MI, USA
Posts: 2165
#1

### Re: Gears

05/28/2017 9:13 AM

Have you ever looked and the sprockets on a bicycle? Same principle. The larger one at the crank turns the smaller one at the wheel.

There does need to sufficient torque but it's not that big of a deal.

To further your studies, I suggest you get a multiple speed bike (mountain bike), turn it upside down and turn the crank with your hands. change the gears and you will feel and see the difference.

Put the crank on it's smallest gear and the wheel on it's largest gear. Very easy to pedal but not much speed. Work your way through them until you have the wheel on it's smallest gear and the crank on it's largest one. Very hard to pedal but much more speed. You will feel the increase of torque needed and see the speed increase but it works.

__________________
How we deal with death is at least as important as how we deal with life. --CAPTAIN KIRK, Star Trek II: The Wrath of Khan
Associate

Join Date: Mar 2017
Posts: 48
#2

### Re: Gears

05/28/2017 9:28 AM

yeah but imagine a system which is made up of three gears. Let us say Gear A which has 36 teeth, Gear B which has 24 teeth and Gear C which has 12 Teeth. Now here Gear A is the Drive gear. Assume we have connected the Gear A with a motor which rotates the Gear A at 60 hz. the others gears are at rest and when this Gear A starts to rotate, then The others Gears starts rotating. And that too faster than the Gear A. ( due to gear ratio). As the Gear B and C are rotating, should not there be a torque to rotate them and as they are rotating faster should not be the torque greater then the Drive gear which in this case is Gear A? Because they are rotating from rest, so torque should be big than that of Gear A because they are rotating faster and to rotate faster torque is needed. I am confused.

4
Guru

Join Date: Apr 2012
Location: Detroit MI, USA
Posts: 2165
#4

### Re: Gears

05/28/2017 11:34 AM
__________________
How we deal with death is at least as important as how we deal with life. --CAPTAIN KIRK, Star Trek II: The Wrath of Khan
Associate

Join Date: Mar 2017
Posts: 48
#5

### Re: Gears

05/28/2017 11:59 AM

Wow bro thanks a lot . You have helped me so much . Thanks a lot really thank you . The references has helped a lot . Thanks bro. Thanks a lot .Thank you .

Off Topic (Score 5)
Guru

Join Date: Apr 2012
Location: Detroit MI, USA
Posts: 2165
#6

### Re: Gears

05/28/2017 1:12 PM

A simple, single thank you would have done unless you are being sarcastic.

If you are not, then you are welcome.

__________________
How we deal with death is at least as important as how we deal with life. --CAPTAIN KIRK, Star Trek II: The Wrath of Khan
Off Topic (Score 5)
Associate

Join Date: Mar 2017
Posts: 48
#7

### Re: Gears

05/28/2017 1:19 PM

no really mate. Thanks a lot. I have been working on this project for since a long time. Its about this machine i am developing. And mathematical model is quite worrisome to me as i was having difficulty to understand this. Thank you. I am not being sarcastic.

Off Topic (Score 5)
Guru

Join Date: Apr 2012
Location: Detroit MI, USA
Posts: 2165
#8

### Re: Gears

05/28/2017 1:29 PM

Then I am glad to have helped you.

I only said that because sometimes it's hard to get a single thank you when you help somebody out here. When you get 5 or 6 at once, it's hard to know what to think.

__________________
How we deal with death is at least as important as how we deal with life. --CAPTAIN KIRK, Star Trek II: The Wrath of Khan
Off Topic (Score 5)
Guru

Join Date: Aug 2005
Posts: 4214
#10

### Re: Gears

05/29/2017 8:58 AM

Not sure if this helps, but: work = force times distance

Your understanding of the gears only takes into account the speed (distance/time) it is not taking into account the load on the secondary gear.

Imagine that the axle of the secondary gear is being used to, say, lift a bucket in a well. If the bucket is empty you will get away with a large A gear and a small B gear and the bucket will move fast; but if the bucket is full of gold then you will need a small A gear and a large B gear, you will be able to produce much more force but the bucket will move very slowly.

__________________
We are alone in the universe, or, we are not. Either way it's incredible... Adapted from R. Buckminster Fuller/Arthur C. Clarke
Associate

Join Date: Mar 2017
Posts: 48
#11

### Re: Gears

05/29/2017 11:34 AM

Well what if there is not load present on it. A simple gear train . And also what type of gears should be used if the rpm is in the range of 10000 Hz. Any idea how much heat it will produce ? And if we use sprocket to reduce the heat ? Any idea ?

Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26894
#14

### Re: Gears

05/30/2017 9:03 AM

<...what if there is not load present on it...> If there were no load on it then there would be no torque applied to the motive unit other than that developed as a result of whirling gears. Then, why would one do that (rhetorical question - NNTR)? It makes sense to turn the thing off.

<...if the rpm is in the range of 10000 Hz...> A shaft speed of 600,000rpm is a bit excessive for currently-engineered systems. Such a region would be new technology, in which case the original post is describing leading-edge, pioneering research. <...Any idea how much heat it will produce ?...> Absolutely no idea, it being pioneering research done by others.

The question <...use sprocket to reduce the heat ?...> holds no meaning here.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Associate

Join Date: Mar 2017
Posts: 48
#16

### Re: Gears

05/30/2017 12:03 PM

Yeah my bad there . Sorry . Its not Hz but RPM. 10000 RPM. Then can you tell me ? Thanks a lot by the way . And about the load thing . Don't worry it is still useful . Thanks again but . Thanks

Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26894
#17

### Re: Gears

05/30/2017 12:09 PM

Start from the beginning again. What is the objective?

"Provide a facility that does the following:..........." is a good start.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Associate

Join Date: Mar 2017
Posts: 48
#18

### Re: Gears

05/30/2017 12:20 PM

Its research part . The whole objective is. Can not disclose to you about it . But still thanks for taking your time out and help me. I appreciate that .

Off Topic (Score 5)
Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26894
#19

### Re: Gears

05/30/2017 4:35 PM

OK. Good luck with it.

<unsubscribes>

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Guru

Join Date: Apr 2010
Posts: 5901
#3

### Re: Gears

05/28/2017 9:51 AM

The little gear, due to friction, needs a certain amount of torque to rotate the speed that it is rotating. You will have to apply twice as much torque to the big gear to drive the little gear plus whatever torque is needed to overcome the friction of the big gear turning.

2
Guru

Join Date: Apr 2012
Location: Detroit MI, USA
Posts: 2165
#9

### Re: Gears

05/28/2017 1:38 PM

If you need more info on this, google "gear ratio vs. torque". Lots of stuff out there.

__________________
How we deal with death is at least as important as how we deal with life. --CAPTAIN KIRK, Star Trek II: The Wrath of Khan
Associate

Join Date: Mar 2017
Posts: 48
#12

### Re: Gears

05/29/2017 11:35 AM

Yeah thanks bro.

Guru

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting ["brexit" - ugh] as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26894
#13

### Re: Gears

05/30/2017 4:52 AM

Shaft torque is something presented by the load to the motive equipment. Torque multiplied by angular velocity is power.

As energy is conserved, any change in shaft speed in a mechanism such as a gearbox is accompanied by almost a reciprocal change in shaft torque. However, there will be losses as correctly indicated.

It is not possible to say with certainty how much heat will be lost in a gearbox other than the power on the output shaft, measured by torque multiplied by angular velocity, will be smaller than that on the input shaft, and the difference between the two will be the heat liberated. Good design and maintenance with proper lubrication can keep this to a minimum.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Anonymous Poster #1
#15

### Re: Gears

05/30/2017 10:26 AM

Interested in this topic? By joining CR4 you can "subscribe" to