R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric On-Road

Reply
 
Thread Tools Search this Thread
Old 08-05-2009, 12:56 AM   #1
Tech Adept
 
ep10's Avatar
 
Join Date: Feb 2008
Posts: 199
Trader Rating: 13 (100%+)
Default Gear ratio question

I have a gear ratio question. Sorry I am a novice, please correct me if I am wrong.

First, let's forgetting about the track condition, track length, just imagine it's average for everything.

I want to confirm that, is that a lower gear ratio (e.g 6:1), will provide more top-speed? And higher gear ratio (e.g. 9:1) will provide more torque?

What's the different running on a low gear ratio (e.g. 6:1) between a 17.5 and 13.5 motors (on the same car)? How actually the car will react differently?

Thanks!
ep10 is offline   Reply With Quote
Old 08-05-2009, 01:11 AM   #2
Tech Elite
 
sosidge's Avatar
 
Join Date: Dec 2001
Location: Bristol, UK
Posts: 3,865
Default

6:1 would have as higher top speed than 9:1. Although we actually call 6:1 a "high" ratio and 9:1 a "low" ratio.

Run a 17.5 on the same ratio as a 13.5 and you will have lower top speed (Assuming the 17.5 has fewer RPM and less power, which is normally the case).
sosidge is offline   Reply With Quote
Old 08-05-2009, 01:33 AM   #3
Tech Elite
 
niznai's Avatar
 
Join Date: Feb 2009
Location: All over the place
Posts: 2,940
Default

Quote:
Originally Posted by ep10 View Post
....
I want to confirm that, is that a lower gear ratio (e.g 6:1), will provide more top-speed? And higher gear ratio (e.g. 9:1) will provide more torque?

What's the different running on a low gear ratio (e.g. 6:1) between a 17.5 and 13.5 motors (on the same car)? How actually the car will react differently?

Thanks!
Yes.
Think of the gear ratio in terms of how many turns one gear makes to get the next (the one it meshes with) gear to turn once. That means of course for the first gear ratio you need to turn the input gear six times to turn the output gear once whilst for the second gear ratio you need the input gear to turn nine times to have the output gear turn once. By now it should be clear that once your input gear reaches its top rev count the output gear will turn six times slower (for the first gear ratio) or nine times slower (for the second gear ratio). Guess which would give you a higher revcount then between the two!

About torque, the problem is a little bit more difficutl to explain. One way to look at it is this. A higher gear ratio means a higher difference between gear diameters (or radii). The radius of your spur is the lever your force is acting upon. Elementary physics tells us that the longer the arm the force is acting upon, the more torque it has (t=FxR). Think of a breaker bar you would use to undo a stubborn bolt. The more stubborn, the longer the breaker bar you'd use. That's because it gives you more torque. Same law applies here.

There are also other considerations to do with gear mesh cinematics and efficiency, but we'll stop here.

For the second question, your car will accelerate slower with the less torquey motor (which it is difficult to say which one it is with brushless as there are very many variables). All else being equal lower wind motors have less torque, so to gain some of it back you need to run higher gear ratios.

That being said, if you break traction, your wheels will spin crazily with a lower turn motor sooner than with a higher turn (assuming gearing is kept the same). This is a constant danger with low turn motors because they can break traction very easily. All you need is to unload a wheel in a turn and voila! Instant spinout. Solution is to have good tires and gear appropiately.

But this is not all there is to it.

Still awake?
__________________
Team Greasy Weasel

The best upgrade to any car is some driver skill.
niznai is offline   Reply With Quote
Old 08-05-2009, 01:00 PM   #4
Tech Adept
 
ep10's Avatar
 
Join Date: Feb 2008
Posts: 199
Trader Rating: 13 (100%+)
Default

Thanks folk!

Although I understand the simple concept of gear ratio (such as 6 turns of pinion makes 1 turn of spur... etc), I am still confused about the way of saying....

So.... for examle, 6:1 is calling "high" ratio, while 9:1 is calling "low" ratio???
ep10 is offline   Reply With Quote
Old 08-05-2009, 01:02 PM   #5
Tech Adept
 
ep10's Avatar
 
Join Date: Feb 2008
Posts: 199
Trader Rating: 13 (100%+)
Default

Is that the 13.5 has higher rpm than 17.5, which results in a faster motor???

If I had 2 identical cars:
car 1) running a 13.5 with gear ratio 8:1
car 2) running a 17.5 with gear ratio 6:1

(of course, the ratio is just some assuming number),

Would the car 2 has a chance to be equal speed as (or faster than) car 1??
ep10 is offline   Reply With Quote
Old 08-05-2009, 01:13 PM   #6
Tech Adept
 
ep10's Avatar
 
Join Date: Feb 2008
Posts: 199
Trader Rating: 13 (100%+)
Default

Quote:
Originally Posted by niznai View Post
For the second question, your car will accelerate slower with the less torquey motor (which it is difficult to say which one it is with brushless as there are very many variables). All else being equal lower wind motors have less torque, so to gain some of it back you need to run higher gear ratios.
For application, it means, while using a 17.5 (<== low wind motor), to gain some torque back so need to run a higher gear ration (<== something like 5:1, 6:1.... etc)???

Am I having a wrong equation??

I think, 17.5 with 6:1, will have more top-speed, then 17.5 with 9:1..... I am confused again.


Quote:
Originally Posted by niznai View Post
That being said, if you break traction, your wheels will spin crazily with a lower turn motor sooner than with a higher turn (assuming gearing is kept the same). This is a constant danger with low turn motors because they can break traction very easily. All you need is to unload a wheel in a turn and voila! Instant spinout. Solution is to have good tires and gear appropiately.

But this is not all there is to it.
Please sorry for the novice dumpS, (<=== that's me ) While you mentioned lower turn and higher turn motor, what are they refering to? Coz for my understanding, in brushed 9T called a lower turn, 27T is higher turn???? (I dunno if this is correct or not).

And then, in brushless, 3.5 is higher or lower, compared to 13.5???

Please give me some lessons....

Thank you very much.
ep10 is offline   Reply With Quote
Old 08-05-2009, 02:26 PM   #7
Tech Elite
 
sosidge's Avatar
 
Join Date: Dec 2001
Location: Bristol, UK
Posts: 3,865
Default

Quote:
Originally Posted by ep10 View Post
Thanks folk!

Although I understand the simple concept of gear ratio (such as 6 turns of motor makes 1 turn of wheel... etc), I am still confused about the way of saying....

So.... for examle, 6:1 is calling "high" ratio, while 9:1 is calling "low" ratio???
Corrected.
sosidge is offline   Reply With Quote
Old 08-05-2009, 02:28 PM   #8
Tech Elite
 
sosidge's Avatar
 
Join Date: Dec 2001
Location: Bristol, UK
Posts: 3,865
Default

Quote:
Originally Posted by ep10 View Post
Is that the 13.5 has higher rpm than 17.5, which results in a faster motor???

If I had 2 identical cars:
car 1) running a 13.5 with gear ratio 8:1
car 2) running a 17.5 with gear ratio 6:1

(of course, the ratio is just some assuming number),

Would the car 2 has a chance to be equal speed as (or faster than) car 1??
No chance of equal speed, the 13.5 generates more power. Even if you gear for the same top end the 13.5 will have more acceleration.
sosidge is offline   Reply With Quote
Old 08-05-2009, 03:48 PM   #9
Tech Adept
 
ep10's Avatar
 
Join Date: Feb 2008
Posts: 199
Trader Rating: 13 (100%+)
Default

Quote:
Originally Posted by sosidge View Post
No chance of equal speed, the 13.5 generates more power. Even if you gear for the same top end the 13.5 will have more acceleration.
In term of acceleration, same motor with low ratio (9:1) will be better than high ration (6:1)???
ep10 is offline   Reply With Quote
Old 08-05-2009, 08:05 PM   #10
Tech Elite
 
niznai's Avatar
 
Join Date: Feb 2009
Location: All over the place
Posts: 2,940
Default

Quote:
Originally Posted by ep10 View Post

I think, 17.5 with 6:1, will have more top-speed, then 17.5 with 9:1..... I am confused again.




Please sorry for the novice dumpS, (<=== that's me ) While you mentioned lower turn and higher turn motor, what are they refering to? Coz for my understanding, in brushed 9T called a lower turn, 27T is higher turn???? (I dunno if this is correct or not).

Theoretically yes (practically there are other factors that may affect the top speed), but OK, let's say yes.

Don't confuse yourself. There is no "standard" for talking about gearing. That's why I gave you the rather long winded explanation before. Try to catch from context what people mean when they say high/low about gearing.

Yes about motor winds/turns. That's straightforward (lower turn/wind is numerically small, high turn/wind is numerically high).
__________________
Team Greasy Weasel

The best upgrade to any car is some driver skill.

Last edited by niznai; 08-05-2009 at 08:24 PM.
niznai is offline   Reply With Quote
Old 08-06-2009, 12:26 AM   #11
Tech Adept
 
ep10's Avatar
 
Join Date: Feb 2008
Posts: 199
Trader Rating: 13 (100%+)
Default

Cool! And thanks....

I gotta study more and experience on it... I guess!
ep10 is offline   Reply With Quote
Reply

Similar Threads
Thread Thread Starter Forum Replies Last Post
Tamiya TA05 Touring Sedan kentech Electric On-Road 11403 06-21-2017 04:10 AM
Electric 1/8th Scale conversion kits. DJ1978 Electric Off-Road 19923 06-12-2017 06:16 AM
Team Associated TC5 RCknight Electric On-Road 13254 05-12-2017 08:58 AM
Electric Touring / On-Road RC Screaming Wind Manila Racers 32167 05-02-2017 11:20 PM
eXpress Motorsports Jon Williams Team and Company Discussions 18296 11-16-2016 03:17 PM
Ask Todd Hodge..aka "Hodgimoto" Todd Hodge Electric On-Road 1957 04-27-2007 08:40 AM



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 06:46 AM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net