Proper Gearing in relation to motor turns?

[Dazzler]

First off, I am aware of how changing spur and/or pinion gears changes primary drive ratio, and therefore Final Drive Ratio. I do know that a 5:1 ratio will give more topspeed but less torque than say a 7:1 ratio

I'm just confused on how it all relates to different motor.

Is far as I know, a motor with lots of turns (ie: a 27T stock) will have a lower RPM but a higher torque than a motor with less turn (ie: a 17T), which will have higher RPM's, but less torque

Hope I'm correct so far.

I understand that, given a motor has less torque, it must be geared lower (right? I'm always confusing higher vs lower geared) in order to have enough power to move the car. Lower gear however means less top speed, but the increase in RPM of the motor will make up for that.

But if a 27T motor with lots of torque can be geared higher, this in return would compensate for the lack of RPMs.

For example:
(numbers taken from the website of a mfg of RC motors)

Number of Turns/RPM/Recommended FDR

17T / 29200 / 6:1
15T / 34800 / 7:1
13T / 35600 / 8:1
12T / 41100 / 8,5:1
11T / 44300 / 9,5:1

Doing the math, the RPM of the wheels would be (theoretically):

17T: 4866 RPM
15T: 4971 RPM
13T: 4450 RPM
12T: 4835 RPM
11T: 4663 RPM

So, looking at the numbers here, a 15T motor would give me the highest speed, and a 13T would give me the lowest speed. I wouldn't even opt for the 11T, since it would give me the lowest speed (by one)

This is so confusing to me, because all you ever hear is you should use a 11T or 6T or 8T or whatever low number of turn if you want a fast car. But these motors have lower torque, and by compensating for that by altering the gearing, you *actually* end up driving at lower speeds!!

Maybe I'm missing something here, but I just can't seem to figure out how this gearing ratio and motor rpm/torque inter-relation works....

[2ndGeneration]

Hello Dazzler,
Welcome to the boards.
With that said, there has been a huge amount of time and bandwidth devoted to this very topic.
Use the search option and do a search for "gearing" sift through the results for the information that pertains to the answers you seek. Here (http://forums.radiocontrolzone.com/showthread.php?t=200011&highlight=gearing) is a thread as well as this (http://forums.radiocontrolzone.com/showthread.php?t=201532&highlight=gearing) followup thread, and another (http://forums.radiocontrolzone.com/showthread.php?t=201732&highlight=gearing) .
Good luck, hope this helps. :D

Also just found this (http://forums.radiocontrolzone.com/showthread.php?t=200599) very informative thread.

[Dazzler]

Hey,

I've read all them links previously before posting, I understand there's a search-function for this ;) Thanks anyway

Anyway, those topic were all about what gearing actually is/does, were my question is more towards how it relates to to motor itself. Look at my example. That's what I'm curious about, why should I buy myself that 11T motor, when I would have far better performance (looking at the numbes that is) with that 15T motor!



Hello Dazzler,
Welcome to the boards.
With that said, there has been a huge amount of time and bandwidth devoted to this very topic.
Use the search option and do a search for "gearing" sift through the results for the information that pertains to the answers you seek. Here (http://forums.radiocontrolzone.com/showthread.php?t=200011&highlight=gearing) is a thread as well as this (http://forums.radiocontrolzone.com/showthread.php?t=201532&highlight=gearing) followup thread, and another (http://forums.radiocontrolzone.com/showthread.php?t=201732&highlight=gearing) .
Good luck, hope this helps. :D

Also just found this (http://forums.radiocontrolzone.com/showthread.php?t=200599) very informative thread.

[Hachi_Roku]

Well theoretically maybe a 15 turn would be faster than a 11 turn. But actually when you install it into the car and gear the motor so that it is appropriate to your needs (track size etc) the 11 turn is faster. Usually the lower the winds, that faster the car (and thats from personal experiece).

[gizmoguy303]

Your calculations are based on the general idea that the lower number of turns, the lower the torque and higher the RPM. That is not quite the case. Simply put, lower turns = more overall power (watts). The power gain, from going from a higher turn motor to a lower turn motor, is comprised of both RPM and torque to a point, then after that point it becomes increasingly RPMish. If you look at a gearing chart for a specific vehicle you can see where, starting at a 27 turn and going down, the pinion recommendations will rise to a point, and then fall almost linearly.

The EASY way to figure it: lower turns = more power. Start your gearing at the recommendations in the manual and experiment from there. Usually a 10-14 turn is used in buggy, 10-12 in truck, and down to 6 or 7 turns in sedans.

[cheerwhiner]

check out www.gearchart.com

[cmdj_chris]

As a self proclaimed gearing guru, I have a few thoughts. Gizmo is on the right track. The lower turn, aka modified, motors have more power output. Before talking about gearing, are you planning on racing in a structured class system, or just getting together with friend in an empty lot? Most structured or sanctioned events have class restrictions dealing with motors, batteries and bodies.

To address the question of this thread.....

Every motor whether stock or mod, will turn a certain rpm at a certain torque rating. Torque is measured by the amount of power the motor has. take a 27 turn motor that turns 29,000 rpm and a 10 turn that turns the same rpm. Believe it or not, I have seen a stock motor and a mod motor turn rpm's that were very close (less than 100 rpm difference). The 10t has less rotational mass than the 27t which means it takes less power to get the motor spooled up. So if both motors have the same torque rating, the 10t will be twice as fast because the bottom line is this:

SPEED IS AFFECTED BY HOW FAST THE MOTOR REACHES IT'S MAX RPM

There is no magic ratio for each motor. You could take 2 P2K2 27t stock motors and the will have different torque and rpm values. There are different racing environments. Are you running on road or off? What batteries are you running? How many cells? If you are racing competitively, read my post on gearing guidlines here (http://forums.radiocontrolzone.com/showthread.php?t=200011)

If you are just bashing around, start with a lower ratio. It will give you more runtime from your batteries and will extend the life of your motor.

[adam lancia]

i thought about this same question for quite a while too. i read an article in cycle world that kind of clarified it for me and i'll see if i can regurgitate that info correctly (firts time i've used regurgitate in a sentence i think...). with increasing rpm, torque generally decreases. however, if the increase in rpm is greater then the decrease in torque, more power will be made because the engine/motor is spinning faster, making a little less power per revolution but spinning at a speed that it makes more power in a given time frame therefore making more overall power at higher rpm's. there's a formula to figure out horsepower, i think it's torque x rpm x some number. i don't have the article anymore but if someone can support this or correct it, i would appreciate it.

adam