ep10

iTrader: (13)

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!

sosidge

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).

niznai

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?

ep10

iTrader: (13)

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

iTrader: (13)

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

iTrader: (13)

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.


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.

sosidge

Corrected.

sosidge

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.

ep10

iTrader: (13)

In term of acceleration, same motor with low ratio (9:1) will be better than high ration (6:1)???

niznai

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).

ep10

iTrader: (13)

Cool! And thanks....

I gotta study more and experience on it... I guess!