How to determine gear ratio?

[Trikster]

Stupid question, how (what is the math) does one determine a final drive ratio? I know the math for a spur/pinion, but how do you work out the rest of the tranny? For example, how does one go through a Pede tranny to determine its final ratio?

 

[Mechanicalbob]

To get the final ratio of your tranny is easy well sorta mark the output shaft of the tranny and count how many times it goes around for the input. The tranny ratio of an electric Pede is 2.72:1 So if you have a input of P/S of lets say 4.75:1, you would multiply 4.75 by 2.72 and your tranny out put is 12.92:1. If your axle has a ratio of 2.86:1(Maxx diff ratio) multiply it by your tranny output 12.92:1 and your your final ratio is 36.95:1 at the wheels. Now to find out torque of your truck. If you know the torque output of your motor/engine. If I remember right Multiply your torque with the tranny output, then your diff ratio and then devide by the numer of wheels being used and you have torque at the wheels. So lets say you have 5 LBS of torque, your tranny output is 12.92, multiply them and get 64.6 now multiply that by your diff ratio of 2.86 = 184.76 then devide by 4 (number of wheels being used) = 46.19 LBS of torque at each wheel. Hope this answers your question.

Steve

 

[Mechanicalbob]

Here is some other information that might be helpful to some. The electric Pede and Rustler share the same gear ratio of 2.72:1, not taking into accout the input gearing. The electric Pede does have some bigger gears but not by much. The nitro Pede has a tranny ratio of 3.75:1 and the nitro Rustler has a ratio of 2.81:1 without input gearing. The nitro Pede has tougher gears than the Rustler. So if you can mount a nitro Pede tranny in your crawler you could get a lower ratio. If you have an input of 4.75, tranny at 3.75 axle at 2.4:1 (tlt I do beleive) your final ratio at the wheels would be 42.75:1

Steve

 

[Fishmaxx]

Good Stuff"thumbsup"

 

[Trikster]

So let me make sure I understand...

Divide the output gear (spur) by the input gear (pinion) to get your ratio. If you have another set of gears, you multiply the resulting ratio of the next set of gears with the first set of gears?

Am I correct? Reason I ask is that I am wanting to make a custom tranny for my TLT scaler. A Pede tranny is just too tall even laying down and cut down.

 

[Mechanicalbob]

So let me make sure I understand...

Divide the output gear (spur) by the input gear (pinion) to get your ratio. If you have another set of gears, you multiply the resulting ratio of the next set of gears with the first set of gears? Am I correct?

Reason I ask is that I am wanting to make a custom tranny for my TLT scaler. A Pede tranny is just too tall even laying down and cut down.

Yes you are correct. Just remember most of the time it is the bigger gear devided by the little gear to get your ratio. Now for a custom tranny there are several ways to make one. It all dependns on the type of gears you want to use and your target final ratio.


One idea is to use a Tamiya TL01 gear box If I remember right it has a ratio in the range of 4.45:1. You will have to do a bit of cutting to get it down to size but I do believe it will be smaller than a pede tranny. Also you could use the center shaft for a trailer axle. The ends are pined all you would have to to is thread the ends and you are good to go.

If you have any questions feel free to ask or PM me

Steve

 

[Trikster]

Thanks for all the input. I am glad I asked, I was adding all the ratios together instead of multiplying and could not figure out why I never got the same results as anyone else.