I need a gear calculator

[Modding_out]

Hey, I need some help finding a gear calculator. I have searched for a long time but I haven't been able to find what I'm looking for. Every single gear calculator I found is used for calculating Roll out and top speed. I need one that's going to tell me: ''gear A. + gear B. = gear ratio of X.'' I haven't been able to find it, and I was wonder if you guys could help me. thanks.

[BrianG]

Well, that's probably because gear ratio is simply the result of dividing two gear tooth counts. So, for a 90T spur and 20T pinion, the ratio is 4.5:1.

[Modding_out]

Really? It's that simple? could you give me the formula to I can do it my self? Thanks.

[BrianG]

Yup, that simple.

ratio = output_gear_tooth_count / input_gear_tooth_count.

[Modding_out]

Originally Posted by BrianG

Yup, that simple.

ratio = output_gear_tooth_count / input_gear_tooth_count.

Thanks! I did it and got good results but what is this*?
4.5:1 <= * the :1?

Edit: I figured out what it means, :1 = 1 full rotation. So 4.5:1 means it the motor 4.5 rotations to turn the tires once.

[BrianG]

Yup!

[Modding_out]

Hey, Brian. I have another question, how do you find the gear ratio of 3 gears? Because 3 seems to be a common number found in most trannys. (omitting two speeds)

[MetalMan]

I'm not Brian, but...

That middle gear is typically referred to as the "idler" gear. It's named that way because it doesn't affect the overall gear ratio, it merely reverses the direction of the output and puts distance between the input and output gears. For example, the Rustler transmission has a 22t top gear, 30t idler, and a 60t differential gear. The overall ratio is about 2.72:1, and if you calculate out the ratios:
22/30 = 1:1.36
30/60 = 1:2
Multiply those two ratios together, and you get 1:2.72 (the same as 2.72:1, I just flipped the numbers in this case).

The same can be accomplished by the first and third gears:
22/60 = 1:2.72

[Modding_out]

Originally Posted by MetalMan

I'm not Brian, but...

That middle gear is typically referred to as the "idler" gear. It's named that way because it doesn't affect the overall gear ratio, it merely reverses the direction of the output and puts distance between the input and output gears. For example, the Rustler transmission has a 22t top gear, 30t idler, and a 60t differential gear. The overall ratio is about 2.72:1, and if you calculate out the ratios:
22/30 = 1:1.36
30/60 = 1:2
Multiply those two ratios together, and you get 1:2.72 (the same as 2.72:1, I just flipped the numbers in this case).

The same can be accomplished by the first and third gears:
22/60 = 1:2.72

Hmm. so your telling that no mater what the size the idler gear is, it doesn't affect the gear ratio? How does that work?

[bl-is-future]

you don't do three at once. You get the gear ratio of 1st gear then the ratio of 2nd then the ratio of 3rd and so on.

[Modding_out]

OK.....could some one tell me the number of teeth a Emaxx tranny has is second gear. The specs on the 3905 emaxx say it has a overall gear ratio of 18.6 something, but I don't know if that includes the diffs or not.

[BrianG]

Originally Posted by Modding_out

Hmm. so your telling that no mater what the size the idler gear is, it doesn't affect the gear ratio? How does that work?

Think about it, there's no reduction at all. Like MM said, it's just to add a little extra distance between the shafts and/or reverse the direction. When an idler gear is present in this way, you could just divide the output by the input and disregard the idler. But, to keep things consistent, you could figure in all the gears. Consider a tranny with an input of 20T, idler of 10T, and an output of 40T:

Disregard the idler: 40T/20T = 2
Figuring in the idler: 40T/10T X 10T/20T = 4 X .5 = 2

See? Same thing!

However, if you add an extra gear to the idler area, things change. Basically, you'd have the input gear meshing to an idler gear. But if you have a smaller (or larger gear) that is on that same idler shaft meshing with the output gear, the ratio then is Ouput/Idler1 X Idler2/Input.

My page has many transmissions listed and shows the various tooth counts whether the tranny has 2, 3, or 4 gears: http://scriptasylum.com/rc_speed/_data.html

[Modding_out]

ok, now it makes sense, but I have another question. does tooth pitch have any affect on gear ratio? because the calculator doesn't care if the pitch is 48, 32, or mod.1 a 18t pinion is an 18t pinion

[BrianG]

Nope, pitch doesn't care. It's all about the ratio of the gear diameters. And since the gear diameter is directly proportional to the number of teeth, it's easy to use tooth counts instead. You could measure the gears and divide the diameters or circumference and get the same result.

[Arct1k]

Quick proof:

Gears a, b & c


(a/b) * (b/c) = (a* b)/ (b * c) = (a / c) * (b / b) = (a / c) * 1 = a / c

IIRC on Mod 1 = Diameter in mm is number of teeth + 2mm