I need a gear calculator

[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?

[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