Adding an "idler" gear for reverse rotation?

[sbcnyc]

I was wondering if adding an idler to my spur gear, than driving the idler off the pinion changes the overall ratio of the transmission.. I've heard of this being done, but nobody ever got in to the dynamics of the ratio, like does the idler now act like a pinion gear?

[GoMachV]

As long as the idler is not a compound gear (like you see on an Ultima or the early Traxxas cars) then it won't effect ratio. For example, the idler gear inside the trans is not figured into the ratio between the top shaft and diff gears.

I did this bitd with an Eagle that I converted to nitro well before the Nitro Hawk came out.

[sbcnyc]

Cool, so do I have to match the tooth count on the internal idler gear?

[jwscab]

Nope. Just find a gear that fills the gap and you are good.

[klavy69]

I did this bitd with an Eagle that I converted to nitro well before the Nitro Hawk came out.

Closet Traxxas guy... You and scr8p being the closet Kyosho guy should start your own club.

[GoMachV]

I'm ok with traxxas, as long as it came with white plastics

[sbcnyc]

So my big question is how do you now calculate your final drive with the additional idler, does it affect the pinion/spur/final drive ratio?

i worked out mounting a gear in between, but clueless how it affects pinion spur selection or where to read up on basic gear calculation...now that i got my sensored stuff running in the correct direction, id just go out, run, and temp the motor but id like to know the actual calculation or theory required. if there's an effect on final drive

[jwscab]

It doesn't. just use the pinion/spur math times the internal ratio. the idler is 1:1 between the pinion and spur, it doesn't work into the calculation.

[sbcnyc]

Done and done. Thanks all!