Final Drive Ratio: Stock R1

[nathanotis]

Talking to the folks @ Holmes Hobbies for their motor recommendations and they posed this question.

I've been searching around, but I can't find it listed anywhere.

[QuesoDelDiablo]

Hm, that's a good question. I've never seen it referenced, you might actually have to work through the manual and find it the old fashioned way..

For reference, the "Old fashioned way" I'm referring to is math. Look at each gear pair starting from the spur and do: output/input=X; that X then becomes your next input and repeat that pattern till you get to the diff.

[nathanotis]

Math, my old nemesis.

[QuesoDelDiablo]

Originally Posted by nathanotis

Math, my old nemesis.

Lol, as is the way...

[nathanotis]

I found a gear ratio chart in the manual showing a stock 12t pinion with a 40.24 ratio. That can't be the final. 12t pinion with 37t spur is 3.08 I'm thinking that's probably not it, either. Got gear tooth counts from the manual. Follow me here...

Three gears in the transmission. The first gear the pinion runs against is 39t, so....

37/15 = 2.6
2.6/35 = .074 (This can't be correct. Continuing this way, the number will be impossibly small. I'm obviously not understanding/screwing up somewhere.) Starting over...

Beginning at the first gear in the trans (Spur?) the gears are as follows:
39/15
35/15
37

Then the diff:
17t
32t

Then the portals
14t
16t

[nathanotis]

Right or wrong, here's what I've done/come up with:

Trans ratio:5.71
Diff Ratio:2.71

So then you add those together for a total (8.42), or divide them (2.107) and use that as the input to the portals (3.165) for a portal output of 1.5?

I'm lost. And my brain hurts.

[nathanotis]

Thinking about the transmission... I'm making it too difficult. the 15/35/15 nonsense in the middle can be disregarded since it functions as a pass-through between the 39 and 37, but cancels itself out (right?).

39/15
35/15
37

So...
Trans out/in 37/39 0.9487179487
Diff out/in 32/17 1.882352941
Portal out/in 16/14 1.142857143
Final drive - 3.974

Can anyone verify this is correct?

[QuesoDelDiablo]

sorry that I don't have time to dig in and find it but I think there's a mistake somewhere, Axial FDR's are somewhere around 50ish so I'd expect the R1 to be somewhere in that range, or at least between 25-75..

[nathanotis]

Originally Posted by QuesoDelDiablo

... Axial FDR's are somewhere around 50ish ...

I went to check out the Capra manual, but the tooth count isn't listed for any of the gears save for the portals (23/12). All the trans and diff gears are listed in kits with no description.

I'm done chasing this for a while. If/When the time comes, I'll either figure it out or just buy a nice slow crawler motor and call it good.

EDIT: Who am I kidding? I can't leave a puzzle unsolved. I found another thread that I hope will help. I'll post back with my findings.

[swervo]

Place a mark on the spur and a pointer on a wheel hub . Rotate the spur until the wheel hub has done a complete rotation . Factor in the pinion then for the gear ratio .

[OSRC]

Originally Posted by nathanotis

I found a gear ratio chart in the manual showing a stock 12t pinion with a 40.24 ratio. That can't be the final. 12t pinion with 37t spur is 3.08 I'm thinking that's probably not it, either. Got gear tooth counts from the manual. Follow me here...

Three gears in the transmission. The first gear the pinion runs against is 39t, so....

37/15 = 2.6
2.6/35 = .074 (This can't be correct. Continuing this way, the number will be impossibly small. I'm obviously not understanding/screwing up somewhere.) Starting over...

Beginning at the first gear in the trans (Spur?) the gears are as follows:
39/15
35/15
37

Then the diff:
17t
32t

Then the portals
14t
16t

Portals = (16/14) = 1.14
Axle = (32/17) = 1.88
Trans assuming a 12t pinion = (39/12)*(35/15)*(37/15) = 18.68

1.14*1.88*18.68 = 40.2 FDR

Page 18 on the kit manual shows the FDR for pinions 9 (53.65) through 19 (25.42) ... yes, it is correct.