pic: 2 Speed V.2

[sanddrag]

Originally Posted by sanddrag

I'm thinking you could drop that 60T gear down to something like a 45T. This would keep your high gear ratio the same but increase your low gear rpm (decreas the ratio) and decrease the ratio between them making for a 3:1 difference.

I'm fairly confident that you could even fit a 40T in between the CIMs if you wanted to as long as you keep the axes of rotation of the CIMs and the 40T gear all in the same plane. (my rough calculation shows you should still be left with about .080 between the CIMs).

This would give you a 2.67:1 difference between high and low which I think is pretty much optimal. This would bring your low speed up to around 4.5-4.8 fps which I think is much more useful.

Have you determined that you must be geared for a low 3fps before you can slip the tires without tripping breakers? I'm thinking you can gear a little higher than that and not trip breakers and still slip the wheels.

Oops, C-C distances totally skipped my mind when posting this. I'll come back with an edit and fix that problem.

EDIT: Okay, some of the things in my above post are largely inaccurate due to you need the same center to center distances for high gear.

BUT, I have gotten it all worked out. I think you should do this.

Keep the 12T gears on the CIMs
Those are both in mesh with a 45T gear
The 45 tooth gear meshes with the existing 30T gear

This concludes the high gear lineup and you now have a 3.75" c-c distance between the shafts provided these are 20DP gears. Now for low gear:

On the same shaft as the 45 tooth gear is 25 tooth gear (replaces the 30T non-dog gear you currently have).
In mesh with the 25T gear is a 50t gear (replacing the 60T dog gear)
and you still have a c-c of 3.75 so everything is in mesh.

And that concludes the gearbox. If it isn't clear, I can draw it.

This will get you a smaller lighter setup with the same high speed and a better (faster) low speed. You will have a 3:1 ratio between high and low.

Another option would be to run a 40T gear initially (instead of the 45T I mentioned above) mating with the 12T gears and instead of the 25T gear mentioned above, drop that to a 20T. This will give you a 3.5" c-c distance and a 3.33:1 ratio between high and low.

Or with the 40T gear initially you can go 25:45 for low which will give you a 2.4:1 difference between high and low.

It is all up to you. But the three options I listed are lighter and smaller than what you currently have. Also a bit cheaper money wise.

In any case, I think 4:1 difference between high and low is too much.