CVT a bike engine

[Yoshi]

I had the cvt idea off the clutch basket about 3 years ago, never got around to doing any real prototyping though.  I did get a basket from my buddy at the time to see what would be involved, and I determined it would be pretty simply.  Basically, break the rivets loose that hold the basket to the primary gear, make a steel plate that will attach to the primary gear with an output shaft.  Make a new center plate for the clutch cover that is thicker and contains a bearing and a seal, turn the motor around backward and your good to go.  I was gonna run an axle out to each arm and running a chain down each trailing arm to the wheels, basically as much travel as you want, only limited by the shocks. Here's a couple pics of the basket I have here, the crank spins the outter gear..

Problem your gonna have running off the basket, or 6th. gear, is your gonna need around a 12.5:1 gear ratio for the low gear, and a 5:1 gear ratio for the high gear, I don't know any cvt's that can handle that..

[Nutz4sand]

http://detroit.craigslist.org/for/950538436.html

By the time you sell the motor you got and part out the rest of this sled on evil bay you will not have a too much into it for this motah.  Putting it in would be a no sweat compared to some things.....

[Yoshi]

here's a shot of the tranny (taken by a member in the edge forum), the clutch input shaft is on the left of the pic, you can see the crank gear just to the top left of the screen...

[Engineer]

[Engineer]

The problem with not using the solid shaft is that the clutch basket rides on a bushing that rides on the tranny input shaft.  This bushing is slipping any time the clutch is pulled in.  When the clutch is out, the bushing is just setting on the shaft.  This arrangement is not going to like any side loading out past the clutch cover.  you might get away with making a solid piece that has the splines of the clutch plates on the inside, and the ears of the clutch disks on the outside, to just make the clutch solid.

[Yoshi]

How do you think that his CVT accomplishes this now?

judging by the size of all the cvt's i've ever seen, I don't think any off them are producing 12.5:1 ratio's for low gear.

[Engineer]

judging by the size of all the cvt's i've ever seen, I don't think any off them are producing 12.5:1 ratio's for low gear.

Exactly, that is why Bug is having a low end problem.  The clutch tries to mask the problem of not having a low enough gear.  But you can't gear it any lower, because a CVT only has so much "shifting" potential, and you would limit the top end.  That is why a bike that wants to go from 0-190 has six gears.

[Boostinjdm]

I am just trying to figure out if you guys are confused or I am.  a cvt with 3:1 gear ratio in low and a 5:1 reduction in the gear box.  Gives you a 15:1 reduction from the drive clutch to the axle.  If your cvt setup had a 12:1 reduction and a 5:1 tranny behind it that would be 60:1 between the drive clutch and the axle.  If you had 28" tall tires and could put that power to the ground, your 0-11mph times would be incredible, but it would prolly take you all day to get very far.

[Yoshi]

I am just trying to figure out if you guys are confused or I am.  a cvt with 3:1 gear ratio in low and a 5:1 reduction in the gear box.  Gives you a 15:1 reduction from the drive clutch to the axle.  If your cvt setup had a 12:1 reduction and a 5:1 tranny behind it that would be 60:1 between the drive clutch and the axle.  If you had 28" tall tires and could put that power to the ground, your 0-11mph times would be incredible, but it would prolly take you all day to get very far.

In my calculations, there was no 5:1 gearbox behind it, the 12:1 ratio achieved by the cvt is assuming the back of the cvt is the final drive ratio with the axles coming out of it, I guess I never really though about putting another reduction behind the cvt, which is what everyone does so I guess I should have......

factoring in the 5:1 ratio after the cvt, I believe you only need a 2.5:1 reduction for the low gear, and a 1:1 for the high gear.....if I did the numbers correct..

problem is the input for the cvt won't even break 6900 RPM.  You need a  little higher crank/primary gear ratio for the cvt to get where you want, which a possibility, if you could fit it, would be to stick a custom gear on the crank that was a little bigger, and a little smaller gear for the clutch basket....

[Engineer]

I am just trying to figure out if you guys are confused or I am.  a cvt with 3:1 gear ratio in low and a 5:1 reduction in the gear box.  Gives you a 15:1 reduction from the drive clutch to the axle.  If your cvt setup had a 12:1 reduction and a 5:1 tranny behind it that would be 60:1 between the drive clutch and the axle.  If you had 28" tall tires and could put that power to the ground, your 0-11mph times would be incredible, but it would prolly take you all day to get very far.

LOL.....  That is some good stuff right there!  and true!

[Boostinjdm]

just for clarification.

An engine is an engine.
A cvt is a drive, a driven, and a belt.
A tranny, gear box, chain case,  is a way to further change rpms and torque.

In a buggy that contains a cvt, you have to have all three.

Primary reduction is the first change in rpm from the crank.
in this case it would be from the crank to the clutch basket. 

[SPEC]

This is sorta off topic and on topic, I know Bug's woes well, going to a smaller tire would help alot... With the CVT's I work with as I stated in sled power is 3.38 to 1 at 1st engagement...If I remember right Bug's box is like 4 to 1? this is only giving a 7.38 out of the hole and reducing as the CVT does it's job...

[Admin]

a cvt generally is driven directly from the crank, so they see from 0-8500 rpms range of use, I could see possibly tuning from the basket, but i cant see tuneability from the countershaft, you guys are confusing yourself is all...

[fabr]

Why can't a cvt be tuned for 6500 max I don't see the problem .Educate me.

[Engineer]

I think because it works on centrifigual force.  The greater the range, the greater the tunability.  I think it is exponential to..... as the rpm increases.

But I would think that all of the change would be in by 6500?