pic: CVT drivetrain

[sanddrag]

Originally Posted by Cory

I'm not sure you'd even have a reason to make one, rather than just making a auto shifting 4 speed like 33 did, other than for the coolness factor.

I was talking with a team from Hawaii (368?) that made an autoshifting team 33 style 4 speed and they said as soon as it hit 2nd it went right to 3rd almost immediately after. So even 4 speeds is excessive for a traditional FIRST game.

[mechanicalbrain]

actually a CVT is hardly ineficient all it means is nobody has created an efficient one. i once saw a race car with one... VERY COOL the car lost absolutly no RPM when shifting gears and you didnt have to wory about "shocking" your transmission when performing high speed gear shifts. the main benifit with this pertaining to FIRST is you can actually make them VERY simple (although with a few costom done parts) and you have a more complete control over a direct drive torque to speed ratio. i also looked at torque converters but they were too much of a hasle.

[techtiger1]

Originally Posted by mechanicalbrain

actually a CVT is hardly ineficient all it means is nobody has created an efficient one. i once saw a race car with one... VERY COOL the car lost absolutly no RPM when shifting gears and you didnt have to wory about "shocking" your transmission when performing high speed gear shifts. the main benifit with this pertaining to FIRST is you can actually make them VERY simple (although with a few costom done parts) and you have a more complete control over a direct drive torque to speed ratio. i also looked at torque converters but they were too much of a hasle.

So someones read the hows things work on CV T's . While CV T's can be and are if well made more efficient then regular transmissions in order to make a efficient one many calculations are needed. Refer to Paul's white paper. Keep in mind as well that the design you have shown requires three motors or two servos and a motor if you wanted to use servos for the rotation of the inner disc's a lot to invest in one gearbox at least in my opinion. All I am saying is this is no cakewalk to produce something like this that is efficient.

I was interested so I added my comments after some research,
-Drew
team 1251
Tech tigers

[Gdeaver]

Our team has had good success by following the KISS principle. We would consider a CVT a violation of the KISS principle.

[santosh]

The new Nissna Murano has one and the new Audi A4 have CVT's too. I <3 CVT's. Me and my friends were talking about the very low RPM running where as some engines get most of their power out at higher rpms. We were thinking that they could possibly move the cones on command of the driver so that the driver could control the rpm level.

We would love a CVT. We just want one that isn't entirely friction based, but still they are so awesome. Something that is dependable.

[mechanicalbrain]

basically i would need a company that can make the gear to sponcer us to get these into first (i need four). even if they are given to us and counted as a tax right (i love being a nonprofit org) off it would still need to go into the budget and one of them could take up most of the budget. each gear would have to be cut from a block of aluminum. i have a way I'm sure i can run it off one servo. and what would be the point of giving up i would only be guaranteed failure. i like this design because gears are more reliable than chain. (please no personal stories it my opinion and i in no way claim it as a fact) besides a couple years back if you had said half the things we do now to anyone they would say its impractical or not even possible and yet we manage to get this far on stubbornness (and i say stubbornness because genius can only give man wings not teach him to fly). no smart retorts on that last line!

[mechanicalbrain]

actually i planned to gear it not run it based on friction

[sanddrag]

The problem with gears in CVTs is that with a varying diameter comes either one of two things:

A varying pitch, or
A varying number of teeth

And I don't see how either circumstances could properly mesh with another gear. That's why I've never seen an actual cone shaped gear and that is why most CVTs are friction based.

The only thing I've seen that is close to being a mechanical CVT was the ThunderChickens CCT which used a motor to drive the ring gear of the planetary as well as the sun.

[santosh]

How would that work. I am very curious. I would love to know.
edit: in reference to mechanicalbrain's gearing and not friction

[mechanicalbrain]

well if you gear it (and i admit the gears would need i bit of slop) correctly the sides will still be able to slide though i couldnt use servos without gearing them. actualy the im positive that if you gear all four of the gears (agian with a little slop) they would rotate perfectly and still slide. to test this im making some oversized wood ones. the concept isnt that impossible and i was believe imployed in some cars or at least that is what im told. to clarify the picture is misleading in that in not tapering that much. admitedly theres some math. it also helps to have fine teeth on the movine gears.

[mechanicalbrain]

actually now that i think about it both the moving and not moving parts can have the similar change of gears teeth spacing and as you rotate a different spacing is used because a different area touches. its difficult but entirely possible. the trick is to have the least possible area of contact.

[mechanicalbrain]

or inversely geared teeth would definiteley work but im not sure how it would change the gear ratio.

[santosh]

I know for a fact that the new Nissan Murano uses cones. I am not sure baout other stuff though. Wow you are right. But when you swivel now that I think of it, the entire thing changes. and screws up. I think?

[santosh]

Um, I dont think that would work either. Get on aim an maybe we can discuss this some.

[mechanicalbrain]

allright i could half gear it half use friction or i could go all out and do friction with a material like rubber of course i would have to pick the right type.