pic: CVT drivetrain

[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.

[mechanicalbrain]

by the way id love to AIM you but im having trouble with CDs set up if anyone could tell me what to do.

[jgannon]

Originally Posted by M. Krass

What is it about inefficient design and operation that either pushes the envelope or deserves to be awarded?

If it wasn't for all of the green bars by your name, I'd have disregarded this post as a troll. Rather, what we have here is a logical fallacy known as "begging the question"-- the premises for your claim entail your conclusion. What is the relative efficiency of a miniature CVT, compared to an Andymark transmission, or a 33 transmission? It's hard to say, because nobody has tried it.

A genuine CVT on a FIRST robot would be an innovation. Maybe it will turn out that the team who does it (next year, maybe?) would have been better off with an Andymark shifter. Obviously, then, the team shouldn't get an award. What a total waste of time.

NO!

While the CVT team is out getting pushed around, they say, "Hm. That didn't work as expected. How can we improve this design?" THAT'S what FIRST is about. I'd say that's worthy of an award. Or, on the other hand, maybe the CVT is reasonably efficient. Then we all have a new design to consider. I'd say that's worthy of an award.

Keep this in mind:

Originally Posted by mechanicalbrain

a CVT is hardly ineficient all it means is nobody has created an efficient one

How inefficient will the first FIRST CVT be? We don't know. In response to your question, inefficiency neither pushes the envelope, nor deserves to be rewarded. New approaches and inspiration do both. That's why I'm confident that whoever gets the first CVT on the playing field will gain acclaim here and with the judges, regardless of its efficiency.

</soapbox>

[Cory]

Originally Posted by jgannon

That's why I'm confident that whoever gets the first CVT on the playing field will gain acclaim here and with the judges, regardless of its efficiency.

Well... 190 made a toroidal CVT in 2002.

I think Maddie's point was that there's no sense in making (or being rewarded for) something that will perform poorly, because it is cool, instead of making something more traditional that will perform better

[ahecht]

Originally Posted by jgannon

A genuine CVT on a FIRST robot would be an innovation. Maybe it will turn out that the team who does it (next year, maybe?) would have been better off with an Andymark shifter. Obviously, then, the team shouldn't get an award. What a total waste of time.

Keep this in mind:How inefficient will the first FIRST CVT be? We don't know. In response to your question, inefficiency neither pushes the envelope, nor deserves to be rewarded. New approaches and inspiration do both. That's why I'm confident that whoever gets the first CVT on the playing field will gain acclaim here and with the judges, regardless of its efficiency.

I will point out again here that 190 did use a true CVT (of the torroidal design shown here) on their 2002 robot. While I don't know the efficiency of the system, I can say that we never experienced any slippage (and all the rubbing parts were smooth cast iron, not rubber or wierd hybrid gear thingies). The rotation of the two idlers was controlled by a single motor, since they do not need to move independantly of each other.

Yes, the system was very noisy, and we didn't get the programming figured out until well into the 2003 season (you try programming a reliable PID controller in pBasic), but it did show promise, and I would hope that more teams would try ambitious projects such as this. It may take several generations before a radical design such as a CVT can show a clear competative advantage, but we will never find out if teams aren't willing to try.

[jgannon]

Originally Posted by Cory

there's no sense in making (or being rewarded for) something that will perform poorly, because it is cool, instead of making something more traditional that will perform better

I'll concede that point. There's no sense in, say, making a drivetrain powered by one Globe motor. Would it be unique? Yes. Would it be cool? Sure. Would it perform well? It's safe to say no. However, I don't think it's fair to assert now that a CVT will perform poorly, particularly when only one design has been tested.

[alphastryk]

here is a non-friction-based CVT:

http://www.andersoncvt.com/device.wmv

i dont know if it is feasable to make this type of CVT, and you would have to ask this guy, because he has a patent on it, so...

[sanddrag]

Originally Posted by alphastryk

here is a non-friction-based CVT:

http://www.andersoncvt.com/device.wmv

i dont know if it is feasable to make this type of CVT, and you would have to ask this guy, because he has a patent on it, so...

I've seen that before. To me, that still does not look like a positive engagement system.