pic: CVT drivetrain

[mechanicalbrain]

loading photo ...

[Conor Ryan]

yeah, Contiunously Variable Transmissions are great. You may want to check this white paper out, from the great team of 217. Do keep in mind its patent pending. I believe they were one of the first teams to try out a CVT, and they were very succesful with it, it's great to be able to have full horsepower at any speed.

Also, CVT's are starting to be used in cars too. The 2005 Ford Freestyle is running with a CVT transmission, pretty cool.

[mechanicalbrain]

all right i came across this in How Stuff Works. the cool thing is that there are no specific ratio it changes how you want it to. its powered by a main motor and then the two servos (A and B) change the position of the two adjustable gears changing from a high to low ratio. note my arrows are slightly off so here's another pic

heres a link that explains more (http://auto.howstuffworks.com/cvt.htm) this type of transmission is more efficient than your standard gear change transmission. it even was in a couple cars for some time but just never got the publicity needed to make it in most cars. it has a smooth shift and you can have any gear ratio you want.

[ahecht]

Originally Posted by cdr1122334455

yeah, Contiunously Variable Transmissions are great. You may want to check this white paper out, from the great team of 217. Do keep in mind its patent pending. I believe they were one of the first teams to try out a CVT, and they were very succesful with it, it's great to be able to have full horsepower at any speed.

Also, CVT's are starting to be used in cars too. The 2005 Ford Freestyle is running with a CVT transmission, pretty cool.

While the CCT was a very innovative transmission, it was not a CVT (if I remember correctly, the CCT was actually a single speed transmission for blending two motors).

Torroidal CVTs, such as the one in your pictures, were used by 190 in 2002 (and our 2003 bot was designed to use a 2nd Generation CVT, but we ran out of time). I know that plans were made available to the FIRST community at the time, but I don't know if a formal whitepaper was ever produced. I'll try to find out.

There are many other types of CVTs out there that would probably be easier to build (the toroidal transmission requires several parts that need to be done by CNC). The Freestyle that you mentioned, like most cars with CVTs, uses a chain that runs in between two sets of two conical pullies. I don't think anyone has tried this type of transmission on a FIRST robot.

[Cory]

The big problem with CVT's made for FIRST is that they're horribly inefficient, and fairly complex.

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.

[ahecht]

^It's all about bragging rights, awards, and pushing the envelope, not necessarily winning or practicality.

[Madison]

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

[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

[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.

[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.

[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.