CVT Transmissions

Has any team ever tried using a continuously variable transmission on their robot?

yup, a couple teams have made them.

190 in 2002.
494 made one, iirc.

I’m forgetting a few others too.

To help Cory out. 217 did a version too they call it a cct it’s not exactly a cvt but close, information on 217’s cct can be found in the chiefdelphi white papers.

Yeah, it was a team member’s senior project. It was a lot of fun and pretty cool to see on a robot, but it was very heavy (had a lot of cast iron for wear) and not entirely necessary.

If you’re looking for a fun challenge and some style points, I recommend giving it a try.

494 built their CVT in 2005, I remember seeing their demo transmission in Atlanta.

It is also at their website at Thunderchickens.org

84 had their “Infinity Drive”](http://www.chiefdelphi.com/forums/showthread.php?t=56911) last year.

They had it at IRI 2004 too, so they must have built it before 2005 :rolleyes:
I don’t believe they ever used it on a robot though.

There is an excellent book out there called “Traction Drives: Selection and Application” 1/2 the book is gear-less fixed ratio systems, and 1/2 are CVT or IV T systems. These designs typically have pitfalls above 10 hp and start requiring exotic designs, traction fluids, and controls. CVTs have really started to make a comeback in the automotive sector, but we are also learning about some of their disadvantages too. I am a huge fan of CVTs, but I also understand that for many applications they are not terribly practicle. This is a great off season project, but would probably hinder development during the actual build season.

Thanks for the tip! I just went and picked it up from the UofA library, looks like a great read with way more info than I ever needed. Maybe if we find a clever way to implement one, it will appear on our robot next year… doubtful though.

That book will leave out the most common CVT which is the rubber belt with expandable sheaves. This type is used on many snowmobiles, mini-bikes, and SAE Mini-Baja cars. This style CVT s really cool because it has passive controls that basically shift it into a lower “gear” as there is a higher torque request. This is accomplished by a cam style spring loaded clamping mechanism on the sheaves (pulleys).

Best of luck. Also, There is a really interesting way of running a CVT with a differential like arrangement in such a manner as to create a geared or locked neutral.

With the vex differential gears and 2 motors, you can have one motor drive the outer gear and another driving one of the left or right axles.

The only thing I’m wondering is, unlike those CVT (e.g. the belt drive one), at lower speeds is basically one motor reducing the rpm of the output shaft since the primary motor is always spinning at full speed. Does this really create more torque?