We currently do not have a design in the works, but we did prototype one over the summer of 2002.
Our CVT was very basic and consisted of a big round aluminum disc mounted to the side of Skyway's bead lock wheels(
http://www.skywaywheels.com/products_002.htm), an aluminum frame, drill motors/transmissions, and the best part gum rubber.
We mounted the two wheels and discs to the center of the frame, mounted high traction wheels (gum rubber) to the output of the drill transmissions, and then mounted the drill transmission to a moveable assembly that would allow us to move them farther towards the center of the axis of the wheel for more speed or father away for less speed.
The problem was we did not have enough traction to keep the wheels from spinning on the aluminum discs.
This simple cvt prototype/idea was a basically taken from the little CVT's in push lawn mowers.
I don't have a picture of it, I don't even know if we took any of it... so I have included a Paint drawing of what it looked like.
For those of you who know us by our gum rubber wheels (2003) robot and our gum rubber omni wheels (2005) this little project is where found out all about different kinds of rubber and what worked the best, thus GUM RUBBER!