A few thoughts:
If you're planning on using some sort of flat timing belt, it appears that there will be significant twisting occuring, since the cones are pointed in opposite directions. The belt could have a difficult time fitting around either cone edge. You may end up with only an edge of contact, which could reduce the life span of your timing belt significantly.
A few "deep" thoughts... and some questions that you may want to ask yourself:
Why do you want to build this? Is this for a hobby or for a competitive advantage? If this is for competition, what advantages does this sort of design carry over dual speed, on-the-fly shifting transmissions?
Benchmarks to compare:
- Complexity / Ease of Manufacturing
- Ease of Repair
- Weight
- Reliability / Consistancy
- Performance
Before you get too far into this design... these are some questions you may wish to ask yourself. Initially... I think that you're mostly looking to improve performance, since you'll have a "perfect" gear ratio every time.
Do you really need a "perfect" gear ratio?
Some other things to think about_:
CVTs are often used in motors that are running in one direction for (reasonably) long periods of time with moderate changes in torque needs. How does this design handle start and stop (and reverse motion!) that are so common in FIRST competitions?
Just some questions to ask yourself... good luck!
Matt