In respect to a CVT transmission, too much cost, weight and complexity for an FRC robot. Plus electric motors produce their peak torque at 0 rpm which is a big reason for a multi-speed transmission in the first place.
Zero turn drive systems ,riding lawnmowers/Bobcats, use a hydrostatic transmission on each side and a single engine powers both sides of the drivetrain. It would be really cool to build a single 6 CIM transmission that powers two hydrostatic drive units. Except for the fact that it wouldn't be FRC legal.
Argo units and other off-road atv's use a mechanical version of a zero turn system. There are trade offs in the ability to vary the turning speed of the inside and outside tires. Read more below.
http://www.argome.com/recreational/w...etaila3d1.html
In the end, an FRC dual transmission tank drive train is the lightest, least complicated option.