I was thinking of exactly such a system a while ago (with a one-way bearing), but the fatal problem with such a system is that it only works in one direction - and FIRST robots almost always have drivetrains that have to go equally in either direction. There may be a way to make it work with some complicated gearing and multiple one-way bearings, but if so, I don't know what it is.
-Ian Mackenzie
Team 188
Woburn Robotics