[Kevin Sevcik]

As noted, the rotational inertia of most all gearboxes in FIRST are negligible. And if you lightened the gearbox with everything else the same, your max speed would remain the same, though the robot would accelerate slightly faster. The best way to think about it is as a division of kinetic energy. Assuming you have a flywheel attached such that it spins faster the faster your robot moves, the flywheel would store some amount of rotational kinetic energy for every Joule of translational kinetic energy stored by your robot moving forward. With a standard gearbox, it's probably something like .01 J of rotational energy for every 1 J of translational. With a big flywheel, you'd be storing more in the flywheel, and a comparatively smaller amount of every J from your motor would be going towards actually moving the robot forward.

To correct one error I've sen in this thread. The top speed of your robot does not depend on the max RPM of the motor. It depends on the friction in your drivetrain. The friction represents a torque that must be subtracted from the torque developed by the motor before you start firguring the acceleration of the robot. So at some point, the torque put out by the motor equals the friction torque, and your robot stops accelerating. Since the motor is putting out mre than zero torque, this isn't going to be the no-load speed.