[Jared Russell]

You have it figured out pretty well. Your basic options are open-loop (apply voltage X for Y seconds and hope that it works) or closed-loop (use a feedback device to monitor your progress towards a goal and adjust output based on that progress).

While time-based dead reckoning is by far the easiest path, you are right in that factors such as battery voltage, tractions differences, and unplanned robot interaction will muck it up.

Using a shaft encoder or gear-tooth sensor (provided in the kit) can give you a better idea of the distance travelled, but even these cannot help much in the case of wheel slip (especially when turning). You can add a gyro to help measure angular position, but things quickly get more complicated. Plus, even the best dead-reckoning feedback algorithm is going to have holes - you can't account for every possibility on the field.

Using an adaptive approach, with the camera being able to monitor an external known position (i.e. the target) is arguably the most precise method.

Still, your choice all depends on what you want to do in autonomous - if you're going to shoot for the top with the camera, then you might not need any sensors besides the camera: just drive for a second or two, then let the camera lock on and aim. If you're going for a side goal, you can pretty much do the same: drive straight, hugging the wall (you can have your robot turn slightly into it to stay against it), then after a few seconds, jettison your balls.

The more complicated and precise the task, the more a feedback mechanism (encoders, gyros, cameras) will help.