[waialua359]

While our team has not measured the voltage drop issues you have, we instead countered it by not having the ball travel a large distance from our feeder into the shooter head.
By keeping it a short consistent distance prior to shooting, we limited the amount of draw from the feeder in order to shoot the ball. All of our set points for aperture and motor speed has been based off the exact same feeder location of the ball prior to shooting.
I found at least a couple of teams that asked us about such issues with their own robots, when we participated in Hawaii this past weekend.

A simple solution is adding a VEX touch sensor.
We also have a custom dashboard indicator that tells our operator once the shooter wheels are at the max velocity at our particular location on the field.
If you get to watch some of our matches this past weekend on JustinTV, you'll find it works quite well, where we hit consistent shots, and quickly between shots.