Our team sank 60% our shots in practice at our field in the top basket. Competition field, in the 7 matches out of 10 we were mechanically okay we shot around 4-8 shots per match and sank 3 all tournament, shooting almost all of our misses 3-4 feet high. The worn out balls squish easier than the ones on the field I believe (trusting the word of my drivers who felt both balls, and the physics that make sense). Our targeting system is unaffected by lighting changes from practice field to field, as evidenced by saving images to the cRio in match to check to see if that was the problem.
The physics behind this makes sense. If a ball is squisher, it will compress more easily. Since less force is needed to compress it, it will mean less normal force between the wheels and the ball, less frictional force, and less speed coming out. A firmer ball will take more force to compress to the same dimension, which means more normal force, and therefore friction, between the ball and the wheel leading to an increase in muzzle velocity. We're fairly certain the angle of our shooter didn't vary from practice field to competition, so the only thing is speed...which we can only attribute to the balls. We went to the practice field at competition and used our own balls (worn out and squishy) to shoot, no problems! So we need to find some way to account for that discrepancy.
picture of our robot:
http://www.chiefdelphi.com/media/photos/37578