[Donut]

Something I just thought of about an hour ago that you might also want to consider. It still needs to be calculated, but rather than changing the angle (as most everyone on here has said they plan on doing) that the ball is released at, why not keep the angle constant and vary the speed at which it leaves the robot? It gives you the same desired effect, and saves you one motor or servo (and who knows how much weight).

This is going to take alot of testing to get right. Air resistance you could factor in, but spin will be hard to, especially if/once balls start getting deformed from extensive use (eventually this form is going to squish!). Deformations can also effect how much contact the ball will have with the launcher and change speed.