For those who are not aware, there is a robotics league called RoboCup. This league builds robots that are completely autonomous with the challenge to compete against humans by 2050. This league has been around for some time and they really have perfected kicker design. If you are confused in how to design a kicker, I highly suggest you do a search on Google or Youtube for RoboCup Medium Size to see some of these robots in action. Additionally, some of the teams websites have published papers that talk about their designs. Keep in mind that some of these designs may not be legal per the FIRST rules. Here is a link that might help you out.
Robocup Shooting Mechanism