Some Background I am working on a soccer robotics project called RoboCup (perhaps people here have heard of it), which revolves around building a fleet of autonomous soccer robots that play against each other (league website - http://small-size.informatik.uni-bremen.de/ [Broken]). The kicking mechanism on the robot is a solenoid. A moving core impacts a ball to give the ball a speed of 8 to 10 m/s. The Question The big question here is whether a round solenoid or a rectangular solenoid could achieve a faster ball speed given the same volume. I realize there are a lot of design parameters, but I'm just having trouble trying to determine relatively, which geometry would better suit my purpose. The round solenoid would just be a cylindrical shape with a cylindrical core moving back and forth. A rectangular solenoid (the wires are wound in a rectangular shape, rather than using wires of square cross-section) would have a flat core that slides in and out. I guess the most important performance metrics here are to maximize energy transfer into the ball, while minimizing the size of the solenoid (I guess transferred energy divided by solenoid volume is a good metric here). I greatly appreciate the insight from the users on this forum! If my question isn't clear, I'd be happy to clarify.