# Solenoid geometry question: circular cross-section or rectangular?

## Main Question or Discussion Point

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.

Last edited by a moderator:

## Answers and Replies

Related Electrical Engineering News on Phys.org
It won't change much. A circular section is a bit better since it reduces the wire length for a given flux - but above all, it's easier. If you wind several layers on a square mandrel, the coil ends round anyway, unless you usespecial methods.

If you want dynamic actuators, hydraulics is better than pneumatics which is better or equal to the best electric actuator, which is a voice coil motor. Though, you seem to depict a plunging core, which is seriously slower than a voice coil motor.

Or could you use spring that you compress slower with an electric motor?

Thanks for the reply. Just wondering, how do you come to that conclusion of how both geometries are similar? I've been giving that part a lot of thought and I can't determine a good reason on why the two geometries would have a similar performance.

Interesting suggestion you have on the pneumatic actuators. That is definitely something I had never considered previously. Other teams in the league also use solenoid for the same purpose and I guess that must be why I never considered it. It seems that everybody in the league has had their design converge to all using solenoids.