*4.1. Hypothesis*

The reluctance coil gun previously described and used in robots at the RoboCup has been simulated using Matlab Simulink. In this study, we focus on optimizing the inner structure of the coil gun and especially we aim at finding the optimal number of coils and the optimal instant and duration of triggering for each coil in a sequence.

Optimality is not only focused on the ball speed which must be as important as possible, but also on the reliability and robustness of the triggering system, which can be very sensitive to a small change in the triggering delay when several coils (especially 3 or 4) are used.

This last point is important because we have decided of not adding an observer of the plunger position in the system such as a set of infrared light barriers. This choice has been done considering the mechanical difficulties for inserting sensors inside the coil gun structure, and the issues about robustness it can raise due to the huge impacts and vibrations on the EML structure. Instead of that, a simple and robust open loop driving has been chosen, each coil being commutated during a fixed time and with a fixed delay from the start of the sequence. Considering that the initial conditions of the plunger position are always the same ones (this is true because the plunger is returned to its initial position by an elastic restoring force), the ball speed has been measured to be almost the same at each shooting sequence.

This paper does not focus on optimizing the initial position *xinit* of the plunger, and the length *Lext* of the non-magnetic extension of the plunger, as done in [12]. In this study, we started using the results presented in [12]. However, in a final step, a fine optimization has been done for getting the best possible solution on both parameters.
