The Butterfly Kick - First Idea

After our initial research, we observed that the motion could be simplified to a three section movement for a first approach. Those three sections are: from feet to knees, from knees to waist and from the waist up. We measured ourselves to obtain the proportions between each sections to build the most realistic model possible:

 

 

After a little rounding we came to a conclusion that the lower two sections are of almost the same lenght and the upper one is 3/2 of one of the first two. We didn't separate the upper sections into smaller ones beacuse we are concentrating on the kick.

 

After this measurement we build this frame in which the user should lay facedown with the head on the right side. Please note that the natural position is with the head facing down and the abs and the legs are flexed and relaxed, this is because the lower two sections are pivoted in the exact centroid but the upper section produces a negative moment produced by the extra weight and lenght on the right side, we will have to assume the body has uniform density for this model. The crossing beams at the lower legs should be seen as if the one that is up si where the legs will really be laying, the idea is to make several beams that cross each other like zigzag.

 

Since the main effort comes from the abdominal muscles, the objective is that the user pushes the machine down with that part of the body and lift the legs in an stretching movement. Naturally, the waist cannot rotate a lot backwards so we added some limits for the beams at the bottom part.

 

The "W" array at the bottom is for compensating the variable distance between the unions of the main beams as they rotate; the middle axle is fixed in space by a triangle and the other two axles separate from the center as the abs push the right union down. One side effect is that those points are rotating rather that translating horizontally as it should ideally be, that's why we put large gray beams at the bottom so the vertical movement is attenuated in that range.

It is possible to make the same machine hanging from the ceiling, but that requires modifing the training space. We are working to include the ankle movement and the final kick of the cycle on the next try.

Erick & Luis