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An analysis of Iron Byron swinging either bottom-up or top-down


The same but not quite the same


Invisible exertions



It is intriguing to have instructors teach to swing form the top and yet when one looks at their swing they have no early dissipation of angles. One has also instructors, such as LB, teaching swinging and hitting with a very different approach and yet one can't distinguish any difference in their swing when demonstrating.
  
Is this all simply in the domain of  feel vs real or is there perhaps more to it ? Surprisingly even in the case of Iron Byron, really a stripped down bare bone golfer, it is possible to show some light on these questions without the ambiguity normally encountered when considering a real golfer.




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Our Iron Byron has only two torques which with it can act on the arm/club ensemble. We will generate two swings, with very different torques, but yet with identical result. One could say a bottom up swing vs a top down swing even for this very simple double pendulum robot golfer.

The figures on the left side are concerned with the 'bottom-up' Iron Byron golfer. The figures on the right side are showing the prowess of the 'top-down' Iron Byron golfer. This makes for ready and easy comparison of these two swings.

In the 'left' swing we use torque2 only to model a 90 deg dead stop, Fig1a and 3a, to prevent back knifing of the shaft in the early part of the down swing. Hence this torque does not do any work as there is no relative motion between the two segments.

The only work done in this particular swing is by the inner torque1. One could say that this corresponds to a golfer swinging from the bottom-up or inside-out. To make things limpid it is made to have a constant value, Fig2a.

In the 'right' swing, Fig1b, we have Iron Byron exert a constant positive torque2, Fig3b, and use inverse dynamics to derive the inner torque1, Fig2b, required to make the two swings identical. Hence here we could say that Iron Byron swings top-down or outside-in.  

The dashed vertical red line segment in the figures indicates time/location of impact.



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The torque for the 'left' swing has been simply taken as a constant as shown in Fig2a. Applying the moving constraint derived from the 'left' swing results in a very different torque1 for the 'right' swing, Fig2b. The torque starts modestly but is increasing substantially towards impact.



"top_bottom_3_3.gif"



Fig3a shows torque2 modeled to constitute a dead stop. Since there is no relative motion between the two segments there is no work done, hence a passive dead stop such as a fully cocked wrist. In Fig3b is shown torque2 as chosen for the 'right' swing, a constant torque of 9.5 Nm.



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The two swings as shown in Fig4a and Fig4b do appear indeed identical. Some might expect it to be simple a copy/paste operation. However, it is not, they are really two swings derived with very different time histories for the two torques as detailed above.


One could think of the 'left' swing as having the hands/wrists as the primary motivation for the down swing whereas the 'right' swing could be thought as having its primary motivation to be the inside core. As shown above one can make them to produce identical swings.

The moving restraint imposed on the 'right' swing is independent of time. Slow or fast, the moving restraint imposes for each particular angle for the inner segment a particular angle for the outer segment. We can choose one of the two torques and let the restraint determine the other torque.


Concluding remarks

Even if above concerns an Iron Byron type golf robot, therefore not a real golfer immensely more complex, it still shows that even a very simple Iron Byron golf instructor could mystify his students telling them to use active wrist torque throughout the whole down swing, and indeed actually doing it, but likely not knowing himself that it takes a rather special torque, developed at the core, for his students to imitate his nice looking swing.

The bewildered student goes down the line to the next Iron Byron teacher and takes his chances for another lesson. This teacher however emphasizes strongly that the swing should be done from the inside-out, with passive wrists. The student is now getting utterly frustrated, one is telling him to swing from the top and the other is telling him to swing from the  bottom.

Once back at home and looking carefully at the slowed down swing sequences of these two instructors the student is getting even more mystified - they are indeed identical. But, by Jove, their very authoritative instructions and comments definitely were not.

If even in a world made up of very simply double pendulum golfers and instructors it is possible to be getting completely confused by the matter of feel vs real then it should be almost natural that it happens all the time considering the complex human machinery constituting the real world of golfers and instructors.

Mandrin