In article j1tUd.66306$8a6.13749@trndny09, Kieran
wrote:
Bob Arledge wrote:
Why not put a strain gauge on the paddle shaft just below the paddler's
hand. This would give you the moment at that point, so the force would be
the moment divided by the distance between the strain gauge and the
centroid of the paddle blade.



That's the general idea, but because the paddling motion is 3-d, it's
not very easy to determine power just from the strain in the paddle
shaft.

The flex in a paddle-shaft will be a reflection of all the forces acting upon
the blade in the water. Using the force profile: t v deflection) and
suitable calibration, it will be possible to determine the power.

You need to know instantaneous velocity (direction and magnitude) at every
moment. In a fixed-pivot environment like rowing, you can just put a
potentiometer on the oar-lock. But the kayak/canoe paddle has no fixed
pivot point. So, I imagine that a virtual pivot point would have to be
derived via 3-d kinematic video analysis.

It seems there is a virtual point (see Plagenhoef, 1979 and others), just as
there is a virtual point where all the forces that propel the boat seem to
meet - a valuable tool for those athletes with adequate imagination.


I haven't yet sat down and done a free-body of the system, but in my
head, it seems like it's going to be an indeterminant system... not fun.

...and the ultimate purpose?


Allan Bennett
Not a fan of virtual science


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