"Kieran" wrote in message
news:j1tUd.66306$8a6.13749@trndny09...
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.
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.

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.


Actually, it should be quite managable, seeing as how the paddle is a line.
You only need two points to track all the motions of the paddle shaft, and
two more on the sides of the blade to track the feather. Everything else
follows.

Seems like someone out there must have some sort of pressure plate: two
sheets of material with a lor of sensor points between. Put one on the blade
and get a readout of the water pressure against all points of the blade at
all times. If all you are interested in is the resultant force, put a
potentiometer on the bow and brace it against a wall.

--riverman
(I love trying to sound like I know what I'm talking about)