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riverman writes
"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. 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. Since it is more the reduction in pressure on the convex back of the paddle which moves the boat than the increase on concave face, you'll need a sensing surface on both faces. Even then you'll measure pressure but not shear (frictional) forces. Might be better to measure the forces at the paddle neck directly by means of strain-gauge rosettes. Then there's angle of shaft, direction & velocity of blade motion & (variable) location of centre of pressure to consider. Sounds a nice easy problem, only slightly more difficult than the one about life, the Universe & everything. Have fun, Keiran! Cheers - Carl -- Carl Douglas Racing Shells - Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK Email: Tel: +44(0)1784-456344 Fax: -466550 URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers) |
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