Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
Kieran writes
Tinkerntom wrote: Force on the paddle shaft, at the handgrip. Makes me think of a big torque wrench. Do you get any deflection of the paddle shaft while paddling? Use a smaller shaft until you do, Take video, or measure the deflection of the needle! Then in the lab, measure the force needed to duplicate the deflection. You should then have an idea of what the possible force exerted on the shaft would be for a particular paddler. The potential force would be based on as wolfgang points out the effectiveness of the engine mount, the paddlers seat and feet, the grip, and other loss of efficiency factors that could be isolated for significance. TnT The problem is not how to measure the moment (torque) on the shaft. Strain guages have been around for ages that will allow me to do that, and I'm well familiar with how to implement them. The problem is determining power from that force. The force balance in the kayak system is weird, as there is no fixed pivot point on the paddle. So, the pivot point is a "virtual" one. I'm making progress, but still wonder if anyone has done this already. The only way I can see to determine power at the hand grip is to record 3D kinematic video of the motion, so that the actual 3D vector of the handgrip velocity is known. Then Power=FxV. But I wonder if there's a better/simpler way to do it. I did find a paper (Aitken, 1992) that measured paddle shaft torque (bending) with strain guages, then used the hull velocity through the water to get power. I don't see how this is valid, though, since hand velocity is not equal to hull velocity. But then I suppose it would depend on what your frame of reference was... Hmmmm.... Any other bright ideas out there? :-) Keiran - Your getting lots of feedback, but the complexity of the problem is vast and the simplifications on offer may be too simplistic, although you've made that point in some you've answered already. Trying to assess fluid drag on the boat from towing measurements is not going to give a great answer, since no kayak goes in straight lines. And even if you could measure a more accurate power loss for the hull that gives you no handle on the power losses around the immersed paddle. A paddle is probably more efficient than an oar, but how efficient is it, & how does its propulsive efficiency vary through the stroke? Could one "catch" all the energy added to a finite but significant volume of free water surrounding the path of the paddle stroke? Are there ways to track the 3-D motion within that volume over time (it sounds like a real-time tomography problem, perhaps done by laser scans using suspended reflective particles), & feed that back into a CFD program to sum up momentum transfers and frictional losses. Now, if you could strain gauge a paddler........ It'd be great if the means existed. Then you'd be able to measure the forces & speeds of action at every bodily joint. Does that mean you'd have to build a robotic paddler & tune him until he imposed the same loads & speeds of action as a human on real paddles in a real moving boat? Or is there any feasible way to take such direct measurements? The answer may still be 42, of course. Good luck there - 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) |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
rec.boats.paddle sea kayaking FAQ | General | |||
rec.boats.paddle sea kayaking FAQ | General | |||
rec.boats.paddle sea kayaking FAQ | General | |||
rec.boats.paddle sea kayaking FAQ | General | |||
rec.boats.paddle sea kayaking FAQ | General |