In article , riverman
wrote:

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.

Unfortunately, like all the suggestions about tethering the boat, this idea
misses the point by a mile: Kieran wants to measure the forces during a
paddling stroke - paddling against a resistance is just not the same.

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

....keep trying...


Allan Bennett
Not a fan of immovable objects

--

"Allan Bennett" wrote in message
...
In article , riverman
wrote:

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.

Unfortunately, like all the suggestions about tethering the boat, this
idea
misses the point by a mile: Kieran wants to measure the forces during a
paddling stroke - paddling against a resistance is just not the same.

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

...keep trying...


Allan Bennett
Not a fan of immovable objects

--

Well, okay but I was hoping that you'd come to this last point on your own.

You've got too damn many variables, Allan! You cannot run an experiment when
the variables include feather, fetch, grab, speed of stroke, blade depth,
variations of applied power, assault angle, retrieve distance and time,
stroke time, etc etc etc. Add to that a human doing the motions, and even
an isolated variable will have abberations. There is absolutely no way to
determine cause and effect if you cannot identify the role of a single
variable.

You need to isolate variables. Build a jig that will hold a blade and rotate
it in a circular motion. Place a paddle in the jig, and adjust the feather
angle, then let it wind out a few dozen times while you measure the pulling
effect on a rope tethering the boat. Change the feather angle, and go at it
again, until you have a 'feather angle vs forward force' graph. Change the
length of the paddle shaft until you have a 'blade depth vs. forward force'
graph. Change the rotational velocity until you have a 'stroke speed vs.
forward force' graph. Etc.

Then build a jig that will hold a paddle and move it horizontally with the
shaft vertical, lift it out and replace it a few feet forward. Maybe
something on a caterpillar tread. Place a paddle in this jig with no
feather, and run this several times and vary the feather variable until you
have results. Then change the speed, the length of the stroke, the angle of
the paddle, etc.

The build another jig that will do something else, and run a host of tests
on that.

When you are done, you need to solve each of these equations for the
representative curve, the K factor, and then meld them together into a
joint/inverse relationship equation that takes all the variables into
account with a single K.

And good luck!! IIWY, I'd identify 3 or 4 variables and call it a day. Just
think of all the minor adjustments a paddler makes within a single
stroke...and you want to quantify THAT?

--riverman

"Allan Bennett" wrote in message
...
In article , riverman
wrote:

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.

Unfortunately, like all the suggestions about tethering the boat,
this idea
misses the point by a mile: Kieran wants to measure the forces
during a
paddling stroke - paddling against a resistance is just not the
same.

Evidently I've gone and bought myself a bad boat. It resists
movement. However, this is probably not as bad as it sounds. It
turns out that we also have peculiar water in my neighborhood......it
resists the motion of my paddle.

Wolfgang
who, apparently, is no physicist.

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


--

Allan Bennett wrote:
In article j1tUd.66306$8a6.13749@trndny09, Kieran
wrote:

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.

Hmmm... this seems to be the part I'm missing. How do you get power
without knowing the path of the force?

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.

Thanks for the reference. I'll see if I can find that publication.
Would that be a book or a journal article?

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?

Trying to come up with a master's thesis for my degree in biomechanics.
A research prof here has an ongoing project that considers at a high
(systems) level the energetics of different forms of human locomotion
through/in/on water, including surface swimming with/without fins,
submerged (e.g. scuba) swimming, rowing, and kayaking. There's very
little published research that we can find on kayaking, so that's the
part I'm tackling.

Thanks for your input!
-Kieran

On 10-Mar-2005, Kieran wrote:

Hmmm... this seems to be the part I'm missing. How do you get power
without knowing the path of the force?

Determining the moment in the shaft at some point allows you to resolve
the force at another point (say, centroid of area of the blade). Knowing
the paddle motion, from the video analysis you can do, will allow you
to determine the velocity of that centroid. Hence the power out. Since
power is a scalar, not a vector, you don't have to worry about direction.

However, that is total power in, not power that drives the kayak forward.
That is, if you calculate (estimate) the power to drive the kayak (total
hull resistance times hull velocity), it will be less than the power that
the paddle generates.

Mike

Kieran:

As a person who did considerable white water kayaking in the 60's
(since then it's been mostly C-1 and rafting), plus a combined-fields
background (B. of M.E. and Ph.D. physics), I hope I can offer some
constructive comments.

First, let us just consider measuring the forces in sufficient detail.
I agree with the suggestion of Carl Douglas on February 28 that strain
gaging the paddle shaft is probably the most effective way to go.

Strain gage arrays can be designed to do each of the following:

(1) Measure flexursl (bending) moment.

(2) Measure axial force.

(3) Measure perpendicular (shear) force.

(4) Measure torsional (twisting) moment.

Incidentally, I prefer using "arrays" instead of "rosettes" because a
rosette most often is used to denote two or more adjacent strain gages
mounted on the same backing sheet. "Array" is more general, as it can
also include strain gages mounted on opposite sides of the paddle
shaft.

Thus, a combination of strain gage arrays between the paddle blade and
the paddler's hand can measure all necessary force components. A
similar combination of arrays, rotated by 90 degrees with a feathered
paddle, would be mounted between the other paddle blade and the
paddler's corresponding hand.

This leaves the question of forces in the paddle shaft between the
paddler's hands. We should not assume that these are zero. Strain
gage arrays can be mounted at the middle of the shaft. Again, all of
the above (1-4) can be measured. Measuring flexural moments at the
midpoint can even resolve possible flexural moments exerted by the
paddler's hands.

Thus, we are talking about a total of 12 strain-gage-array measurement
channels. But with all of them, the forces and moments on the
paddler's hands become statically determined. Possible extrapolation
to forces at wrists, elbows and shoulders remain separate problems.

Using strain gages sounds deceptively simple. At risk of telling you
what you already know, let me recommend "Strain Gage Users's Handbook"
(1992) edited by Hannah and Reed, most highly. It is published by the
Society for Experimental Mechanics, Inc. Bethel, CT. Among other
things, it is not advisable to mount strain gages on plastic or
composite surfaces. This has to do with heat-sinking. Metal surfaces
are best. Thus, if the kayak paddle has an aluminum tube core (as many
do), suggest stripping the outer, plastic layers off before installing
the strain gages.

Regarding the problem of velocity measurements (to get the power), I
suspect that the video method which you proposed would be most
effective, especially as I got the impression that some people in your
department already have some experience with that. The alternative
idea of using 3-D arrays of six accelerometers is also intriguing.
Effects of error propagation in integrating acceleration can induce
serious inaccuracies, unless great care is exercised.

Overall, my reaction is the following:

(1) The project is certainly feasible, and has exciting potential.

(2) Considering its scope (if done thoruoghly) it may be too much for a
Master's thesis, and more appropriate for a Ph.D. thesis. You may wish
to talk with your professor about that.

Please feel free to contact me directly.

Andres Peekna
Innovative Mechanics, Inc.
5908 North River Bay Road
Waterford, WI 53185-3035




Kieran wrote:
Allan Bennett wrote:
In article j1tUd.66306$8a6.13749@trndny09, Kieran
wrote:

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.

Hmmm... this seems to be the part I'm missing. How do you get power
without knowing the path of the force?

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.

Thanks for the reference. I'll see if I can find that publication.
Would that be a book or a journal article?

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?

Trying to come up with a master's thesis for my degree in
biomechanics.
A research prof here has an ongoing project that considers at a
high
(systems) level the energetics of different forms of human locomotion

through/in/on water, including surface swimming with/without fins,
submerged (e.g. scuba) swimming, rowing, and kayaking. There's very
little published research that we can find on kayaking, so that's the

part I'm tackling.

Thanks for your input!
-Kieran

Why not measure the HR of the engine? I've read that the well trained
athelete can output something in the neighborhood of 1/4 HP. All the
variables of measuring the work accomplished would not change the power
rating of the motor, if it is power you are after! TnT

On 27 Feb 2005 06:35:50 -0800, "Tinkerntom" wrote:

Why not measure the HR of the engine? I've read that the well trained
athelete can output something in the neighborhood of 1/4 HP. All the
variables of measuring the work accomplished would not change the power
rating of the motor, if it is power you are after! TnT

Different muscle groups may output different amounts of energy/power,
whatever the potential of the CV system.

Happy trails,
Gary (net.yogi.bear)
--
At the 51st percentile of ursine intelligence

Gary D. Schwartz, Needham, MA, USA
Please reply to: garyDOTschwartzATpoboxDOTcom

In article .com, Tinkerntom
wrote:
Why not measure the HR of the engine? I've read that the well trained
athelete can output something in the neighborhood of 1/4 HP. All the
variables of measuring the work accomplished would not change the power
rating of the motor, if it is power you are after! TnT

HR is a measure of sympathetic stimulation and oxygen demand by the working
muscles. It will not give an accurate assessment of power, esp when
anaerobic fibres become significantly invloved... Those who have used a HRM
will also have noticed that HR can remain high even when the workload is
reduced to plodding pace or slower, plus weekly or daily variations.

Allan Bennett
Not a fan of horse-sense

--