Kayaking power

Allan Bennett wrote:
 > In article <j1tUd.66306$8a6.13749@trndny09>, Kieran
 > <URL:mailto:kc_news@sonic.net> 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<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Kayaking power 

Allan Bennett wrote:
 > In article <1109514950.780220.183160.DeleteThis@f14g2000cwb.googlegroups.com>, Tinkerntom
 > <URL:mailto:tnksng@qwest.net> 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
 >

The P.I. I'm working with is actually a systems physiologist, and
currently uses metabolic estimates of power and economy (HR + O2
consumption) for kayaking. We want a more direct measurement.

-Kieran<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Kayaking power 

Allan Bennett wrote:

 > There has been some tensiometric analysis carried out with strain gauges on
 > the shaft (see The Canadian Canoe Association Coaching Manual; The Science of
 > Canoeing, Richard Cox, ISBN 0 95118931 14). The work has
 > been repeated from time to time (I've just dismantled my own kit, sorry).
 > All the results are similar, but the usefulness is negligible, IMO.
 >
 > However, I suggest you set up a paddling ergometer which can give you the
 > data you require w/o the vagaries of water and weather conditions.

Our lab actually has a very large annular pool where this experiment
would take place, so it would be a fairly controlled environment. I'll
check out the Coaching Manual you referenced above, thanks.

 > Allan Bennett
 > Not a fan of square wheels

Yeah, neither am I!

-Kieran<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Kayaking power 

Anthony Garcia wrote:
 > If you want motive power or P = {F}*{V} then you would wish to measure
 > either the reaction forces of the Kayaker against the boat and/or the
 > tractive force of the boat (use a line with constant tension and measure the
 > velocity.)
 >
 > If you want the forces on the paddle to generate force vs position and/or
 > time it will get much more complicated but not impossible. Try using strain
 > gages on the paddle shaft with the data synchronized with video. You can
 > (with much labor) get position, force and velocity.

Yes, this is exactly what I assumed needs to be done. We have the
hardware and software to do 3D kinematic video analysis, but I was
wondering if there was ever a simpler method devised.

 >
 > There is software already in use that can provide many of the tools you
 > need. You may need to spend $$ for it though and the learning curve is
 > probably steep.

Which software is this? I'd appreciate a link or reference. There is
money to be spent on this... not infinite amounts, but some....

thanks,
Kieran<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Kayaking power 

On 10-Mar-2005, Kieran <kc_news DeleteThis @sonic.net> 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<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Kayaking power 

Tinkerntom wrote:
> Allan Bennett wrote:
>
>>All the results are similar, but the usefulness is negligible, IMO.
>>
>>However, I suggest you set up a paddling ergometer which can give you
>
> the
>
>>data you require w/o the vagaries of water and weather conditions.
>>
>>
>>Allan Bennett
>>Not a fan of square wheels
>>
>>--
>
> On 3/2, I posted describing the paddle as a large torque wrench. I have
> a background in mechanics and have used torgure wrenches. Is this what
> you are mentioning for strain gauges?

Yes, your idea of using a torque wrench is essentially the same thing
that a strain guage would give. Except the strain guage would be much
more precise, and more accurate.

>
> You say the usefulness of of the measurements are negligible, can you
> expound? TnT

I too wonder what Allan meant by this comment.

-Kieran
 >> Stay informed about: Kayaking power 

Michael Daly wrote:
 > On 10-Mar-2005, Kieran <kc_news DeleteThis @sonic.net> 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.

Yes, all this I already knew... basically you're saying you DO need to
know the path of the force to get power. It seemed that Alan was
implying there was another way, just by knowing the force-time relationship.

 > 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.

Actually, that's kind of the point. We want to know how much power the
paddler develops and puts into the paddle.

-Kieran<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Kayaking power 

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

<innmech.RemoveThis@wi.rr.com>


Kieran wrote:
 > Allan Bennett wrote:
  > > In article <j1tUd.66306$8a6.13749@trndny09>, Kieran
  > > <URL:mailto:kc_news@sonic.net> 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<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Kayaking power 

"Michael Daly" (michaelDaly@foo.bar) writes:

 > 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.

a lot of the wasted power is dissapated as heat in the water, kayak
paddlers being one of the major causes of global warming. if you plot the
increase in the fad of kayak paddling with the increase in global temerature
you get a correlation of 0.999


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Kieran <kc_news.RemoveThis@sonic.net> 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
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Carl Douglas (Carl@carldouglas.co.uk) writes:

 > 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?

Place the strain guages on a dummy and tow the kayak backwards through the
water. Do this many times, each time with the dummy in each successive
position in the paddle stroke, similar to making an animated cartoon.


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