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


--

In article , Carl Douglas
wrote:


Sounds a nice easy problem, only slightly more difficult than the one
about life, the Universe & everything. Have fun, Keiran!


So, there's the answer!

42



Allan Bennett
Not a fan of fish

--

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

--

Ah, we have a D. A. fan. Yes of course 42. I should have thought of that.

Ken

"Allan Bennett" wrote in message
...
In article , Carl Douglas
wrote:


Sounds a nice easy problem, only slightly more difficult than the one
about life, the Universe & everything. Have fun, Keiran!


So, there's the answer!

42



Allan Bennett
Not a fan of fish

--

"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.

"riverman" wrote in message
...

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!

I mean, Kieran!!

In article , Wolfgang
wrote:

"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. :(

Good stuff, Wolfie - you're half way there to understanding the point that
was made.

But you forgot to mention this wall and the bungee...

Wolfgang
who, apparently, is no physicist.

....nor a rocket scientist, don't forget...

Allan Bennett
Not a fan of memory lapses

--

In article , riverman
wrote:

"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?

Nope. I don't want to quantify anything - Kieran does. But, he wants to
measure force on the shaft *during* a paddle stroke, which will be different
to the forces during a tethered stroke or when braced against a wall or on an
erg or whatever. Just try it.

Ultimately, all the variables you mention - plus a load more - will finish up
as force on the immersed blade, which can be recorded using simple (these
days) tensiomentric devices.


Allan Bennett
Not a fan of superprotractedmegaovercomplication

--

"Allan Bennett" wrote in message
...

Good stuff, Wolfie - you're half way there to understanding the
point that
was made.

I like to think I'd get there faster if someone would identify it for
me.

But you forgot to mention this wall and the bungee...

My apologies. Consider them hereby mentioned.

Wolfgang
who, apparently, is no physicist.

...nor a rocket scientist, don't forget...

I won't......well, I'll try not to.

Allan Bennett
Not a fan of memory lapses

Nor am I.......um.......if memory serves.

Wolfgang