"Michael Daly" wrote in message
...
On 27-Feb-2005, "riverman" wrote:

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.

You need three points in total to measure all the motions of the
paddle.
If you have two on the shaft and one off the shaft (say, normal to
the
mid-point) you can determine what's going on.

I thought about this and figure that measuring the motion of these
points is more trouble than it's worth. I'd be inclined to try the
following:

A six-degree-of-freedom accelerometer system (all in a box costs a
few hundred US$) attached to the paddle shaft. This will measure
all accelerations of the paddle in every direction. A six-channel
A-D converter actually costs more than the accelerometer.

A computer that integrates the above data from a starting point
(say, a paddle "saddle" as a zero-reference point on the deck
in front of the paddler). This can be used to determine the
position and orientation of the paddle at every point in the
experiment. Can be done in real time or after the fact.

A seat mounted on a three-support frame. This would be statically
determinate and will allow all paddler forces to be measured
directly from strain guages in the seat supports. The "seat"
would in fact be a frame that includes foot support, since
foot forces can be a considerable component of the paddler's
actions. The problem with this may be reinforcing the kayak
to allow all forces to be transmitted thru only three points
to the hull. You'd have to also design the seat frame to
have very little friction for certain degrees of freedom
at each support in order to have it determinate.

The geometry of the seat relative to the paddle starting point
can be measured accurately and then all paddle positions are
known in time. Forces at the three seat supports can then be
resolved into the forces exerted by the paddle.

All of this sounds terribly complicated to me. Why not just tether
the stern of the boat to the measuring device of choice anchored to a
dock?

Wolfgang