good one - especially when you take into account the turbulence
generated by the swimmer moving through the water.  I don't think a
device attached to his body is going to give you any usable data.

So what I'm thinking is fishing line, about 4 feet of it, attached at
the waist of the swimmer, with a very small drag device at the other
end, and then you measure the force against the drag.  There is
argument for putting the electronics both at the waist-end and at the
drag-end but so long as the fishing line didn't get tangled it should
be comparable.

Also you could generate some baselines by pulling the drag through the
water at known speeds.

DougM


On Thu, Jun 21, 2012 at 11:07 PM, cdb <colin@btech-online.co.uk> wrote:
> =A0I have been asked by someone at work to come up with a device that
> provides feedback on 'thrust' power for a swimmer, namely his 14 y.o son.
>
> My first problem is defining what I'm actually measuring - I'm unsure
> whether I should consider - force, acceleration, timed position or drag t=
he
> inverse of thrust.
>
> The main thing to detect is the power the swimmer can provide due to the
> way the hands or legs are used. Pushing off from the side of the pool or
> after turning is not important in respect of movement momentum.
>
> At the moment I'm thinking one of the following sensors might be the
> ticket, but until I can decide what I'm actually trying to measure I'm
> going nowhere. Cost is not a great problem, but $50-100 is probably what
> would be considered reasonable.
>
> Sensors:
>
> Accelerometer - g-force or change in velocity or pressure.
>
> Flexible resistance wire - wired to arm and/or leg - effort equals change
> in resistance.
>
> Stretch sensor fabric - to work similar to the above but woven into an ar=
m
> or elg band to be less of a problem and drag to the wearer.
>
> I have already checked that tying his son to a spring scale is not
> acceptable! :)
>
> Any suggestions welcomed.
>
> Thanks
>
> Colin
>
> --
> cdb, =A0 22/06/2012
>
> --
>
>
>
>
> colin@btech-online.co.uk
>
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