[herbbread]

So I've been thinking for a while on ways to measure the force on a paddle (like canoe paddle). I do a lot of dragon boating (like a giant canoe with 20 people in it) and I wanted a way to be a little bit more quantitative about performance on our team. I've researched a few things and it seems that the best way to do this might be to attach a strain gauge to the shaft of the paddle and measure bending of the shaft as a proxy for actual force. I've also though of mounting some type of force sensor on the paddle itself, but I read one small journal article detailing a groups experiment with a force sensor and found that simply entering the water with the paddle marked the biggest change recorded force.

I was imagining that whatever signal I record would go into a small waterproof box mounted on the shaft with electronics and a bluetooth transmitter to send the data to my phone. I have little experience with putting together such electronics, so I wanted to ask to see if anyone might have any idea how much work putting together something like this to be, how much it might cost, and any recommendations on how to go about it. Thanks in advance!

[Schrödinger's hat]

herbbread, on 2 October 2011 - 07:09 PM, said:

So I've been thinking for a while on ways to measure the force on a paddle (like canoe paddle). I do a lot of dragon boating (like a giant canoe with 20 people in it) and I wanted a way to be a little bit more quantitative about performance on our team. I've researched a few things and it seems that the best way to do this might be to attach a strain gauge to the shaft of the paddle and measure bending of the shaft as a proxy for actual force. I've also though of mounting some type of force sensor on the paddle itself, but I read one small journal article detailing a groups experiment with a force sensor and found that simply entering the water with the paddle marked the biggest change recorded force.

I was imagining that whatever signal I record would go into a small waterproof box mounted on the shaft with electronics and a bluetooth transmitter to send the data to my phone. I have little experience with putting together such electronics, so I wanted to ask to see if anyone might have any idea how much work putting together something like this to be, how much it might cost, and any recommendations on how to go about it. Thanks in advance!

What about the rowlocks? Some kind of piezo sensor where they attach to the boat might work.
That is if you can modify the boat.

W/ regards to the oars, a strain gauge sounds like the way to go.
One thing to think about is angle, though. If the flex isn't along the same axis as you calibrate your strain gauge it won't work. If your rowers rotate the paddle as they row you may need two which are at righ angles to each other.

For your transmitter, I have seen an all-in-one package that transmits on a custom frequency used in one of the engineering teaching labs I was tutoring. They looked like the kind of thing that would be pricy, though. I also don't know where to get them. The software was also proprietary and windows only.
If you're adept with this type of thing, you could probably put something together from pieces yourself. Maybe find a similar project (measuring voltages and sending them over bluetooth) and just switch out the source of the voltage.

[herbbread]

Thanks for the advice. So the unfortunate thing about dragon boat paddles is that they aren't oars and so aren't attached to the boat and have no fixed pivot point. They're used just like canoe paddle where the paddler has to hold onto the whole paddle (much less efficient than rowing, but I say a lot more fun).

So are there strain gauges that are sensitive to such small changes as might occur in a bending paddle? And thanks for that site, it looks really useful. I'll take a look at what I can find and see how much experience I might need to put something together as cheaply as possible.

[Schrödinger's hat]

herbbread, on 3 October 2011 - 01:05 PM, said:

Thanks for the advice. So the unfortunate thing about dragon boat paddles is that they aren't oars and so aren't attached to the boat and have no fixed pivot point. They're used just like canoe paddle where the paddler has to hold onto the whole paddle (much less efficient than rowing, but I say a lot more fun).

So are there strain gauges that are sensitive to such small changes as might occur in a bending paddle? And thanks for that site, it looks really useful. I'll take a look at what I can find and see how much experience I might need to put something together as cheaply as possible.

Also bear in mind that any calibration you make on them will tend to wander quite frequently.
Also the data will depend on where they are held.

The tennis racquets used in that engineering course I was talking about require calibrating every time they are used, and only seem to give reasonable data one in three times.
Maybe talking to an engineer might be worthwhile?

[CaptainPanic]

The thing that you need to know is the force on the part of the paddle that is in direct contact with the water, and the duration of the force. In other words: a curve of the force on the paddle over time.

Due to the curved motion of the paddle in the water and its shape, the force isn't the same anywhere.

It seems to me therefore that the only place that you can reliably measure the force applied is just above the broad part of the paddle.

[herbbread]

Thanks for the help guys. I'll look a little more into it and see what I can find. If it would require constant calibration, and the measurements weren't that reliable, I'd be more skeptical about any results I actually obtained, and it might not be that useful for what I had in mind. Thanks again.

[Externet]

CaptainPanic, on 3 October 2011 - 01:39 PM, said:

It seems to me therefore that the only place that you can reliably measure the force applied is just above the broad part of the paddle.

The force could also be measured with a strain gauge between the seat and the hull.

[Schrödinger's hat]

herbbread, on 3 October 2011 - 04:06 PM, said:

Thanks for the help guys. I'll look a little more into it and see what I can find. If it would require constant calibration, and the measurements weren't that reliable, I'd be more skeptical about any results I actually obtained, and it might not be that useful for what I had in mind. Thanks again.

I was thinking mostly in terms of hard quantitative measurements.
If you're just after something to compare the contribution of different paddlers it might work better.
Also there might be better solutions than the one I was thinking of.
For one the tennis racquets were quite strong and flexed very little. If the paddles flex slightly more the signal will be much larger.