Measuring Acceleration/Speed for Small Vehicles?

stampfli_brit asks: "I am the captain of rowing at my local club, and was looking for a way to improve training. We have an NK SpeedCoach. However, I was looking for something that could measure the speed of the shell several times a second, more like this [pdf]. Any ideas on a cheap system using IC accelerometers or GPS, that could get this kind of information, log it for an hour or two, then dump it to an Apple Mac for analysis?"

Comments

Oh, that's easy!

[NewWazoo]

All you need is a string, a weight, three poles, and a protractor.

Make a crossbar out of the poles, and mount the protractor to it, with 90* facing downward. Tie the weight to the string, and hang the lot right next to the protractor. Align the contraption such that the length of the protractor runs parallel with the keel of the boat.

With some (very) simple fizzix, you've just built an accelerometer.

B

Re:So which is it?

[confusion here]

Actually you can't. Acceleration is a vector and speed is a scalar. Speed is the magnitude of velocity. Additionally, the derivative of speed is not the magnitude of acceleration, but rather the magnitude of the tangential component of acceleration.

/nitpick ;)

Ball bearing solution

[stick_figure_of_doom]

My crew club is having another problem (which I know all crews are subjected to). The steel ballbearings in the slide wheels rust out, and when you have 4 wheels for 8 seats you have 32 wheels rusting. We end up replacing the shotty we find about every two weeks. The old slide solution didn't involve ballbearings, but it sucked. It involved rolling axles attached to the wheels, a sliding plate, and another set of rollers below the actual seat. It jams all the time, but it never rusted out. What would anyone say is a more appropriate mechanical solution? Thanks for not modding this off-topic, because you don't see crew on /. very often...