Updated February 2010
I recently saw this Youtube video:
For those interested in measuring the headspeed of their RC helicopters, I think this method is actually much safer than what I came up with. If nothing else, using the Spectrogram function of Audacity with the IR sensor below will be quicker and easier to read...YMMV. And check the related video links for another by this author that shows you how to calculate the speed of a pass based on a doppler calculation.
The following is a detailed set of instructions to build your own.
These are the parts I purchased:
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The emitter and phototransistor need to be mounted on a handle that will allow you to safely get it close to the blades. I used a damaged rotor. Mark out where the holes for the leads will go, and drill them out. | ||
The components look very similar to LEDs. (And the emitter actually is one.) However, because they are so close together, they'll interfere during operation, so some shielding is needed. | ||
Cover the sides of the emitter and phototransistor with something to block the light produced during operation. I used two small pieces of heat-shrink tubing, but electrical tape would work as well. Be careful not to obscure the round tops of the components. | ||
The emitter and phototransistor can now be placed in the handle. | ||
Time to wire everything up. You'll need a way to attach a AA battery to the circuit. Note that the positve battery terminal is wired to
the long leg of both components. Make sure the wire to the microphone jack is long enough to reach from your work space to your PC or laptop. Tape the wires and battery to the handle and you're done! |
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Although it does far more than we'll need of it, Audacity is free audio editor available for Windows, Mac and Linux. Download and install it, unless you have another piece of software that will do what is needed.
If you found this project interesting, I've also got a instructions for making a paper pitch gauge.
These instructions are distributed under the Creative Commons Attribution-No Derivative
Works 3.0 You may freely distribute and link to it,
but may not change it, claim it as your own, or incorporate it
in other tools.
If you find this tool useful, please consider sending $5 to the author
via PayPal.