Calculating Speed with an accelerometer

OK now we're thinking outside the box!

I like the microphone idea. I'll just add onto it if I may. The RC car will have a certain pitch at different velocities...so why not just FFT (and filter) the sound of the car to determine velocities. Even when the batteries start to die, the sound of the gears will remain constant based on any given velocity.

You could use just a pick-up mic to listen to the car, or for extended range, use a cheap wireless mic.

Thomas

Yes it is well measured, but that is mainly because it varies from place to place. If it didn't, people wouldn't still be measuring it.

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kensmith@rahul.net   forging knowledge

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Both

OK, well, that is interesting, but if you were trying to convince me that the LDRS uses local oscillators on their rockets, then detects Doppler shift from the ground, you haven't exactly succeeded. I will have to reserve judgement. ;-)

--Mac

in

shifted due

shift. Both

I'm not trying to convince you of anything. Just reporting what I saw. I tried locating the info and could not. The info is worth every penny you paid for it ;)

Jim

What could work is transmit some frequency to the ehicle, double or triple it in frequency there and radiate it back.

This should give a nice phase difference to measure. Multiple receivers on the ground can obviously use the same reference signal.

If interference is not a problem somehow and range is limited the frequency tripler can be rather simple and even passive.

Thomas

Jumping in rather late in the thread...

If I remember correctly (and I'm sure I do), the rocket velocities and peak altitude were measured by a radio telemetry unit, probably an R-DAS

The problem with using a flying transmitter and ground-based receivers to mesure the doppler shift is that the shift is so small for practical transmitter frequencies and the velocities the rockets travel at. The R- DAS used barometric pressure and accelleration for its measurements.

On a similar note, it was just about 11 years ago when I presented a poster at AAHPERD* on the use of accellerometers in measuring human performance. Until then no one had come up with a way of continuously measuring power output, especially instatanious power and power/distance ratio. We hooked up accelerometers to different types of stationary exercise equipment (leg press, Smith machine, etc) and logged the data into a computer. We only recorded the accelleration over time, and post run calculated power, velocity, distance, etc, using Excel.

*AAHPERD=American Association of Health, Physical Education, Recreation, and Dance.