At the 1999 International Rocket Weekend (near Largs, Scotland), I built a small microprocessor based data logger/accelerometer. Since it was intended as a small and not too bright computer, I called it FleaBrain2. (It had a predecessor, FleaBrain1, but that's another web page...).
A brief summary:
More details to follow (pictures once I get around to having them developed)...
The test flight used "Mostly Harmless", my Estes Omloid kit. (Since FleaBrain1 ended up in a tree, I was keen to use something that wasn't going to go too far out of range, on a tried and tested rocket).
Using a C6-3 motor, total mass was around 200g at launch. (approx: 85g rocket, 55g payload, 60g motor; motor 10g at burnout).
Some preliminary results
X axis is time in seconds; the 25 second offset is the time between activating the payload and launch. Y axis is accelerometer output (initial pad reading is taken as 1G nominal for processing.) Sample rate was 20ms, or 50 samples per second. (Using 2 bytes per sample, this gives 8000/2 = 4000 samples / 50 = 80 seconds of logging time.)
The ejection charge can be seen firing at x=30, 3sec after burnout as expected. The large negative G spikes are associated with the parachute opening (I suspect the double spike is caused by the shock cord "bouncing" the payload). There follows 17 seconds of descent before landing.
- extracted from the above
Note that with the parachute deployed, the payload section is inverted, hence the -1G reading due to gravity
These graphs were produced using GNUPLOT's postscript driver and converted with GhostView; they are quite small (~4K) but may be a bit unwieldy on smaller window sizes. I intend to regenerate them with better labelling once time permits.
I have made the source code available (under the Perl Artistic Licence).
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