Helium is merely hydrogen's expensive boring cousin.
96 posts • joined 7 Dec 2011
Re: BBC at it again
I've almost given up trying to train media types to actually get facts right - e.g. no it's not "space" no the balloon doesn't explode no it doesn't send the position down via GPS satellites etc etc.
Of the many journos I've dealt with, Lester is one of the small percentage who actually checks his facts.
Good on the school for a) doing it and b) actually recovering the flight. I've seen a few flights lately where people (not schools) completely failed at (b).
We were going to use mine for the LOHAN test flights last summer. It failed horribly before we launched - wouldn't even start up, even with known fully charged battery. It was weeks later when I got it to work again, following a guide on the internet about 20 times till eventually it booted for long enough to load updated firmware. Since then it's been fine, but I can't ever trust it again.
We believe that it actually blew back in the last test in Spain, but the glass wasn't blackened (well not much - just a tad at the underside) so it wasn't obvious. Igniters can short circuit when the blow, plus the battery supply erred on the "let's make sure this goes" side, resulting in an igniter current about 3 times the fuse rating.
So, for next time, "check the damn fuse" gets added to the check list. Also, the SPEARS firmware has been updated to check the fuse and other items so it will report over the radio if there's an issue, and the receiving end will display a "DON'T LAUNCH" message in such a case.
Re: The title is too long.
The camera already draws approx 200mA at 3.3V so it heats itself, so if I were worried (which I'm not) I could just leave the camera on all the time.
I've flown these cameras with very little insulation, and sometimes with none. They've never fogged. It's not a problem and doesn't need a solution.
Re: We assume it has been updated
The problem was actually that the met office didn't launch their normal quota of balloons that day, so the prediction was based on older data than usual. A weather front was predicted to come in during the evening, but actually came in several hours earlier, changing the flight path enormously and thus dooming our heroic playmonaut to an early, salty, wet grave.
Re: smart phone
A reader suggested a Bond-style trigger box, so the RPi was an obvious choice!
The message can't be sent using SMS, but is sent by POSTing a URL to the RockBLOCK server. So yes it could have been done using a simple program on a smartphone or a PC (in fact I tested it all on a PC before porting the code to the Pi).
A foam box landing by parachute at 10mph is going to have trouble killing anyone. Even an American-sized foam box like that one. In the UK our flights are typically much, much smaller.
In the UK there are around 50 amateur flights per year listed on the UKHAS site, and maybe the same again that don't appear there. The UK met office fly about 2000 per year, and they haven't managed to kill anyone either (worst they managed was breaking a greenhouse window).
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The plan was to release the glider before burst, with a tethered line to pull a large 'chute out of the back of the fuselage. The small chute was to help make sure that happened. We had to ensure that the glider fell by parachute and didn't actually fly.
In the end the release mechanism didn't release the glider, so the whole lot came down together. 1.3kg of balloon came down with it to, so the tree-landing was a tad faster than we aimed for. Not that we aimed for a tree either :-)