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Okay, so please read my last post if you haven’t already.
Anyway, now that we had a cheap tracking device, we decided to do what any reasonable people would do: send it into near-space. Or, at least, that was the plan.
So our last balloon cost $800. While $800 is pretty cheap considering what we did, we’re all college students, and we haven’t got that sort of money to spend all of the time. Last launch, we spent over $250 on our tracking system (by the way, an excellent device), some $80+ on our balloon, another $80 on helium, $30 on our radar reflector, and $50 on the parachute.
So we decided to replicate a typical launch, but this time to do it as cheaply as we possibly could. We’ve already got a $50 tracking unit (the i290 cell phone uploading data the sensor.network), so now we just need some way to lift it and make sure it lands safely.
In order to do this, we needed a cheap balloon, a parachute, and a radar reflector.
We built the radar reflector out of aluminium foil and foam, sewed the parachute, and found a cheap, 6′ party balloon. $45 for helium at the local Diddams and we were set.
We launched on December 31st, 2009 from just outside of Los Banos, CA. We inflated the balloon with several pounds of lift, and the balloon rose very quickly. At 641 feet, the phone left cellular coverage and began queuing up GPS readings, ready to send them off when back in cellular range, and all we could do was to wait.
We were periodically checking the internet for tracking information, and about an hour later, we began to get readings back from the balloon. We quickly discovered the the balloon had landed after only going to an altitude of around 6,000 feet (more about this later).
We jumped into our cars and drove to the landing site about 30 miles away.
The payload was in perfect condition, and the i290 phone was still on and reporting data just fine.
Now, about the 6,000 feet: it looks like we cheaped out when buying our balloon. There’s still a bit of contention over this, but it looks like a ‘real’ weather balloon has a higher percentage of latex than that of a party balloon. Our party balloon simply was not designed to expand to the same extent as a weather balloon, and burst at 6000 feet. Really, we should have just gotten a weather balloon — it looks like the small ones are just as cheap as the party balloon we bought ($20).
The good news is that we were able to successfully demonstrate that our tracking system worked. I threw together a little webpage that we used to track the thing on the day of the launch. Forgive me, it’s very rough around the edges.
And, if you’re too lazy to click that link, here’s a picture of our GPS trace..
I also threw together a Google Earth KML file of our GPS data; download it here.
All in all, a wonderful time.
Grand total for this project (not including burritos and gas): $145. Not bad.
Tim has also got written about this on his blog.
Oh, and about the code for the phone. I’m not going to release it (at least right now): it’s far too ugly and hackish for me to release to the public. If you email me, I’ll probably send it to you with a long note explaining why it’s no good and you shouldn’t trust it.
So we’ve got these really cool SD cards made by a company called eye-fi. The eye-fi automatically upload pictures to Flickr via wifi.
I’ve also been playing with a CHDK, a hacked version of Canon’s firmware for their point and shoot cameras. CHDK has worked beautifully, allowing me to take pictures in intervals and turn the camera off when it’s not needed (excellent for long deployment on a bridge).
I have, however, had one issue. To get the camera to boot CHDK, the SD card has to be placed in the “lock” position by flipping a switch on the of the card. However, the eye-fi has no such lock. So I’ve had to be a bit creative.
With some help, I cut a slot in the side of the card with a dremel, permanently locking it. No damage to the card was done; it’s still able to save images, etc.
A little piece of tape, placed over the new slot, will unlock the card.