28 June 2012

Balloon-borne camera, part 5: balloon choice, and first flight!

We've connected the picavet to the line, so now we're ready to fly! Now we need balloons. How many, though?

(Apologies in advance for the lack of pictures at the beginning of this post, there will be awesome pictures and video later)

Well, I did some quick measurements to make an initial guess. Our camera masses about 30 grams, and so does our picavet rig. This means the balloons need to lift 60 g plus the weight of the line itself. I filled four standard 12"-diameter party balloons with helium and strapped them to a spring scale (GIS for spring scale) to find out how much mass they could lift. Four balloons lifted about 10 g, or 2.5 g per balloon. (Using more balloons will get you a better estimate of the average, but we didn't really need to be precise).

According to this measurement, we need a minimum of 24 balloons to get off the ground. I rounded up to 30 to take into account the kite line and winds, which (unlike for kites!) seem to keep the balloons down.

Filling up 30 balloons is a huge pain! My fingers were red and aching after tying them all, even with help from Melanie and Christina here at the museum.  I found it very helpful to cut 30 long (3-6 feet) strings ahead of time, and tied a slip-knot into each end. I brought a carabiner with me, hooked it onto a convenient place near the helium tank, and put one end of each string around the carabiner. Whenever I finished filling and tying a balloon, I just grabbed the next available string, looped the loose end around the knot in the balloon, and pulled the string tight. Then, when I let go of the balloon, it didn't float away!

Also, a quick word of warning if you're doing this at home - be super careful with compressed gas tanks. Make sure they are properly secured, because they can be really dangerous.

With 30 balloons attached to a carabiner attached to my belt loop so I could carry the camera rig and other equipment in my hands, I went outside to see how it worked!

Here's the setup still attached to the cart while I took some pictures. Left to right, you can see the ton of balloons tied to an orange carabiner by a mass of black strings. Then comes the kit line, the picavet, and finally the cart o'stuff which I think had scissors, tape, my notebook, and other miscellania that I might need. You can tell there was some wind going on that day.
Up, up, and away!
Picture taken from day 2 of testing, with more balloons. See those power lines in the background? They were far away (further than the amount of line we had, anyway) but it still would have been nice to pick a more open space.

It was super cool to see all the hard work finally come together! We have some video from the camera, which I will post later once I get it from the computer where it currently lives.

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