18 June 2012

Balloon-borne camera, part 3 - Stringing the picavet

If you're following from last time, you should now have assembled your picavet cross. Now we need to hang it from the kite line! We do this using a few meters of string and running it through the eyes on the picavet and through some connectors that we will tie on to the kite line (i.e. the keychain carabiners I mentioned in the last post). You'll need to tie some knots - I recommend netknots.com as very helpful.

The process looks like this:

I constantly referred back to this animation while I strung my picavet.

The first thing I did was to cut about 6 armlengths of the string. I had a really frustrating time keeping such a long length from getting hopelessly tangled, so my advice is to hold on to the ends at all times. This should prevent tangles.

I laid out my parts like this:

A short apology - for this version of my picavet, I decided to replace the carabiners with 2 card rings. Since the string goes through each kite line attachment point twice, I thought this might prevent the string from rubbing on itself while in flight. We'll see if there's any difference. Key rings could also work.

You can see that I took one end of the string and tied it to the card rings on the right. This was just to keep it in place while I did the rest of the stringing.

The rubber bands are there in case I decide later to use them to hold the camera - you can't slip them on once the stringing is finished. Rubber bands aren't a very safe way to hold the camera in place, but they are easy to slip on and off the camera if you're doing a lot of testing and the camera isn't going to go very high. I actually found it very helpful to record some footage while just tying the kite line to a coat rack in my office and hanging the picavet and camera from that as I moved the kite line up and down.

Also notice (1) the central washer in the middle of the picavet cross, and (2) all the eyes are facing the same direction!

Using the animation above, I began threading the string. Here are some photos of that.

(1) One end of the string is tied to the card rings.

(2) Hanging on to the loose end, I dumped the string off my desk to free space. The central washer is held down with a heavy magnet as I thread the string through.

(3) Through the first loop of the second set of card rings and back...

(4) Through the right eye...

(5) Through the left eye!

When you've gone through the last eye, hold the free end of the string while untying the other end. I used a double fisherman's knot. Then, tie the ends together and cut off excess string. You're done!

It definitely took me a couple tries to get it right. The more I tried, the easier it was to understand how the picavet is supposed to be strung. Even if my instructions and pictures aren't very clear, really the best way to string the picavet correctly is just to try it a couple times until the method begins to make sense.

Here is the final product!

The next post will be short and sweet, about connecting the picavet to the kite line.


Rebecca said...

This is cool Jonathan! I wish I had an interesting science question I could ask you that you demonstrates how much I know about natural gases and other science-y things, but I can tell you that the reason that the U.S. is trying to sell all of its reserve off by 2015 is to open up the federally controlled price of helium to the market. The U.S. government actually currently controls/has in reserve 1/3 of the world's supply of helium, which is immense. In the U.S. there's been a "shortage" but that's probably because most places don't want to keep buying helium supplies now when they know the price is going to go down in two years. The U.S. should be keeping a small reserve though for research, although there's not much information about how it will be managed.

Larus Aquarium said...

Thank you so much for posting the threading animation. I was able to follow your directions and for less than $5 I was able to make my own KAP picavet.