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[aprssig] USNA Party Balloon Success!

Scott Miller scott at opentrac.org
Mon Apr 30 00:24:43 UTC 2012


> It is clever I think.  Pictures next week...  a 10 ohm 1/8th watt carbon film resistor makes an excellent REUSEABLE burn device for fishing line on about 6 to 8 volts.  But to this I added a little two-pin header socket in series.  One string is tied to the resistor which burns it for release, but a second string is tied to a U shaped jumper in the 2 pin socket.  When the first string is released, then all the load is on the second string and the jumper which is pulled from the socket.

That's exactly the scheme I came up with several years ago.  Here's my 
original implementation, ca 2006:

http://n1vg.net/images/cutdown.jpg
http://n1vg.net/images/cutdown-detail.jpg

The top and bottom resistors are only there to keep the string in place. 
  They were later replaced by holes in the PCB.

It's shown here with 200+ lb test Spectra (UHMWPE) cord tied in a clove 
hitch.  I later set it up so that it looped through rings several times 
such that only a fraction of the weight was on the resistor.  It held my 
weight and cut successfully with a 9v battery.  I was using a metal film 
resistor.

I've since integrated this system into a couple of single-board payloads 
but haven't yet used it in flight.

Nylon also seems to work, but Spectra has a good combination of low 
melting point and high strength, and since you only need a little bit of 
it the cost is inconsequential.

Scott
N1VG



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