[aprssig] USNA Party Balloon Success!
scott at opentrac.org
Sun Apr 29 19:24:43 CDT 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:
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
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.
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