highaltitude.log.20080205

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[16:30] <Laurenceb> hi all
[16:30] <Laurenceb> grrr this radio isnt working
[16:31] <Laurenceb> the truetty trace is very dodgy
[16:31] <Laurenceb> I'm using the mic socket
[16:31] <Laurenceb> maybe why?
[16:31] <Laurenceb> it looks like interharmonic distortion
[16:31] <Laurenceb> I'm getting a good signal on the icom rx
[16:32] <Laurenceb> edmoore: have you used truetty?
[16:32] <edmoore> yes
[16:32] <edmoore> but not for a while
[16:32] <edmoore> and recall very little
[16:33] <Laurenceb> the discriminator trace is really bad
[16:33] <Laurenceb> but my signal sounds good
[16:33] <Laurenceb> I suspect distortion in my sound card
[16:35] <Laurenceb> ant works well
[16:35] <Laurenceb> saturates the rx
[16:38] <Laurenceb> hmm I have sub peaks on the fft
[16:39] <Laurenceb> interharmonic distortion for sure
[16:39] <Laurenceb> :(
[16:39] <Laurenceb> its either the icom radio or my sound card
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[17:11] <jatkins> hi all
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[17:38] <jatkins> hi jcoxon
[17:39] <jatkins> I've been thinking of a method of cutdown involving electromagnets
[17:39] <jatkins> http://wiki.ukhas.org.uk/projects:habep:magnetic_cutdown
[17:39] <jatkins> I've g2g now but if you could have a look at it and see it it's feasible I'd really appreciate it
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[17:47] <Hiena> Good evening!
[17:49] <jcoxon> hey Hiena
[17:50] <Hiena> Ho! How is going?
[17:50] <jcoxon> not bad thanks
[17:50] <jcoxon> you?
[18:05] <Hiena> Tired. trying to schedule my pal next C lecture, the aluminium casting, my part time job, my girlfriend, and the water meter reading on this week. Not to mention the train workers strike...
[18:06] <jcoxon> urgh, not that fun then
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[18:06] <jcoxon> i'm doing admin
[18:06] <jcoxon> stuff i should have done weeks ago
[18:07] <Hiena> Admin what?
[18:07] <jcoxon> oh bills and things
[18:12] <jcoxon> hey jatkins
[18:12] <jatkins> hi
[18:12] <jcoxon> so walk me through this cutdown
[18:13] <jatkins> so during ascent, the permanent magnets are on either side of the ropes
[18:13] <jatkins> and they are within a container
[18:14] <jatkins> both the magnets and the rope put together are thicker than the hole through which they enter the container
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[18:15] <jatkins> and there are metal discs thicker than the rope attached to the bottom of the ropes. so the payload stays attached
[18:15] <jcoxon> okay
[18:15] <jatkins> until you pull away the permanent magnets
[18:16] <jcoxon> so they seperate and move to the electromagnets
[18:16] <jatkins> yep
[18:16] <jcoxon> releasing the string which will now fit through the gap at the top
[18:16] <jatkins> yeah
[18:16] <edmoore> looks like I've walked in on a good idea being formed
[18:16] <jcoxon> http://wiki.ukhas.org.uk/projects:habep:magnetic_cutdown
[18:16] <jatkins> :)
[18:17] <jatkins> ..not sure how it would fare in high wind though
[18:18] <edmoore> i reckon that'd hold up pretty well. And it's nice and clean, too.
[18:18] <edmoore> Good thinking josh
[18:18] <jatkins> thanks
[18:18] <jcoxon> perhaps suspend the magnets on elastic or something
[18:18] <jcoxon> to guide their movement away
[18:18] <jatkins> ok
[18:19] <jatkins> i'll try and prototype it
[18:19] <jcoxon> so does the attraction between the magnets on the rope hold them in place
[18:19] <jatkins> yeah
[18:19] <jcoxon> till the electromagnet turns on and is stronger so pulls them apart
[18:19] <jatkins> yep
[18:20] <jatkins> not sure how much power it would need
[18:20] <jcoxon> yeah
[18:20] <jatkins> the coils on the electromagnets would need to be wired to the flight computer
[18:20] <jcoxon> well through a FET
[18:20] <jcoxon> but yeah
[18:21] <jatkins> ok
[18:21] <jatkins> perhaps use gpios to activate an external power source?
[18:21] <jatkins> i.e. battery
[18:21] <jcoxon> yeah, thats pretty much the plan, the FET would act as a switch and would be triggered by the gpio
[18:22] <jatkins> oh right, ok
[18:22] <jcoxon> you wouldn't need too much power, just enough to shift the magnets, i like the way that you don't need it on all flight
[18:22] <jatkins> i'll look them up, not heard of FETs before
[18:22] <jatkins> ok
[18:23] <jatkins> obviously it depends on the strength of the permanent magnets
[18:24] <jcoxon> you could probably do it with a single magnet and an electromagnet
[18:24] <jcoxon> have the single magnet attached to say a metal plate
[18:25] <jcoxon> and use the electromagnet to pull it away
[18:25] <jcoxon> i'm worried that with 2 electromagnets actually you might not seperate them but instead swing the whole thing to one side
[18:25] <jcoxon> if the balance isn't perfect
[18:27] <jatkins> oh right
[18:27] <jatkins> that's even better though - less power
[18:27] <jcoxon> or
[18:27] <jcoxon> how about this
[18:28] <jcoxon> so we have an electromagnet with a metal core
[18:28] <jatkins> k
[18:28] <jatkins> ok*
[18:28] <jcoxon> and we attach the magnet to that, sandwiching the rope in between
[18:28] <jcoxon> then we turn the electromagnet on but orientate it to it repels the magnet
[18:29] <jcoxon> so it repels*
[18:29] <jcoxon> releasing the string
[18:29] <jatkins> that sounds great
[18:29] <jatkins> didn't know electromagnets could repel?
[18:29] <jcoxon> hmmm i better check that
[18:29] <jcoxon> edmoore,
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[18:30] <jcoxon> jatkins, yeah they will as they generate a magnetic field
[18:30] <jcoxon> and so will have a 'N' and 'S'
[18:30] <jatkins> oh right ok
[18:31] <jcoxon> would need to run some experiments
[18:31] <jcoxon> shouldn't be difficult!
[18:31] <jatkins> yeah
[18:31] <jatkins> coil + core + battery + permanent magnet :)
[18:31] <jcoxon> but excellent idea
[18:32] <jcoxon> and a bit of string
[18:32] <jatkins> thanks
[18:32] <jatkins> yeah
[18:33] <jatkins> would having just one electromagnet require it to be turned on for the whole flight?
[18:33] <jatkins> or just kept there by the permanent magnet..
[18:34] <jatkins> sorry, my mistake
[18:35] <jcoxon> nah the permentnt magnet would do that
[18:35] Action: jcoxon is looking for a magnet
[18:43] <jatkins> I've created a new diagram and revised the description (I've moved the page) http://wiki.ukhas.org.uk/ideas:magnetic_cutdown
[18:44] <jcoxon> yup looks good
[18:44] <jcoxon> still can't find a magnet
[18:44] <jatkins> ok
[18:44] <Hiena> How about the common pin pulling lock?
[18:45] <jatkins> hadn't thought of that ... probably easier
[18:45] <jatkins> anyway, g2g
[18:45] <jatkins> cya jcoxon, Hiena
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[18:46] <jcoxon> as long as the pulling pin didn't get any moisture on it :-D
[18:48] <natrium42> interesting
[18:48] <Hiena> Nah, if you make it loose, and use a small piece rare earth magnet, it will works.
[18:48] <jcoxon> even if it freezes?
[18:49] <natrium42> not sure i would risk it though
[18:49] <jcoxon> i don't like things that go bang
[18:49] <natrium42> it's also possible to use a servo and a similar ring chain as in a human parachute
[18:49] <jcoxon> i lost hearing for a couple of hours at the launch of peg V as the cutdown went off too early
[18:49] <jcoxon> servos will freeze
[18:49] <natrium42> yah, exactly
[18:49] <natrium42> also risky
[18:50] <natrium42> though the tilt servo on my flights did not freeze :P
[18:50] <Hiena> jcoxon, it's simple. Buy a half kg dry ice and test it.
[18:50] <jcoxon> yeah
[18:50] <jcoxon> i shall do
[18:50] <jcoxon> when i find a magnet :-p
[18:50] <natrium42> jcoxon, have you ever tried a mechanism to cut away a *burst* balloon before it tangles with the chute?
[18:51] <jcoxon> no, but its certainly been thought about
[18:51] <jcoxon> also we thought of adding a bit of polystyrene to act as an air brake to keep the balloon away from the parachute as it decends
[18:52] <natrium42> that might work
[18:53] <natrium42> i might try a pressure sensor inside the balloon
[18:53] <natrium42> pressures should be different, right?
[18:53] <natrium42> because it's not a zero pressure balloon
[18:53] <jcoxon> yup
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[23:12] <Quai> you could check the force applied on the cord. It should be much less after the ballon has bursted
[23:14] <Quai> but, might be triggerd by turbulence
[23:30] <natrium42> yes, that's the concern
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[00:00] --- Wed Feb 6 2008