highaltitude.log.20080817

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[00:34] <fuzzylugnuts> wooo
[00:35] <fuzzylugnuts> http://www.savinglots.com/lotprod.asp?item=ULCRP2
[00:35] <fuzzylugnuts> it says 3 and 6 volts
[00:35] <fuzzylugnuts> 1600mAh
[00:35] <fuzzylugnuts> two in parallel, at 6v
[00:36] <fuzzylugnuts> and only 18g each
[00:36] <fuzzylugnuts> *finally* found a freeking battery to use.
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[11:56] <robert1971> jcoxon: Do you get your helium from the university? Or do you order it? I'm thinking of getting 4m^3 from BOC
[11:57] <jcoxon> robert1971, as i'm not at Cambridge anymore i don't get helium provided
[11:57] <jcoxon> rocketboy has a supplier thats a bit cheaper
[11:58] <robert1971> Do you use BOC?
[11:58] <jcoxon> its a local party supplier
[11:59] <robert1971> Getting my kit together for a teathered launch in the next couple of weeks.
[12:00] <jcoxon> oh excellent
[12:01] <jcoxon> i need to put in some work this week in preparation for next weekend
[12:16] <robert1971> Good luck with the weather.
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[12:43] <robert1971> Finished the final touches to the IXUS hacking guide
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[16:23] <mc-> fergusnoble, was reading the logs on film tensioning
[16:34] <mc-> the rig we saw at aelson measured tension and adjusted the motor speed, IIRC
[16:35] <SpeedEvil> Yeah - that's the easy way. Measure film sag, or use a roller on a spring.
[16:35] <SpeedEvil> You want some slack in the system anyway typically.
[16:35] <SpeedEvil> Otherwise you risk minor misalignments causing major tensions.
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[17:04] <fergusnoble> mc-: the difference is he was using a conveyor belt to move thr bulk of the material i think
[17:05] <fergusnoble> i guess its still the same for the tensioning though
[17:07] <mc-> I must have missed the conveyor belt part...
[17:08] <mc-> was the belt so that the film moved at a constant speed?
[17:08] <fergusnoble> i think just to take the sheer weight of it
[17:09] <fergusnoble> so it didnt sag in the middle
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[17:13] <mc-> are you thinking of using a belt or just drag it across a table ?
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[17:18] Action: SpeedEvil finds a roll of plastic in the attic.
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[17:29] <fergusnoble> mc-: was hoping just to drag it
[17:30] <fergusnoble> if that doesnt work out will add a belt
[17:30] <jcoxon> afternoon all
[17:42] <mc-> jcoxon
[17:42] <mc-> was thinking about trying to make a long duration balloon without ballast
[17:43] <jcoxon> mc-, right
[17:43] <jcoxon> zero pressure?
[17:43] <mc-> yes, but it floats at a high altitude during the day
[17:43] <mc-> and lower at night
[17:43] <jcoxon> yup
[17:43] <mc-> would that work?
[17:44] <jcoxon> thats how a zp works
[17:44] <jcoxon> but when it rises it'll vent helium
[17:44] <jcoxon> so that at night it'll descend further
[17:44] <mc-> but a zp vents
[17:44] <jcoxon> so a superpressure then
[17:44] <mc-> how about a zp that is underfilled?
[17:44] <jcoxon> a zp will rise till it vents
[17:44] <mc-> so when it expands during the day it never vents
[17:45] <jcoxon> (unless there isn't enough helium to keep it up)
[17:45] <jcoxon> a zp will rise till it vents sufficiently to be at equlibrium and floats
[17:45] <mc-> does a zp has an altitude it would float at? given a fixed volume of He
[17:46] <jcoxon> yeah, it'll rise till its has vented helium so its lifting force equals the downward pull
[17:46] <jcoxon> so you could work it out
[17:46] <mc-> or can a zp be vented and then the vent is closed once it's floating?
[17:47] <SpeedEvil> yes.
[17:47] <jcoxon> yeah
[17:47] <jcoxon> but when night comes it'll descend
[17:47] <SpeedEvil> Though it will rise and fall a bit due to night/day
[17:47] <jcoxon> and each day it'll get lower
[17:47] <mc-> then it wouldn't lose any more He, so it could float for a long time?
[17:47] <SpeedEvil> mc-: diffusion is a problem
[17:47] <SpeedEvil> I suspect.
[17:47] <jcoxon> hence the need for ballast
[17:48] <mc-> I thought the ballast was needed because at night, it vents more He ?
[17:48] <SpeedEvil> I suppose if you make it reflective, the night/day difference will be smaller.
[17:48] <mc-> if the vent was closed, there will be a slight loss of He from diffusion
[17:48] <jcoxon> mc-, no at night it cools therefore it doesn't remain expanded
[17:48] <jcoxon> so you don't vent
[17:49] <mc-> the US long duration balloons seem to need a lot of ballast
[17:49] <mc-> if there was thicker plastic, the diffusion would be less
[17:49] <jcoxon> but it would be heavier
[17:50] <SpeedEvil> I don't know if metallised mylar would have significantly lower diffusion due to the metal layer.
[17:50] <mc-> overall it would be a win, because less surface area as no ballast would be required if the vent is closed.
[17:51] <mc-> from memory, the SNOX was 80%+ ballast
[17:51] <jcoxon> in theory it should work
[17:51] <jcoxon> but the ballast certainly helps
[17:51] <jcoxon> your issue is the finite He
[17:52] Action: SpeedEvil wonders on light H generators that don't melt.
[17:52] <mc-> if the payload was really light, then it wouldn't matter is He was lost, since it would float very high.
[17:52] <jcoxon> oh it would float for a longtime
[17:52] <mc-> and gradually descend
[17:53] <SpeedEvil> ballast is more important if you care about where it floats AIUI.
[17:53] <jcoxon> yeah
[17:53] <SpeedEvil> If you just care about 'up tehre' it's not really that much of a problem.
[17:53] <jcoxon> it would not be popular once it begun to descend
[17:53] <SpeedEvil> Or if you want to extend the flight time lots.
[17:53] <mc-> I think SNOX didn't use ballast to control float altitude
[17:53] <mc-> they used it to keep it in the air longer
[17:54] <jcoxon> yeah
[17:54] <jcoxon> they used it to get higher after the decesent at night
[17:54] <SpeedEvil> Once it starts to descend (over what the diurnal variations are) you drop ballast.
[17:54] <SpeedEvil> To make up for diffusion and leaks.
[17:55] <SpeedEvil> I suspect a H2 generator would be very hard at altitude.
[17:55] <mc-> if there's no ballast, then it would go really high during the day.
[17:55] <SpeedEvil> At least a simple Al/Lye ones.
[17:55] <SpeedEvil> As the lye will freeze.
[17:56] <SpeedEvil> (assuming something like a container on a PTFE pipe, that will freeze out the water on the walls leading to the balloon.)
[17:56] <jcoxon> mc-, it would go high
[17:57] <jcoxon> but i doubt it will last as long
[17:58] Action: SpeedEvil wonders how much H2 is in an AA HiMH cell.
[17:58] <mc-> Could a large latex survive if it was underfilled with a lightweight payload (50gms)?
[17:58] <SpeedEvil> mc-: sure - if you get teh fill right
[17:58] <mc-> it might need a lift balloon to get it to float altitude
[17:58] <jcoxon> but won't it just burst
[17:59] <jcoxon> oh right
[17:59] <jcoxon> yeah if you did a neutral lift balloon
[17:59] <jcoxon> and a lift balloon
[17:59] <mc-> does a latex degrade in UV light?
[17:59] <jcoxon> then it would be a matter of diffusion
[17:59] <jcoxon> yes
[17:59] <SpeedEvil> Launch it at night.
[17:59] <mc-> good idea
[18:00] <jcoxon> that would give you more time
[18:00] <jcoxon> but thats also the problem
[18:00] <jcoxon> a neutral density balloon at night will rise during hte day
[18:00] <jcoxon> netural lift*
[18:01] <mc-> how about a lift balloon which stays on during the night, and 'pops' the next day?
[18:02] <jcoxon> mc-, so a very gradual ascent? then it reaches its burst altitude and the payload is left with a neutral lift balloon
[18:02] <mc-> yes, seems possible to me.
[18:02] <SpeedEvil> Or you just vent.
[18:03] <SpeedEvil> GPS controlled.
[18:03] <jcoxon> it might be easier to vent
[18:03] <jcoxon> or use ballast
[18:03] <SpeedEvil> That of course leaves you with the valve problem.
[18:03] <SpeedEvil> Bags of sand, and a winch servo is damn simple.
[18:04] <mc-> ballast adds weight, and increases size of balloon.
[18:04] <SpeedEvil> Yep.
[18:04] <jcoxon> indeed but its a lot easier then latex
[18:04] <SpeedEvil> How much do balloons 'really' cost?
[18:04] <mc-> trying to work out how long a non-ballasted ballon could last
[18:04] <jcoxon> to get a latex balloon to be neutrally bouyant at alt
[18:04] <SpeedEvil> I notice they are on ebay occasionally.
[18:05] <jcoxon> oh Mark Caziell can supply them
[18:05] <SpeedEvil> mc-: the other problem is comms to out over the atlantic (say)
[18:05] <mc-> I've got a satellite modem that weighs a few grams
[18:06] <SpeedEvil> Oooh.
[18:06] <SpeedEvil> sat-phone?
[18:06] <jcoxon> and you could use powerful radios
[18:06] <mc-> a data module
[18:06] <mc-> also have a 10.14MHz transmitter in the ham bands
[18:06] <SpeedEvil> wifi to passing airliners :)
[18:07] <mc-> weighs ~20grams
[18:08] <jcoxon> ballast does bring some flexibility to the flight
[18:08] <mc-> agreed
[18:12] <jcoxon> mc-, you thinking about a transatlantic flight then?
[18:13] <mc-> that would be really good, I've got all the electronic bits needed
[18:16] <jcoxon> USA -> UK?
[18:17] <mc-> yes, or else just practise by sending stuff across Europe?
[18:17] <jcoxon> natrium is certainly interested in something
[18:17] <jcoxon> from Canada across
[18:17] <jcoxon> across europe would worry me a little
[18:18] <jcoxon> but then i do overly worry
[18:18] <mc-> perhaps better then to start from the US
[18:19] <jcoxon> perhaps
[18:21] <mc-> natrium needs to get his ham license... :)
[18:21] <jcoxon> details :-D
[18:21] <jcoxon> so do I!
[18:22] <mc-> or find someone who has a license
[18:23] <mc-> canada seems a good place to start, since it's not so far across the Atlantic
[18:24] <mc-> newfoundland would be best
[18:25] <mc-> bbl
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[18:29] <jcoxon> hey edmoore
[18:29] <edmoore> ello
[18:29] <edmoore> how's tricks?
[18:29] <jcoxon> good thanks
[18:29] <jcoxon> had a good weekend
[18:29] <jcoxon> people to stay
[18:30] <jcoxon> just playing with my canon a60, got remote capture working on my mac
[18:30] <jcoxon> next to do it on the gumstix
[18:36] <edmoore> wicked awesome
[18:37] <jcoxon> how about you?
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[18:42] <edmoore> knackered. out to Reading last night, then trashed at squash this morning
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[19:33] <natrium42> hi
[19:33] <icez> hi
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[20:56] <mc-> lots of ppl, but nobody is saying anything?
[20:59] <phatmonkey> suppose not.
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[21:01] <Laurenceb> hi everyone
[21:04] <natrium42> hey
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[21:10] <natrium42> hi akawaka
[21:10] <akawaka> yo
[21:11] <natrium42> i am in san francisco atm :)
[21:12] <akawaka> BayATM
[21:12] <akawaka> what yah doing there?
[21:12] <natrium42> yah, stanford
[21:12] <natrium42> tourism
[21:13] <akawaka> i like san fran
[21:13] <natrium42> visiting my sister who took stanford summer program
[21:13] <natrium42> the nature is nice
[21:13] <akawaka> yeah, stanford is really cool
[21:14] <Laurenceb> nature?!
[21:14] <akawaka> i like how if you look at san francisco from a high point it kind of looks like the city is built into the landscape
[21:14] <akawaka> little hills and parks jutting out all over the place
[21:15] <akawaka> go up to twin peaks if you get a chance
[21:15] <akawaka> its got the best view of the cityt
[21:16] <natrium42> ah, cool
[21:17] <jcoxon> natrium42, got the camera
[21:17] <natrium42> i may also go tandem paragliding
[21:17] <natrium42> jcoxon, so they sent it to the right address after all?
[21:17] <jcoxon> yeah
[21:17] <natrium42> neat-oh
[21:17] <jcoxon> its pretty heavy so i'm stripping it down
[21:17] <natrium42> have you tried controlling it from the verdex yet?
[21:18] <jcoxon> got it working on my laptop
[21:18] <jcoxon> and have compiled capture for the verdex
[21:18] <natrium42> k
[21:18] <jcoxon> will upload it tomorrow
[21:18] <natrium42> the ptpcam program is also good to crosscompile
[21:18] <natrium42> it allows to reset the camera
[21:18] <natrium42> ptpcam --reset
[21:19] <jcoxon> okay cool
[21:20] <natrium42> oh, and make sure you stress test the capturing
[21:20] <natrium42> some older cameras had a thing where you had to restart it each 200 shots or so
[21:20] <jcoxon> might be worth resetting regularly?
[21:20] <natrium42> yeah
[21:23] <mc-> hey natrium, got the serial logger, thanks.
[21:23] <natrium42> mc-, sure, np
[21:24] <natrium42> jcoxon, does sstv require ratio of 320:256?
[21:24] <jcoxon> thats the standard
[21:24] <natrium42> cameras use ratio of 320:240
[21:24] <jcoxon> i know
[21:25] <natrium42> you're going to crop it?
[21:25] <jcoxon> i've got netpbm to add a border
[21:25] <jcoxon> to make it up to 320 x 256
[21:25] Action: natrium42 would crop :P
[21:25] <natrium42> since res is already small
[21:25] <natrium42> why waste it on border
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[21:26] <jcoxon> its more i put 16 more lines at the top (which is at risk of being lost if we are slow at setting up the receving program)
[21:26] <akawaka> you could put some extra info in the border
[21:27] <akawaka> netpbm would be able to add some text in there for you
[21:27] <akawaka> some color bars for calibration maybe too
[21:27] <jcoxon> once i've got it all working i'll have a play
[21:28] <natrium42> MORE FEATURES PLZ
[21:28] <natrium42> :D
[21:28] <akawaka> sell ad space in the border
[21:28] <natrium42> 1 pixel = $1 ?
[21:28] <akawaka> what kind of radio are you using for the sstv?
[21:29] <jcoxon> to transmit?
[21:29] <jcoxon> radiometrix attached to the audio out of the gumstix
[21:29] <akawaka> yeah
[21:29] <akawaka> 10mw?
[21:29] <jcoxon> ntx2
[21:29] <natrium42> akawaka, it's on his page :P
[21:29] <jcoxon> yup
[21:29] <akawaka> url?
[21:30] <natrium42> http://www.pegasushabproject.org.uk/wiki/doku.php/missions:haps:haps-1
[21:33] <akawaka> love it
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[21:34] <akawaka> its the perfect open source balloon project, cobbled together from a hundred different pieces
[21:34] <jcoxon> its coming together rather well
[21:34] <jcoxon> right i've got this camera down to 190g from 275g
[21:39] <natrium42> excellent
[21:39] <jcoxon> 170g now
[21:39] <natrium42> so there is also doug's camera?
[21:39] <jcoxon> yeah
[21:39] <jcoxon> powershot a560
[21:39] <jcoxon> doing stills and also video
[21:40] <natrium42> :)
[21:40] <natrium42> if only half of the stuff works, it's going to be still a very impressive mission
[21:40] <jcoxon> got to build the backup beacon
[21:40] <jcoxon> got a different freq radio module
[21:51] <jcoxon> right i think i've reached the limit: 160g
[21:53] <jcoxon> bbiab
[21:55] Action: SpeedEvil passes jcoxon a lens whittled from lime jello.
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[23:46] <Laurenceb> anyone here have any experience with embedded kalman filters?
[23:46] <Laurenceb> I've got the kalman filter up and running on the parafoil board, but theres a few weird problems
[23:47] <Laurenceb> it seems to stabilise correctly with the gyro stationary, but if you move it too fast it goes mad
[00:00] --- Mon Aug 18 2008