highaltitude.log.20070206

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[09:28] <jcoxon> hey defy
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[11:44] <Golfgeo> Hi all
[11:50] Nick change: Golfgeo -> Golfgeo|School
[11:51] <Golfgeo|School> Reading the UTARC "Compendium" and it is very handy :-)
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[16:07] <jcoxon> hey hmh33
[16:09] <hmh33> hi James
[16:09] <hmh33> Ed and I are going to have a chat this evening around 6:30, Carl might be there, you're welcome to come as well if you like
[16:10] <jcoxon> in engineering?
[16:12] <hmh33> probably in Churchill
[16:12] <jcoxon> oh right
[16:12] <jcoxon> i'm going to the cinema leaving catz at 7.10
[16:13] <hmh33> ok, not to worry then
[16:13] <hmh33> RAG blind date? ;)
[16:13] <jcoxon> nah - anti blind date - lots of us
[16:13] <jcoxon> would like to come but can't
[16:14] <hmh33> nice move
[16:14] <jcoxon> would be an interesting talk
[16:14] Action: hmh33 grumbles
[16:14] <hmh33> my blind date bailed on me
[16:14] <jcoxon> oh no
[16:14] <jcoxon> right i've got to dash
[16:14] <hmh33> pah, philosophy students
[16:14] <jcoxon> bbl
[16:14] <hmh33> laters
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[21:28] <hmh33> hi all
[21:28] <hmh33> Steve, what do you think of this radio? http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=330084726095
[21:29] <hmh33> I know it's not going to be as good as your Yaesu but I thought it might do for testing and as a second station during a flight
[21:29] <rocketboy> hang on I'll take a deco
[21:30] <rocketboy> humm - my connection to ebay is playing up again - I cant download it
[21:31] <rocketboy> ebay seems to go on a go slow every now and again
[21:31] <hmh33> it's an Alinco DJ-X10 wideband scanner
[21:31] <hmh33> does USB and LSB and supports frequency steps of 50Hz
[21:31] <rocketboy> Ah - ok I'll see what i can find
[21:31] <hmh33> it looks similar to the one we were borrowing a while back, and that one did work
[21:32] <hmh33> cheers
[21:36] <rocketboy> actually the scanner of choice is the Yupiteru MVT-7100 for the money - thes usually go for about £150 new on ebay
[21:36] <rocketboy> but the DJ-X10 dosn't seem bad either the sensitivity is fair
[21:37] <rocketboy> how much is it going for?
[21:43] <hmh33> £80 at the moment, ending in 30 mins
[21:43] <hmh33> I thought I'd maybe bid £120 or so
[21:44] <hmh33> apparently it's in "Hardly used" condition, hmm
[21:58] <rocketboy> that seems like a fair price
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[22:09] <hmh33> if a battery has a quoted capacity of 2000mAh and is rated for continuous discharge at 2C does that mean you can safely draw 4A?
[22:12] <hmh33> okay got the receiver for £93
[22:14] <hmh33> plus ripoff P&P of course
[22:15] <rocketboy> ah not bad
[22:17] <rocketboy> As far as mAH is concerned you normally find it is rated at low currents - so if it says 2000mAh you would be unlikly to get that at 4A
[22:19] <hmh33> oh sure
[22:19] <hmh33> but I mean it will supply 4A albeit at a lower capacity? that's what the 2C means?
[22:21] <rocketboy> 2C is the charge rate - 1C would say it should be charged at 2000mA
[22:22] <hmh33> ok
[22:22] <hmh33> well presumably if it can be charged at that rate then it should be able to provide it for a couple of seconds for an igniter
[22:24] <rocketboy> Sure - the current it will supply in short periods is determined by the internal resistance rather than anything else
[22:25] <rocketboy> are we taliking Ni-Cads NiMh li-po?
[22:25] <hmh33> LiPo
[22:25] Action: hmh33 tests
[22:26] <hmh33> ok well it just blew the 10A fuse on my meter so I'm guessing it's good
[22:26] <rocketboy> Ok - they are good for high currents
[22:26] <rocketboy> also they are good for low temps
[22:26] <hmh33> yup
[22:27] <hmh33> I'm assembling a nice use-it-and-forget-it case for Tracker 4
[22:27] <rocketboy> so li-po or li-ion would be the battery of choice for igiters in HABing
[22:28] <rocketboy> Ni-cards (rather than NiMh) are good for normal temp
[22:29] <hmh33> the energy/weight is still significantly worse than disposable lithiums, LiPos are fine for a balloon but I think I'll use one of those photo lithiums for the big rocket
[22:29] <hmh33> they're nice though, and look space-agey
[22:29] <rocketboy> I normally fire the igniterts off a capacitor
[22:30] <hmh33> oh, interesting
[22:30] <hmh33> camera flash?
[22:30] <rocketboy> They normally fire off 2000uF at 5V
[22:30] <hmh33> ok
[22:31] <hmh33> how much reliability margin is there with that?
[22:31] <rocketboy> its all about energy - the more sensitive ones go in 20mS at 1.6A
[22:31] <hmh33> that's pretty fast
[22:31] <rocketboy> So that is 320mJ
[22:31] <rocketboy> Cap is 1/2C * V^2
[22:32] <hmh33> yeah
[22:33] <hmh33> I figure I need 5V for both types of GPS we're currently using, so may as well use the same battery for electronics as pyro
[22:33] <rocketboy> The only thing to be aware of is the short during the flare
[22:33] <hmh33> dropping the voltage
[22:33] <rocketboy> when an igniter fires the plasma causes almost a dead short
[22:34] <hmh33> hm
[22:34] <rocketboy> yeah an therefore processor re-set
[22:34] <hmh33> and potentially the leads could end up shorted afterward
[22:34] <hmh33> processor reset isn't a big deal as long as it comes back up
[22:34] <rocketboy> Thats more unlikly - I have never seen that
[22:34] <hmh33> the software pretty much expects it at cutdown
[22:35] <rocketboy> thats why i use the cap
[22:35] <rocketboy> I use a charge pump to get the FET hard on
[22:35] <rocketboy> I was thinking of using a charge pump to get say 15V on the cap
[22:36] <hmh33> that would take a while with a decent capacitance, you might be better off with a teeny transformer
[22:36] <hmh33> although I suppose it can charge for most of the ascent
[22:36] <rocketboy> yep
[22:36] <hmh33> how do the electrolytics handle the temperature?
[22:37] <rocketboy> the main issue is the cap - that gets higher internal resistance with lower temp
[22:37] <rocketboy> actually i think the FETs get better with low temp
[22:37] <hmh33> right
[22:38] <rocketboy> a bank of tantilum caps is better as they handle the low temp better
[22:38] <hmh33> and a lot in parallel would help with the internal resistance anyway
[22:39] <rocketboy> I was thinking of using a RS232 converter (MAX232 etc) to do the charge pump and level conversion to drive a FET
[22:39] <hmh33> should work
[22:39] <rocketboy> they arn't cheap though
[22:39] <hmh33> I've been using the IRF7910 which has a very low threshold voltage
[22:40] <hmh33> MAX232 is free from Maxim...
[22:40] <hmh33> the IRF7910 is a pretty nice chip
[22:40] <rocketboy> sorry I mean the tantilums arn't cheap
[22:40] <rocketboy> Ah OK I wondered
[22:40] <hmh33> 3.3V is enough to turn it on enough to pass at least a few amps, you get two channels in one SO-8
[22:40] <hmh33> ah yeah
[22:42] <rocketboy> those IRF7910 are good
[22:47] <rocketboy> where do you get them from?
[22:49] <hmh33> that's the problem
[22:49] <hmh33> I'm pretty sure it was Farnell
[22:49] <hmh33> but they don't seem to stock them anymore
[22:49] <rocketboy> yeah - I just looked
[22:52] <hmh33> oh no they are there
[22:52] <hmh33> order code 1013366
[22:52] <hmh33> just doesn't come up when you search for IRF7910 for some reason
[22:53] <hmh33> Farnell's website is a bit rubbish
[22:53] <rocketboy> and only 82p
[22:53] <rocketboy> +
[22:53] <rocketboy> ...
[22:54] <hmh33> get 'em while they're hot
[22:54] <hmh33> I'll be putting in an order in the next day or two btw, so let me know if you want some of those or anything else
[22:55] <rocketboy> Ta - can you get me 5
[22:56] <hmh33> will do
[23:01] <rocketboy> The good thing about FETs is they seem to be able to handle much higher pulse currents for the same package size than bi-polars (don't know why)
[23:02] <hmh33> well I thought bipolars always dropped 0.6V or so
[23:02] <hmh33> so there's significant energy dissapated in them
[23:03] <hmh33> though it depends on the pulse length I guess
[23:03] <rocketboy> I think you can get bi-polars to turn on to 0.3 (or even 0.1V) - but you are right Rds on of 0.01 ohm isn't that uncommon
[23:05] <jcoxon> evening all
[23:05] <rocketboy> hiya
[23:06] <rocketboy> I'm still musing over my flight - since the igniter went off the GPS must have been working (it was set to just a cut-down sqaure)
[23:07] <jcoxon> the plot thinkens :-)
[23:07] <rocketboy> so it must be the downlink software that wasn't working
[23:08] <rocketboy> anyway - I need to do some more testing
[23:09] <rocketboy> BTW - how do you get one of those action things to work in IRC?
[23:09] <jcoxon> hehe "/me"
[23:09] <rocketboy> that gets a different colour
[23:09] Action: jcoxon smiles
[23:10] <jcoxon> of course without the quotes
[23:10] Action: rocketboy snots all over the keyboard - i have a cold
[23:10] <jcoxon> bingo
[23:10] Action: rocketboy - i want to die
[23:11] <rocketboy> humm may not be con-incedence
[23:12] Action: rocketboy plys himself with a stiff drink
[23:12] <jcoxon> i'm just getting over my cold
[23:12] Action: jcoxon regrets teaching rocketboy to use "/me" :-)
[23:12] <rocketboy> i'm just going down with it
[23:13] <jcoxon> got an email from the CU Wireless Soc president
[23:13] <jcoxon> confirming that they'd be happy to help at the next launch
[23:14] Action: rocketboy erupts in a mountain of mucus
[23:14] <rocketboy> excellent
[23:14] <jcoxon> they've got a tracking system at their shack
[23:14] <jcoxon> they use it to track satelites but i guess balloons would do the job as well
[23:14] <defy> morning guys
[23:15] <jcoxon> got a azimuth-elevator rotator
[23:15] <jcoxon> hey defy
[23:15] <rocketboy> spiffing - I wonder what kit they have
[23:15] <rocketboy> evening
[23:16] <rocketboy> ah well better get an early night
[23:16] <jcoxon> night rocketboy - hope you feel better soon
[23:16] <rocketboy> c ya
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[23:17] <defy> whens the next planned launch jcoxon?
[23:17] <hmh33> oh hi James
[23:17] <hmh33> and defy
[23:18] <defy> hey
[23:18] <jcoxon> defy, ooo i don't know
[23:18] <jcoxon> the jetstream isn't great
[23:18] <defy> true =/
[23:18] <jcoxon> there are a few windows but not for long
[23:18] <hmh33> I'd like to go for one on the 17th but it will be a lowish altitude flight
[23:18] <hmh33> James, I got the radio
[23:19] <defy> I'm thinking of doing a 1000m moored balloon with my payload, just to test everything out in the real environment
[23:19] <jcoxon> hmh33, cool about the radio
[23:19] <jcoxon> defy, good idea
[23:19] <jcoxon> hmh33, hmmm forecasts look like there could be a window
[23:19] <jcoxon> but of course it might change as we approach it
[23:20] <jcoxon> i'm more of the thinking that we should wait a bit - get over the worst of the winds
[23:21] <hmh33> defy, the CAA probably won't like that
[23:21] <jcoxon> defy ain't in the UK
[23:21] <jcoxon> NZ
[23:21] <hmh33> oh ok you're probably golden then :D
[23:21] <jcoxon> though i wouldn't be suprised if they had similar rules
[23:26] <defy> there are rules with moored balloons, as with free balloons
[23:27] <defy> I do need to sort out a rapid deflation device
[23:27] <defy> but thats about it really
[23:29] <hmh33> James
[23:29] <hmh33> er nm, pressed enter prematurely
[23:29] <jcoxon> :-)
[23:35] Action: jcoxon wishes he had a linux box which he could ssh into instead of having to reboot to use the gumstix buildroot
[23:36] <defy> don't you run osX?
[23:37] <jcoxon> yup
[23:37] <defy> isn't there a way to build the buildroot on osx?
[23:37] <jcoxon> the buildroot branch for that is actually about 873
[23:37] <jcoxon> rather than 1200+ that we are on now
[23:37] <defy> oh, it requires a different buildroot?
[23:38] <defy> that sucks, I would have thought you'd just need some osx crosscompilers and it would work
[23:38] <jcoxon> yeah well it sort of does
[23:38] <jcoxon> just osx gcc has a few quirks
[23:38] <jcoxon> that the buildroot chokes on and I'm terrible at hacking up makefiles
[23:39] <defy> ick
[00:00] --- Wed Feb 7 2007