highaltitude.log.20090722

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[01:42] <Laurenceb> imo its worth the extra expense
[01:43] <Laurenceb> for the safety, testing, characterisation ect
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[14:14] <SpeedEvil> Thoughts - the differential pressure is on the order of 100Pa - probably. This is .1V output - 1/40th of hte range. Looking at Fig4 in the datasheet - over 10-60C the worst case tempco is 200Pa. Unlikely to be better for -55-0. - it may need a little oven - or some calibration in a freezer.
[14:15] <edmoore> there's nothing around that is cheap and easy to interface that claims to do anything below 0 degrees c
[14:15] <edmoore> was just going to recomment a sod-it-and-see approach
[14:16] <SpeedEvil> yeah
[14:18] <SpeedEvil> I'd also wonder if you would get saturation of the output stage and no useful signal at all - the minimum voltage at 0 pressure is 0.7 - if you drop that another .2 of a volt or so, the output stage might start having problems.
[14:19] <SpeedEvil> I wonder if something _really_ stupid would work.
[14:19] <SpeedEvil> Teeny little baggie of water round the sensor, and some insulation.
[14:19] <edmoore> you can bias and amp the output, maybe discharge a lithium through a resistor next to it
[14:20] <SpeedEvil> yes - I was wondering if the output stage might simply saturate at 0.6 - and not produce a signal anymore
[14:22] <SpeedEvil> I'd probably head towards a simple hack with a opamp, transistor, resistor, and a little thermistor.
[14:22] <edmoore> RocketBoy: emailed
[14:35] <RocketBoy> edmoore: thanks - that makes it easier
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[15:23] <Neslab> Hey
[15:24] <Neslab> I just joined the IRC channel
[15:25] <Neslab> I'm a member of a catalan group that want to do a high altitude balloon project
[15:26] <Neslab> All the memebers are students of aeronautical engineering
[15:26] <Neslab> We want to do some High resolution HDR pictures
[15:27] <Neslab> but we don't know how to stabilize the pod
[15:28] <SpeedEvil> HDR?
[15:28] <SpeedEvil> you mean video?
[15:29] <Neslab> no photo
[15:29] <SpeedEvil> See the above wiki and web pages
[15:29] <Neslab> to see the stars and the earth at the same time
[15:30] <SpeedEvil> All of the above were taken with no stabilisation.
[15:30] <SpeedEvil> Ah
[15:30] <SpeedEvil> Well - you do know that you will need very enormous dynamic range to see that?
[15:30] <SpeedEvil> Can your camera actually normally see stars?
[15:31] <Neslab> well we have sony suport
[15:31] <SpeedEvil> If it can't, then you obviously can't if you put it on a balloon.
[15:31] <SpeedEvil> ?
[15:31] <Neslab> so we have a alpha 900
[15:31] <Neslab> it's a good camera
[15:32] <Neslab> outstanding 24 megapixels
[15:33] <SpeedEvil> Which is irrelevant.
[15:33] <SpeedEvil> The problem is that your light area is going to be many tens of millions brighter than the dark area.
[15:34] <SpeedEvil> And it's worse if the sun is in the same direction
[15:34] <Neslab> but we need little long exposures
[15:34] <Neslab> yes thats true
[15:34] <SpeedEvil> I'm not sure you can actually get long exposures - meaningfully - if there is a sunlit earth in the frame
[15:34] <Neslab> thats what why we need so good camera
[15:35] <SpeedEvil> Can you typically see stars at night where you are?
[15:35] <Neslab> not very well
[15:36] <Neslab> the key is take 3 pictures
[15:36] <SpeedEvil> If so, point the camera at the sky, and place an A4 sheet of paper so it's half in view.
[15:36] <SpeedEvil> Now, place a 500W floodlight 1m from the sheet of paper - out of sight of hte camera
[15:37] <SpeedEvil> This is approximately the same brightness as the sunlit earth.
[15:37] <SpeedEvil> Taking three pictures doesn't help if the stars are drowned out by the .00001% of light that the lens reflects around internally.
[15:39] <russss> hmm
[15:39] <SpeedEvil> The moon is easy - as are the planets. And maybe the very brightest stars. But you are not going to get (IMO) a black sky filled with stars and a bright sunlit earth in the same frame.
[15:39] <SpeedEvil> edmoore did something vaguely related to this
[15:40] <SpeedEvil> he may have some insight.
[15:40] <SpeedEvil> (the bright planets - jupiter, saturn, venus)
[15:40] <russss> you can help things out by using graduated filters
[15:41] <russss> I've done some fairly hardcore HDR like that before
[15:41] <SpeedEvil> To an extent, yes.
[15:41] <SpeedEvil> But with a foreground several million times brighter than the image?
[15:41] <russss> but it would be a fair challenge on the ground, not least when you're swinging around on a balloon
[15:42] <SpeedEvil> I think the first thing to try is to work out if it can be done at all - if the camera can do it - on the ground at night - or indoors - with a representative brightness of 'star' - of a similar optical diameter - and a lit model of earth - or a sheet of A4 even.
[15:43] <SpeedEvil> If it can - then you move on to how to stabilise the camera, and keep it from freezing, and how to make a AR coated window that can cope with keeping the camera at 0C, and the outside at -55C - while not scattering any light.
[15:44] <russss> yeah
[15:44] <SpeedEvil> And how to recover this expensive camera, and several testflights to make sure you have a clue on protection and stuff.
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[16:21] <SpeedEvil> neslab: also - you may find http://www.flickr.com/search/?cm=sony%2Fdslr-a900&xel=30&w=all&q=night&m=text useful
[16:21] <SpeedEvil> meh
[16:24] <SpeedEvil> http://www.flickr.com/photos/bigsleep/3064523427/ fun
[16:38] <edmoore> anyone need anything from sparkfun
[16:38] <edmoore> missed the catalans, oh well
[16:40] <SpeedEvil> I need one of _everything_ from sparkfun. But meh.
[16:40] <SpeedEvil> :)
[16:42] <edmoore> SpeedEvil: ok ordered
[16:42] <edmoore> you owe us a cheque for...
[16:42] <edmoore> (hang on just calculating)
[16:43] <edmoore> call it $50,000 (mates rates)
[17:04] <edmoore> I'm not sure that those catalans realised that 'stabilising the pod' is about 98% of the battle for the entire project
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[17:06] <edmoore> Hi Neslab
[17:06] <edmoore> you are interested in the stabilisation of high altitude balloon platforms?
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[17:07] <Neslab> Yes
[17:07] <Neslab> we thinck to pu some fans
[17:07] <Neslab> or like a sail
[17:08] <Neslab> but we are not sure about it
[17:08] <Neslab> we are on preliminary design
[17:09] <Neslab> we've done litle about that
[17:09] <edmoore> i think it will be by far the hardest part of your project
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[17:10] <Neslab> yes i expect
[17:10] <edmoore> I say this given I am about to start building something almost exactly the same, for astrophotography
[17:10] <edmoore> what stage are you at - you mentioned you are aerospace students
[17:10] <edmoore> e.g. undergraduate degree?
[17:10] <Neslab> yes
[17:11] <Neslab> weel i'm not sure about the equivalence
[17:11] <Neslab> but i thinck its undergraduate
[17:11] <Neslab> later when we finish we can do a master
[17:12] <Neslab> you can follow our progress at www.neslabproject.com
[17:12] <edmoore> ok - how many of you are there and what sort of timeframe?
[17:12] <Neslab> what are your ideas about stabilitzation?
[17:13] <Neslab> well the people who is really working on this are 5 people and we spend 10 hours a week
[17:14] <edmoore> neslab if you can hang around 10 mintues i will be mroe free then
[17:14] <edmoore> just trying to place an order
[17:14] <Neslab> ok
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[17:17] <edmoore> translation fail
[17:24] <SpeedEvil> http://www.flickr.com/search/?cm=sony%2Fdslr-a900&xel=30&w=all&q=night&m=text neslab:
[17:24] <SpeedEvil> meh
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[17:31] <rjmunro> I've just been reading http://www.pegasushabproject.org.uk/wiki/doku.php/missions:ballasthalo
[17:31] <rjmunro> What were the main differences between BallastHalo 1 and BallastHalo 2? I.e. why did 2 work and 1 fail?
[17:32] <edmoore> rjmunro: much slower ascent on 2
[17:32] <edmoore> so less helium to get rid of and more time to get rid of it
[17:33] <rjmunro> Was that by putting less helium in to start with? Or a heavier payload?
[17:33] <edmoore> less he
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[17:48] <edmoore> Hi Neslab
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[17:49] <Neslab> hi
[17:49] <Neslab> so what do you think it would be good for stabilize a 2,5 payload
[17:51] <edmoore> 2.5kg?
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[17:51] <Neslab> we expect no more than 2,5 kg
[17:51] <Neslab> is it too much
[17:51] <Neslab> or too less
[17:52] <jcoxon> afternoon all
[17:53] <SpeedEvil> http://www.flickr.com/photos/hahahahahahahahaaa/2885048584/
[17:53] <SpeedEvil> nice
[17:53] <edmoore> stick around, really have to finish this order. promise to talk soon
[17:53] <SpeedEvil> http://www.flickr.com/search/?cm=sony%2Fdslr-a900&xel=30&w=all&q=night&m=text
[17:53] <SpeedEvil> Neslab:
[17:53] <SpeedEvil> this is all hte images with your camera that have a text of night, and over 30s exposure time
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[17:54] <Neslab> I know it's dificult
[17:55] <Neslab> but we can do some trick to get better pictures than the actual ones
[17:55] <Neslab> first of all we have a good lens
[17:55] <edmoore> the camera is not the issue really. stabilisation is a much harder problem. you can find cameras that'll do it
[17:55] <Neslab> so we can get this times lower
[17:56] <Neslab> second we gave a wide angle lens
[17:56] <Neslab> so we would see more
[17:56] <Neslab> maybe we don't get what humans see but ... we are going to bee a litle bit closer
[17:57] <jcoxon> hi Neslab
[17:58] <jcoxon> the key is going to be minimising the spin of the payload
[17:58] <jcoxon> the less it spins the better your results
[17:58] <Neslab> of course
[17:59] <jcoxon> and i can assure you there is lots of spin!
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[17:59] <jcoxon> perhaps the first step is to look into that - launch a small payload to measure the spin etc
[17:59] <jcoxon> it'll give you loads of launch experience
[17:59] <jcoxon> and good data
[17:59] <Neslab> we can attack the problems in two ways
[18:00] <Neslab> (we are gonna do a series of test flights)
[18:00] <Neslab> 0ne way is stabilitzation
[18:00] <Neslab> and the other is software
[18:00] <Neslab> we can do lots of pictures
[18:00] <Neslab> and then join it
[18:00] <Neslab> so the exposure it will be like one of 10 seconds
[18:01] <jcoxon> sure
[18:01] <jcoxon> in practice that might be easier
[18:02] <Neslab> http://www.flickr.com/photos/hahahahahahahahaaa/2885048584/
[18:02] <jcoxon> i think its important to get launching though, it isn't as easy as it looks - lots of things can go wrong (and do) and its important to make a good flight computer
[18:02] <Neslab> this is not what we are searching
[18:03] <Neslab> we want to get the house burned (earth) and then the stars will be alrite
[18:03] <Neslab> It's dificult
[18:03] <SpeedEvil> You have fundamental noise problems.
[18:03] <Neslab> ¿?
[18:04] <SpeedEvil> You _might_ be able to attack this by stacking tens or hundreds of thousands of pics.
[18:04] <SpeedEvil> But I have doubts.
[18:04] <SpeedEvil> Yes - you have a good lens. And a good camera.
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[18:04] <SpeedEvil> However - you're asking it to do a _very_ extreme thing - the top half of the image is over a million times dimmer than the bottom.
[18:05] <jcoxon> SpeedEvil, point it up
[18:05] <jcoxon> sure you'll get the balloon
[18:05] <SpeedEvil> yes - that's trivial to do
[18:05] <jcoxon> but you'll reduce that issue a bit
[18:05] <rjmunro> Neslab: What exactly are you trying to do?
[18:05] <SpeedEvil> Getting stars is - comparatively - easy.
[18:05] <jcoxon> the person to talk to is edmoore really
[18:05] <SpeedEvil> Getting stars and a sunlit earth in the same shot is very not easy.
[18:05] <Neslab> nobody said it gonna be easy
[18:05] <edmoore> i'm just a tiny bit busy, i will be free soon. Imthink I can help you with this stabilisation issue
[18:06] <Neslab> We want to take hdr pictures
[18:06] <SpeedEvil> easy - or indeed possible with your camera.
[18:06] <Neslab> what about you?
[18:06] <Neslab> what are you doing?
[18:06] <SpeedEvil> Neslab: you cannot take HDR pictures if your camera cannot cope with the levels of light without blooming, or other artefacts.
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[18:07] <SpeedEvil> Sure - you can have the foreground completly saturated. But there will still be light from that foreground bouncing around the lens.
[18:07] <jcoxon> Neslab, I've just launched a latex floater flight, got it to float for just over 7hrs
[18:07] <jcoxon> thats what i've been doing
[18:08] <jcoxon> :-)
[18:08] <Neslab> great!!!
[18:08] <SpeedEvil> HDR improves the dynamic range of the camera - however there are limits beyond which you can't go with just software.
[18:08] <Neslab> we are going to explore what we can do and what we can not.
[18:08] <Neslab> It's simple
[18:09] <SpeedEvil> Try the above test - 500W floodlight illuminating A4 sheet of paper from 1m at night in the shot of the camera, and see what you can see at night.
[18:09] <jcoxon> Neslab, go for i reckon :-)
[18:09] <jcoxon> it'll be fun trying
[18:09] <SpeedEvil> Yep. There are fun pictures that can be got.
[18:11] <Neslab> thanks for the test idea
[18:11] <rjmunro> This is reminding me of moon landing conspiracies - why there are no stars in the sky in photos from the moon.
[18:11] <SpeedEvil> IIRC the astronauts also said they couldn't see stars normally
[18:11] <SpeedEvil> in daytime
[18:14] <rjmunro> (IMHO if they were faked in a studio somewhere, they /would/ have put stars in the photos :-)
[18:15] <SpeedEvil> They faked them on mars - I thought everyone knew that. There were no moon landings.
[18:16] <SpeedEvil> Neslab: what sort of skills does your group have?
[18:16] <SpeedEvil> Neslab: and what have you done before?
[18:16] <Neslab> question: what means red nicks?
[18:17] <Neslab> we are students of aerospace engineering
[18:17] <Neslab> and this is the first time we attempt to flight a balloon
[18:18] <SpeedEvil> red nicks?
[18:18] <SpeedEvil> that may be your client highlighting hte line if your name is mentioned.
[18:18] <Neslab> ok thanks
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[18:30] <Neslab> wich ballon should we choose?
[18:30] <edmoore> Neslab: hi
[18:30] <edmoore> sizr that after your payload is done
[18:30] <edmoore> 1.5kg are pretty standard though
[18:31] <Neslab> kaymont ones?
[18:31] <edmoore> yeah
[18:33] <natrium42> ohai
[18:34] <Neslab> KKS ?
[18:34] <edmoore> never heard of them. we all use kaymont
[18:36] <Neslab> why?
[18:37] <Neslab> They are from japan
[18:37] <Neslab> they have the same sizes but bigger final diameters
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[18:40] <edmoore> we have a uk supplier for the kaymont ones
[18:40] <edmoore> anyway, the tricky bit is stabilisation
[18:40] <edmoore> does anyone on your team have much experience with control engineering?
[18:40] <Neslab> no
[18:40] <Neslab> we have no experience of nothing
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[18:41] <edmoore> ok
[18:41] <edmoore> how is your maths?
[18:41] <Neslab> pretty good
[18:41] <edmoore> statistics and linear algebra
[18:41] <Neslab> good
[18:41] <edmoore> i need to eat, then i will return
[18:41] <edmoore> try that link
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[18:42] <edmoore> wikipedia is not very good, but for good control of this kind of thing you need predictive control and state estimation, and the kalman filter forms a large part of that theory
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[18:42] <edmoore> you'll need it for interpreting your sensors and getting the best estimate of your state (position and turning rates)
[18:43] <edmoore> the actuation for control is more arbitrary - be in mometum wheels or fans or whatever
[18:43] <edmoore> i will be back in about 20 mins
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[18:43] <Neslab> thanks
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[19:07] <edmoore> bk
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[19:33] <Neslab> edmoore: so wich are youre ideas for stabilize the payload
[19:39] <edmoore> Neslab: reaction wheels
[19:39] <Neslab> oh the kalman filter is a must for controlling but we are now far away from this type of analysis. We are trying to get something that flies first.
[19:39] <Neslab> Reaction wheels are heavy
[19:40] <Neslab> why not something new
[19:40] <edmoore> depends on how much rotational inertia you give them
[19:41] <Neslab> Fans, Weather vane
[19:41] <Neslab> if the controll is passive the better
[19:41] <edmoore> My assessment was that you cannot get nearly enough fidelity from fans
[19:41] <edmoore> however my pointing requirements might be tigther than yours
[19:42] <edmoore> i don't think passive control will be at all possible
[19:42] <edmoore> honestly
[19:42] <edmoore> too many torques up there, vortices being shed by the balloon and so on
[19:42] <edmoore> also the thing travels at the same speed as the wind so there is no dynamic pressure in latitude/longitude
[19:43] <edmoore> just your slow vertical ascent
[19:43] <jcoxon> edmoore, wow 36
[19:43] <edmoore> tell me about it!
[19:44] <jcoxon> welcome to highaltitude new people e.g. G8DSU_ shauno str4nd
[19:45] <str4nd> Thanks :)
[19:49] <edmoore> Neslab: the point of that being that I don't think weather vanes would work
[19:49] <edmoore> and fans aren't passive
[19:49] <Neslab> yes it's true
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[19:50] <Neslab> we will have to test them
[19:51] <Neslab> but vanes will also make harder to change the attitude of the vehicle
[19:51] <Neslab> are dissipative
[19:51] <Neslab> if they are big enough
[19:51] <Neslab> of course
[19:52] <edmoore> they damp
[19:52] <edmoore> they won't correct for 'integral' error, eg constant torque from balloon string
[19:52] <Neslab> it's true
[19:53] <Neslab> will lower the effect
[19:54] <Neslab> diminish
[19:55] <edmoore> sure, but even a 10 second exposure is a very long time if you want a start to look like a star
[19:59] <Neslab> decoupling the movement of the balloon it will also be a good thing to do.
[19:59] <edmoore> that depends on your control scenario
[20:00] <edmoore> you might wat to, say, desaturate a reaction wheel through the balloon tether
[20:00] <Neslab> yes
[20:00] <Neslab> true
[20:02] <edmoore> what sort of pointing accuracy are you looking at?
[20:02] <edmoore> I want to specifically point at regions of the night sky and do some astrophotography - that mayb be a somewhat more stringeant requirement than for you
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[20:04] <Neslab> yes much more
[20:04] <Neslab> at first we want, as I said, just a fly with good pictures
[20:05] <Neslab> then at least stabilitzation without pointing
[20:05] <edmoore> oh well that's certainly possible
[20:05] <Neslab> and after that pinting
[20:05] <Neslab> pointing
[20:05] <edmoore> if I may plug our flickr site, http://www.flickr.com/photos/cuspaceflight
[20:05] <Neslab> but we are not sure about that.
[20:06] <edmoore> and our site is cuspaceflight.co.uk
[20:06] <edmoore> all the photos are passive - no active control
[20:06] <edmoore> check out 'nova 10 launch' on the media page to see one of our approaches for passive stabilisation
[20:07] <Neslab> this is like jp aerospace with the ads
[20:07] <edmoore> last call for sparkfun jcoxon SpeedEvil RocketBoy gordonjcp SpikeUK
[20:07] <edmoore> or anyone else
[20:07] <jcoxon> edmoore, nothing from me
[20:07] <fergusnoble> Neslab: yeah we have to get funding from somewhere
[20:07] <edmoore> Neslab: we have to fund this hobby somehow :) we get nothing from the university
[20:07] <SpeedEvil> edmoore: Much I want, none I need. :) Good luck with aht you're getting.
[20:08] <SpikeUK> edmoore - I'm fine thanks!
[20:09] <Neslab> how much weight is on that?
[20:09] <edmoore> Neslab: from the nova 10 video you can see that the angular rates are very low. drapes kept it really quite stable
[20:09] <edmoore> about 3kg
[20:09] <edmoore> it's just a small box really - the drapes weigh nothing
[20:10] <Neslab> pretty good
[20:14] <fergusnoble> Neslab: did you have any thoughts on how you were going to do stabilisation?
[20:15] <Neslab> not really
[20:15] <Neslab> we are just now discussing the options
[20:15] <fergusnoble> yup
[20:16] <fergusnoble> you want to take long exposures to get stars?
[20:16] <fergusnoble> just reading back over what you and ed were saying
[20:18] Action: SpeedEvil wishes consumer cameras published proper numbers.
[20:18] <SpeedEvil> (quantum efficiency, dark current, SNR)
[20:18] <fergusnoble> reaction wheels are a good way to go i think if you are willing to take on the complexity
[20:18] Action: SpeedEvil wishes stuff superconducted at -55C.
[20:19] <SpeedEvil> Maglev bearings.
[20:19] <fergusnoble> they can be quite light if you put all the mass far from the axis of rotation
[20:20] <SpeedEvil> For starlike pictures of stars - over a (say) 1s period, with a 24MP cam - tricky
[20:20] <SpeedEvil> Neglecting for the moment the dynamic range issue
[20:20] <SpeedEvil> I don't know how far you can meaningfully go down, and stack in software.
[20:21] <fergusnoble> and with the kinds of angular frequencies you can get direct drive from an electric motor you dont need sill amounts of moment of inertia to get an angular momentum comparable to a swinging payload
[20:21] <fergusnoble> SpeedEvil: some post-processing will help a lot
[20:21] <fergusnoble> got a good link - 1 sec
[20:21] <edmoore> on the ccd issue, their response is non linear
[20:21] <edmoore> so 10 x 1s exposure != 1x 10s exposure
[20:22] <fergusnoble> http://sweaglesw.com/cs448/
[20:22] <SpeedEvil> edmoore: yes, I know - readout noize.
[20:22] <SpeedEvil> and stuff.
[20:22] <SpeedEvil> But - 10s exposures are going to be much harder than .1s
[20:22] <fergusnoble> to put it in perspective, with henry's startracker that i helped on the readout noise was the same order as the signal
[20:22] <fergusnoble> so its a real killer
[20:23] <edmoore> this is why I want to be a bit anal about getting the control system as good up in the air as poss. deconvolution and other post-processing is more of a plaster to a wound you've already got. though still very useful. Confess I have to read up on that bit more, most of my focus has been on the control system
[20:23] <SpeedEvil> fergusnoble: yes - IIRC that was a very bad - comparative to some of the CCDs out there - imager.
[20:24] <fergusnoble> yeah it wasnt great
[20:24] <SpeedEvil> But the nice ones arne't cheap and easily available.
[20:24] <Neslab> Thanks for the advice
[20:24] <fergusnoble> but it was the kind of ballpark you get with sensors you can buy individually
[20:24] <SpeedEvil> I wish the TI impactron was available. That's nice - it's got a solid state image amp.
[20:24] <fergusnoble> if you use a proper camera yup its a lot better
[20:24] <SpeedEvil> fergusnoble: I was meaning compared to sensors you would readout lots slower
[20:25] <fergusnoble> the monochrome sensors are also a lot better i think
[20:25] <fergusnoble> mainly just because you dont have to deal with the bayer stuff
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[20:28] <SpeedEvil> That helps, yes.
[20:28] <rjmunro> What effect does the cold have on the sensor?
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[20:29] <SpeedEvil> good.
[20:29] <SpeedEvil> Generally
[20:29] <SpeedEvil> It lowers thermal noise - if that's an issue for your sensor.
[20:29] <SpeedEvil> For some it's not
[20:30] <edmoore> rjmunro: for fun, if you put lens cap on your camera and take a really really long exposure, you may see the lines where the current is carried underneath showing through as brightly glows
[20:30] <edmoore> brighter*
[20:31] <SpeedEvil> There are lots of reasons for image sensor suckage.
[20:32] <fergusnoble> rjmunro: henry and I got some very odd looking images by doing that
[20:32] <SpeedEvil> From the fundamental physics - there are only so many photons - to the fact that the sensor would be $.1 more expensive if they fixed 'x'.
[20:32] <fergusnoble> we could see the bonding wires onto the die because the sunk heat away and left darker shadows
[20:33] <fergusnoble> http://www.srcf.ucam.org/~cuspaceflight/websvn/filedetails.php?repname=CUSF&path=%2Fstar+tracker%2Fhenrypython%2Fcaptures+etc%2Fbga+pins.jpg
[20:33] <fergusnoble> thats the one
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[21:06] <rharrison_eee> yey
[21:06] <rharrison_eee> hey even
[21:06] <rharrison_eee> this keyboard is so small
[21:06] <edmoore> rharrison_eee: was separate from phone earlier, just spotted you called
[21:07] <rharrison_eee> Yep accidental call
[21:07] <rharrison_eee> Last number diled
[21:07] <edmoore> ok cool
[21:07] <rharrison_eee> I'm going to order up that sensor noe
[21:07] <rharrison_eee> w
[21:09] <rharrison_eee> Will be fun getting that to work. I'm going to make the assumption that the balloon pressure will be > or = to ext pressure
[21:09] <rharrison_eee> I cant imagine a case where it would be less in a flexible envelope
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[21:23] <jcoxon> damn damn, sourceforge downloads are down
[21:24] <jcoxon> ooo another source
[21:53] <edmoore> jcoxon: what are you downloading?
[21:53] <jcoxon> :-)
[21:53] <jcoxon> some python libraries
[21:54] <jcoxon> got them now
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[22:00] <rharrison_eee> ed
[22:00] <rharrison_eee> edmoore:
[22:01] <edmoore> hi
[22:01] <rharrison_eee> The sensor you linked is 10v
[22:01] <rharrison_eee> I have found similar 3v
[22:01] <rharrison_eee> This makes interfacing simple
[22:01] <SpeedEvil> link?
[22:01] <edmoore> see later email
[22:01] <rharrison_eee> Can you have a quick glance or am I missing something
[22:01] <edmoore> 4-5V
[22:01] <edmoore> i found a better one earlier
[22:01] <edmoore> hang you on
[22:02] <SpeedEvil> edmoores one has a simple output, not differetneigla
[22:02] <rharrison_eee> http://uk.farnell.com/jsp/search/browse.jsp?N=1004544+329844+383759&No=0&getResults=true&appliedparametrics=true&locale=en_UK&prevNValues=1004544+329844&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D1004544%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK
[22:02] <edmoore> looks alright to me
[22:03] <rharrison_eee> There are a few here
[22:03] <SpeedEvil> look at the outputs though
[22:03] <edmoore> the 10dp should work in the range
[22:03] <SpeedEvil> 2.5mV/Kpa
[22:03] <SpeedEvil> and you're looking at about .1KPa
[22:04] <edmoore> that's bizarre
[22:04] <edmoore> a 0-10kPa sensor with 2.5mV/kPa
[22:05] <SpeedEvil> It's not really
[22:05] <rharrison_eee> http://uk.farnell.com/freescale-semiconductor/mpx10dp/sensor-diff-press-1-45-psi-344c/dp/1457144
[22:05] <SpeedEvil> it's cheaper to make unamplified
[22:05] <edmoore> sure, well it would certainly need an amp
[22:05] <rharrison_eee> I'm going for this subject to anyone saying no
[22:05] <edmoore> SpeedEvil: how far back does your client scroll?
[22:05] <edmoore> i have lost the stuff i posted earlier today
[22:06] <rharrison_eee> I'll wait a sec
[22:06] <rharrison_eee> I'm looking for easiest to implement
[22:07] <SpeedEvil> 30C delta-t gives you the same order of magnitude as the signal
[22:07] <SpeedEvil> hang on
[22:08] <RocketBoy> I concurr with SpeedEvil - the pressure difference for KCI1500 at burst will be about 0.16kPa (1.6hPa = 1.6mill bar) according to the Totex data
[22:08] <SpeedEvil> edmoore: !msg rjharrison this the is differential pressure to go for, I think. You live next to farnell so can probably get one, if not, if you catch me before the end of the day we'll order a couple with another order we're putting in http://uk.farnell.com/freescale-semiconductor/mpxv5004dp/sensor-pressure/dp/1457165?in_merch=true&
[22:09] <edmoore> there we go
[22:09] <SpeedEvil> RocketBoy: do they say anything about what happens before that? I think that the pressure should drop all the way from inflation to burst
[22:09] <edmoore> 1.0V/kPa
[22:09] <rharrison_eee> Perfect
[22:09] <SpeedEvil> The temperature drift and stuff are as bad - but you don't need an external amp
[22:09] <rharrison_eee> I'll get a couple tomorrow
[22:10] <edmoore> and 5V
[22:10] <edmoore> I think various people have estimated of the order of 3kPa on the ground
[22:10] <edmoore> DP
[22:11] <rharrison_eee> Well we'll know soon
[22:11] <rharrison_eee> I could do with getting an actual pressure sensor too
[22:12] <rharrison_eee> Bee good to know ext pressure
[22:12] <rharrison_eee> Icarus III is going to be we loaded
[22:12] <rharrison_eee> s/we/well
[22:13] <rharrison_eee> Int/Ext Temp + DPpressure and abs pressure
[22:13] <edmoore> the same freescale range does some absolute ones
[22:13] <edmoore> we can make good guesses at abs pressure though
[22:14] <edmoore> from gps alt and temp
[22:15] <rharrison_eee> Ok but would be cool to have?
[22:15] <edmoore> oh def
[22:15] <edmoore> scp1000 is a good candidate
[22:15] <edmoore> ...and we're putting in a sparkfun order tomorrow
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[22:17] <edmoore> right, am off. may be back briefly later. fergus and I going for a drink to discuss amsat talk (watch it live online! plug plug)
[22:18] Nick change: edmoore -> edmoore|away
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[23:26] <Laurenceb> hi
[23:26] <Laurenceb> whats new?
[23:28] <RocketBoy> edmoore: some interesting results when inflating an ordinary latex big party balloon:
[23:28] <RocketBoy> started to inflate at 19mbar
[23:29] <RocketBoy> then pressure dropped to 14mbar as further inflating
[23:29] <RocketBoy> then it rose again - finally bursting at 31mbar
[23:30] <RocketBoy> the biggest pressure rise was just before burst
[23:31] <RocketBoy> I don't see why metrological balloons would be much different in profile - we know the pressures are much smaller
[23:31] <Laurenceb> it reached the yeild point
[23:31] <Laurenceb> elastic limit even
[23:32] <RocketBoy> there was some conjecture earlier that burst pressure would be lower than inflation pressure - which seemed counter experiance when blowing up party balloons
[23:35] <RocketBoy> still a similar pressure profile would still put met balloon pressure in the 1 to 3 milli bar region
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[23:47] <rjmunro> I wondered about estimating pressure inside the balloon by measuring the rate the helium escapes through the hole.
[23:49] <SpeedEvil> and how do you measure that?
[23:49] <SpeedEvil> it's in principle possible
[23:50] <SpeedEvil> RocketBoy: that was based on the fact that it's a lot harder to 'start' a balloon than it is to continue blowing it up
[23:51] <SpeedEvil> It's been too long since I played with balloons :)
[23:52] <Laurenceb> brb
[23:53] <RocketBoy> measured with a column of water - about 1cm of column per mb I calculate
[23:54] <SpeedEvil> sounds right
[23:54] <RocketBoy> yeah - your right its harder to start - but it seems to get easier then harder again
[23:55] <SpeedEvil> I'd assumed it was elastic all the way to the yield
[23:55] <SpeedEvil> That's a bit dubious on reflectoin.
[23:56] <SpeedEvil> Did you mention earlier the burst pressure?
[23:56] <RocketBoy> 31mbar
[23:56] <SpeedEvil> err - of the big ones
[23:57] <RocketBoy> oh yeah about 1.6mbar as I calculate from the data
[23:58] <SpeedEvil> I concurr with SpeedEvil - the pressure difference for KCI1500 at burst will be about 0.16kPa (1.6hPa = 1.6mill bar) according to the Totex data
[23:58] <SpeedEvil> that is computed - or a datasheet value?
[23:59] <RocketBoy> computed from http://www.kaymont.com/pages/sounding-balloons.cfm
[23:59] <RocketBoy> based on volume at release, diameter at burst, burst pressure
[00:00] --- Thu Jul 23 2009