highaltitude.log.20090801

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[01:02] <rjharrison> sleepy
[01:02] <rjharrison> I think it's time
[01:03] <rjharrison> To nurse my blister and go to bed
[01:03] <rjharrison> I'll get ADC wo
[01:03] <rjharrison> rking tomorrow
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[08:42] <jcoxon> morning rjharrison
[09:13] <rjharrison> Hey
[09:13] <rjharrison> jcoxon
[09:13] <rjharrison> Whats you math like
[09:15] <rjharrison> Linear relationship means line on graph. This means y=mx+c. Solve for 2 known points and I have the equation needed for my pressure sensor
[09:15] <rjharrison> It's early I know :)
[09:16] <jcoxon> my maths is terrible
[09:16] <jcoxon> sorry
[09:18] <rjharrison> You're excused your a Dr :)
[09:18] <rjharrison> You're excused you're a Dr :)
[09:18] <rjharrison> Presure sensor is cool
[09:18] <rjharrison> Just calibrating. Need to make up new pcb
[09:19] <jcoxon> great
[09:20] <jcoxon> i'm just putting a php page together
[09:20] <jcoxon> to run my cusfpredict/hysplit fusion
[09:23] <rjharrison> Cool
[09:23] <rjharrison> I'm doing house stuff during the day today
[09:23] <jcoxon> i'm off sailing in a bit :-)
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[09:58] <jcoxon> rjharrison, you around?
[10:00] <jcoxon> actually no worries
[10:00] <jcoxon> fixed it
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[10:27] <rjharrison> boo
[10:27] <rjharrison> jcoxon about to go
[10:27] <rjharrison> .
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[11:12] <edmoore> g'morning djellison
[11:18] Nick change: kingj -> KingJ
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[14:24] <Laurenceb> hi
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[15:01] Action: SpeedEvil has been out killing.
[15:01] <SpeedEvil> Weeds.
[15:05] <Laurenceb> http://wiki.ukhas.org.uk/projects:stratogulp_return_to_launch_system_for_high_altitude_balloon_payloads
[15:05] <Laurenceb> looks interesting
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[15:05] <Laurenceb> I'd be interested in the processor
[15:07] Action: SpeedEvil again wishes that small imager chips were available.
[15:07] <SpeedEvil> The wii one would be lovel.y
[15:07] <Laurenceb> thats a daft way to do it
[15:07] <Laurenceb> IMU is the way to go
[15:07] <SpeedEvil> I mean - for other projects.
[15:07] <Laurenceb> fairdoos
[15:07] <SpeedEvil> Consider a sun sensor using the builtin brightest spot of the wii camera
[15:08] <SpeedEvil> you readout directly the x and y orientation of the sun.
[15:08] <SpeedEvil> All you need is maybe 4-6 cameras, and you've got a nice really precise axis easily.
[15:08] <SpeedEvil> (of course weather dependant)
[15:08] <SpeedEvil> (and you want to take care about reflections of the sea too)
[15:09] <SpeedEvil> Add a magnetometer, and you've got pretty much absolute orientation.
[15:09] <SpeedEvil> (for certain times of day where they are well seperated
[15:10] <Laurenceb> 6 cameras ?!
[15:11] <Laurenceb> for a UAV you can use accel usually
[15:11] <SpeedEvil> 90 degree or so FOV
[15:11] <SpeedEvil> 360 degree coverage
[15:12] <SpeedEvil> And they are well under a gram each
[15:12] <Laurenceb> yeah but it results in quite a lot of data flow
[15:12] <Laurenceb> not so much processing, but lots of data out of the cameras
[15:13] <SpeedEvil> Nope.
[15:13] <SpeedEvil> The wii camera can actually output x/y position of the brightest n (up to 10) centroids.
[15:13] <SpeedEvil> All you need to do is to read them out
[15:14] <Laurenceb> ah
[15:14] <Laurenceb> well... wii cameras are cheap?
[15:15] <SpeedEvil> No, you can't get them.
[15:15] <SpeedEvil> the actual camera would be about $1 - if you could get it.
[15:15] <Laurenceb> http://www.myit-media.de/the_end.html
[15:15] <SpeedEvil> Do you want 99990? :)
[15:16] <SpeedEvil> Not doing flash at the moment, owing to hte fucking huge vulnerability.
[15:16] <Laurenceb> buy the product?
[15:16] <SpeedEvil> yeah - 6 wii controllers aren't cheap anymore alas.
[15:17] <Laurenceb> probably compared to the crazy prices sparkfun charge for their imu
[15:17] <Laurenceb> the analogue devices IMU is better - if you can get a single one...
[15:17] <Laurenceb> digikey have a large markup
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[15:39] <Laurenceb> I'm not convinced that the high G from a 2 stage solid design will damage the propellant
[15:39] <SpeedEvil> why not?
[15:39] <Laurenceb> as theres some very short burn time motors that are going to have similar accel
[15:39] <Laurenceb> with the stock motor case
[15:39] <SpeedEvil> hmm.
[15:40] <SpeedEvil> Can you email them?
[15:40] <Laurenceb> maybe... not sure how helpful they would be
[15:40] <Laurenceb> but I guess its pretty important for regular customers
[15:40] <Laurenceb> another thing is that at burnout the propellant layer on the wall is going to be very thin
[15:41] <Laurenceb> so the shear stress is lowered
[15:41] <Laurenceb> wheras the short burn time motors have complex geometeries that concentrate stress
[15:42] <Laurenceb> http://pro38.com/products/pro75/motor/MotorData.php?prodid=4864L2375-P <- can you see the graph?
[15:42] <Laurenceb> I get "missing plugin"
[15:42] <Laurenceb> but then "no plugins found"
[15:46] <SpeedEvil> ...
[15:46] <Laurenceb> from the nozzle dimensions and the test data it looks to me like they are using AP/Al/HTBT propellant mixture, which can give an ISP of over 300 with a huge nozzle in vacuum
[15:47] <SpeedEvil> http://en.wikipedia.org/wiki/Uni
[15:47] <SpeedEvil> err
[15:47] <Laurenceb> 250 is conservative with about 25 times expansion
[15:47] <Laurenceb> I know what one of those is :P
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[15:47] <SpeedEvil> images/4864L2375-P.pdf
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[15:47] <SpeedEvil> inspecting the source
[15:48] <DanielRichman> Laurenceb, http://pro38.com/products/pro75/motor/images/4864L2375-P.pdf
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[15:48] <Laurenceb> doh missed the pdf
[15:48] <Laurenceb> thanx
[15:48] <DanielRichman> they tried to <embed> a pdf
[15:48] <SpeedEvil> http://pro38.com/products/pro75/motor/images/4864L2375-P.pdf
[15:48] <DanielRichman> Don't think Ubuntu is happy with that
[15:48] <DanielRichman> so just used view source to find the original
[15:49] <Laurenceb> nice and smooth
[15:50] Action: SpeedEvil ponders cooking.
[15:52] <Laurenceb> hmm the http://pro38.com/products/pro75/motor/MotorData.php?prodid=3757L800-P ramps bown rather nicely
[15:52] <Laurenceb> *down
[15:52] <Laurenceb> argg
[15:56] <Laurenceb> hmm <200G max for the 2486K510-P
[15:57] <SpeedEvil> Wher'd be the acceleration peak on that?
[15:57] <SpeedEvil> the 4s mark?
[15:58] <Laurenceb> about 135G at 4.5 seconds
[15:58] <Laurenceb> http://pro38.com/products/pro75/motor/images/2486K510-P.pdf
[16:00] <Laurenceb> you should be able to increase the burntime by reducing the chamber pressure
[16:00] <Laurenceb> at the expense of a bigger nozzle
[16:00] <SpeedEvil> this is stage 2?
[16:00] <Laurenceb> yes
[16:00] <Laurenceb> giving ~5.5Km/sec delta v
[16:00] <Laurenceb> 13% mass fraction
[16:01] <Laurenceb> which should be feasible as its just a ~1Kg CF spun solid with a 20 gram payload on the top
[16:02] <Laurenceb> the first stage then needs about 3Km/sec delta v which looks pretty feasible
[16:03] <Laurenceb> about 600 grams dry mass for the first stage
[16:04] <Laurenceb> and staying with 5Kg GLOW
[16:06] <SpeedEvil> This is still from 25km or so?
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[16:06] <SpeedEvil> Or 30 even - for 5Kg isn't bad
[16:06] <Laurenceb> yeah 30
[16:06] <Laurenceb> drag kills small stuff like this
[16:07] <Laurenceb> it looks like its very easy to do it for <£1K if you recover the first stage
[16:08] <Laurenceb> unfortunately first stage costs about £3K + fuel
[16:09] <SpeedEvil> first stage is solid?
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[16:09] <SpeedEvil> I'm forgetting what incarnation you're on now.
[16:09] <SpeedEvil> Or did you move to nuclear lightbulb already.
[16:09] <Laurenceb> yes
[16:09] <Laurenceb> heh
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[16:09] <Laurenceb> a long burning cesaroni motor
[16:10] <Laurenceb> with thrust vectoring nozzle operated by rs485 servos
[16:10] <SpeedEvil> Is that like macaroni, but with more oxidiser?
[16:10] <Laurenceb> heh
[16:10] <Laurenceb> I need to draw some diagrams
[16:11] <Laurenceb> I think this is the most feasible launch vehicle possible really ... you may be able to go smaller but its diminishing returns
[16:11] <Laurenceb> key is recovering the expensive stuff in the first stage
[16:12] <SpeedEvil> I don't know if the nprie allows that
[16:13] <SpeedEvil> I mean - say I enter a 4 million quid ssto - with 500 quid of fuel as the only cost
[16:15] <Laurenceb> I think its consumables per flight only
[16:16] <Laurenceb> the launch budget must be within £999.99 (about $1500) - and must include the launch vehicle, all of the required non-reuseable launch equipment hardware, and propellant
[16:17] <Laurenceb> first stage is reuseable launch equiptment :P
[16:17] <SpeedEvil> where's the expensive stuff on the first stage?
[16:18] <SpeedEvil> the servos and the electronics?
[16:18] <Laurenceb> yes
[16:18] <Laurenceb> and the titanium and lauminium alloy parts for thrust vectoring
[16:18] <Laurenceb> CNC milled
[16:20] <Laurenceb> at least the aluminium bottom bulkhead that doubles as a servo mount and part of the ball joint assembly for vectoring
[16:24] <Laurenceb> "the capability for multiple launches using the same refurbished equipement must be demonstrated"
[16:25] <SpeedEvil> ah
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[16:58] <Laurenceb> http://www.generalfusion.com/t5_general_fusion.php
[17:00] <SpeedEvil> I have extreme doubts.
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[17:04] <SpeedEvil> Hmm.
[17:04] <SpeedEvil> I wonder what happens if you upsize the chamber a little, swap the lead for lithium.
[17:04] <SpeedEvil> Do you get a fucking huge fusion bomb with no need of fissionables.
[17:05] <Laurenceb> lol
[17:06] <SpeedEvil> The scaling would probably mean it's not much use for other than doomsday weapons though.
[17:06] <SpeedEvil> Assuming that the neutrons are enough to light off the lithium.
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[18:48] <Laurenceb> DanielRichman: your SD card solution sounds good
[18:48] <Laurenceb> I opted for something slightly different
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[18:48] <Laurenceb> create sectors of whatever small size you want, then have each one have a header byte
[18:49] <Laurenceb> then write a used or unused notification code to that byte
[18:49] <Laurenceb> depending if the sector is used
[18:49] <Laurenceb> thwen use a binary search algorythm to find the first empty sector
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[18:52] <Laurenceb> solves the problem of flash lifetime
[19:01] <akawaka> how would you use a binary search in that situation?
[19:03] <Laurenceb> if you have 1024 sectors, try 512, then add or subtract 256 ect
[19:08] <akawaka> yeah, but how do you determine where you add or subtract 256?
[19:08] <Laurenceb> read the ststus byte
[19:09] <akawaka> but the status byte just tells you whether the current sector is user or not, right?
[19:09] <akawaka> s/user/used/
[19:09] <Laurenceb> yes
[19:10] <Laurenceb> so if sector 512 is used, try 512+256
[19:10] <Laurenceb> otherwise 512-256
[19:12] <akawaka> i see, so you are just finding the first unused sector
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[19:12] <akawaka> rather than finding any unused sector in a set of used and unused sectors
[19:13] <rjharrison> hey DanielRichman how is your SD card code going
[19:13] <rjharrison> Did you manage to debug the problems.
[19:29] <DanielRichman> rjharrison, it works!
[19:32] <rjharrison> hey guys some input here. I have pressure sensor connected to ADC and it gives values 43-191 the range is 0 to 3.97kpa. The values are linear therefor y=mx+c Solving for max and min give m as 26.666 and c as -1173.3
[19:32] <rjharrison> Is this a good way to calibrate the system?
[19:32] <rjharrison> DanielRichman cool
[19:32] <rjharrison> so how much can you write to the card?
[19:32] <DanielRichman> can write the whole card apart for the first quarter-megabyte
[19:32] <DanielRichman> really I should fix that
[19:33] <DanielRichman> but it works
[19:33] <rjharrison> and does it manage to survive a reboot with out over writing existing data
[19:34] <rjharrison> Ie how does it keep track of where is written to and where is free
[19:34] <DanielRichman> Superblock in sector 0, contains position to start at. Updated every quarter megabyte. Writes it three times and deduces the correct value
[19:34] <DanielRichman> upon restart skips a potentially part-written quarter megabyte
[19:34] <rjharrison> Cool
[19:34] <rjharrison> I see
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[19:34] <rjharrison> and what is the smallest write size
[19:34] <rjharrison> Hi jcoxon
[19:34] <DanielRichman> there isn't one
[19:35] <rjharrison> DanielRichman cool so I could write say a byte at a time
[19:35] <DanielRichman> define a function, that returns a character to write, can be from a buffer, ours generates the character based on the gps data struct
[19:35] <jcoxon> ello
[19:35] <DanielRichman> return 0 when you want to write no more data, and it will stop SCK and sleep
[19:35] <rjharrison> DanielRichman cool
[19:35] <DanielRichman> (the sd card will idle, it won';t flush data to disk()
[19:35] <rjharrison> and you interface using spi
[19:35] <DanielRichman> call log_start
[19:35] <DanielRichman> to re-start writing.
[19:35] <Laurenceb> I'd try the status byte technique maybe?
[19:36] <Laurenceb> rather than the superblock
[19:36] <DanielRichman> yeah. That'd be good, although, i'd have to know the size of the disk
[19:36] <Laurenceb> yeah
[19:36] <DanielRichman> hard code or otherwise
[19:36] <rjharrison> hey Laurenceb
[19:36] <Laurenceb> theres code on the wiki I wrote for the mini rogallo
[19:36] <Laurenceb> hi
[19:37] <rjharrison> missed you there in list
[19:37] <rjharrison> How's it going.
[19:37] <rjharrison> DanielRichman well done
[19:37] <rjharrison> BTW how big is the code?
[19:37] <Laurenceb> ok, fraid I wont be free this weekend to try a recovery
[19:37] <rjharrison> Laurenceb NP
[19:38] <DanielRichman> rjharrison, hangon, let me compile it
[19:38] <rjharrison> I have just brought a house so a little busy here too
[19:38] <DanielRichman> text data bss dec hex filename
[19:38] <DanielRichman> 1252 5 19 1276 4fc log.o
[19:38] <rjharrison> Just been in demolition mode today
[19:38] <rjharrison> wow excellent
[19:39] <DanielRichman> Though that doesn't include our gps data struct that it pulls data from
[19:39] <DanielRichman> which is ~40bytes
[19:39] <DanielRichman> (however there's 4 of them)
[19:39] <DanielRichman> ((but log only needs one))
[19:39] <rjharrison> can you read the date back using linux|?
[19:39] <rjharrison> dd
[19:39] <DanielRichman> yeah
[19:40] <DanielRichman> can even `strings /dev/sdb`
[19:40] <rjharrison> hehe cool
[19:40] <DanielRichman> I might update it with the considerations above, but they're tweaks not bugfixes, so it's essentially working
[19:40] <rjharrison> I may come begging for that code one day. I fancy been able to write data to an sd card as well as tx
[19:41] <DanielRichman> http://code.google.com/p/alien-flightcomputer/source/browse/#svn/trunk/alien1/atmega162/final
[19:41] <rjharrison> cool
[19:41] <DanielRichman> using it on the arduino is easy - just need to change the PORT and PINs
[19:41] <rjharrison> atmega168 for me
[19:42] <DanielRichman> yes. I had a hack to change the pins so that i could test it on the arduino/168. it was a C file that #undef'd PB3 through 6 and redefined them with the pin names for the Arduino, then included the real c file
[19:42] <DanielRichman> http://code.google.com/p/alien-flightcomputer/source/browse/trunk/misc-c/arduino-168/logtest.c
[19:45] <rjharrison> DanielRichman don't suppose you have the sd interface circuit around or is it up there
[19:45] <DanielRichman> I'm using the Libellium Module
[19:46] <DanielRichman> hangon one sec...
[19:46] <DanielRichman> http://www.libelium.com/tienda/catalog/product_info.php?cPath=21&products_id=66
[19:46] <DanielRichman> comes with a card... although it's "arduino" it connects over a 6-pin ISP header
[19:46] <DanielRichman> since ISP is SPI
[19:47] <DanielRichman> and can also connect via a 7 pin header.
[19:47] <rjharrison> http://arduino.cc/blog/?p=189
[19:47] <rjharrison> DanielRichman like that one
[19:47] <DanielRichman> yes
[19:48] <DanielRichman> There are documents about interfacing it manually floating about
[19:48] <DanielRichman> there's voltage to consider, and also some sort of power stabilisation. I'm not 100% sure what's on the libellium module - haven't looked -but if you want I can try and reverse-engineer its schematic
[19:49] <DanielRichman> Do you compile with gcc?
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[19:52] <Laurenceb> you want to use some resistors on the spi
[19:52] <Laurenceb> to avoid frying anything
[19:52] <Laurenceb> http://www.wired.com/autopia/2009/07/bob-maddox-pulse-jet/
[19:55] <kornholi> hei hei
[19:56] <Laurenceb> http://www.wired.com/autopia/2009/07/espyder/
[19:56] <rjharrison> DanielRichman yep I do compile with gcc
[19:56] <DanielRichman> -O2 or -Os?
[20:02] <rjharrison> Humm good question
[20:04] <Laurenceb> http://yuneeccouk.site.securepod.com/Aircraft.html
[20:08] <DanielRichman> "and with only 2 main moving parts in the motor (the bearings) the reliability and maintenance are like nothing seen before.!"
[20:09] <DanielRichman> hangon...
[20:09] <DanielRichman> how do you steer?
[20:09] <DanielRichman> and what about the wheels, surely they move
[20:10] Action: jcoxon is having fun hysplit trajectories
[20:10] <jcoxon> launch from falklands and you'll make it half way around the world in 72hrs
[20:10] <Laurenceb> jcoxon: going ahead with the trans?
[20:10] <Laurenceb> lol
[20:12] <jcoxon> i've been fusing cusf predict with hysplit
[20:12] <Laurenceb> did you get the ballast working?
[20:12] <jcoxon> didn't have time
[20:12] Action: Laurenceb forgot what the plan was
[20:12] <jcoxon> i'm not around to work on it till october
[20:12] <Laurenceb> I sent you the level sensor didnt I
[20:12] <jcoxon> yes
[20:12] <jcoxon> i have it still
[20:12] <Laurenceb> and natrium was going to launch?
[20:12] <jcoxon> it'll be a while before we launch
[20:13] <Laurenceb> ok
[20:13] <jcoxon> and i'm off away soon
[20:15] <Laurenceb> http://eludium.stensat.org.nyud.net/ANDE/Castor.html <- atmegas in orbit !
[20:16] <jcoxon> :-D
[20:17] <DanielRichman> nice
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[20:51] <Laurenceb> http://www.psicorp.com/publications/PDF/sr-1228.pdf
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[20:53] <Laurenceb> hi RocketBoy
[20:59] <RocketBoy> hiya
[20:59] <RocketBoy> anything new with U
[20:59] <RocketBoy> ?
[21:00] <Laurenceb> can I ask you a question about the cesaroni motors? and chance you could measure the throat diameter and exit diameter of the nozzle for me?
[21:00] <Laurenceb> I was trying to work out how far you can increase the ISP
[21:01] <Laurenceb> but not sure of the expansion ration on the stock nozzle
[21:01] <Laurenceb> bleh *ratio
[21:03] <RocketBoy> all of my motors are in store with someone else at the mo - while I sort the licence out
[21:03] <Laurenceb> ah nvm then
[21:03] <Laurenceb> I think its about 6 or so
[21:03] <Laurenceb> - the expansion ratio, sound about right?
[21:04] <RocketBoy> I have a used nozzel - but its a bit erroded
[21:04] <Laurenceb> is it graphite?
[21:04] <RocketBoy> nope - its an ablating composite I think
[21:05] <Laurenceb> interesting
[21:05] <Laurenceb> guess the burn time is so short and also dry mass isnt a serious concern
[21:05] <RocketBoy> I can take a photo or 2 of the used nozzel if its any help
[21:05] <Laurenceb> yeah thanks
[21:05] <Laurenceb> have you got anything for scale?
[21:06] <RocketBoy> sure - give me a few mins and I'll wack it up on image bin
[21:06] <Laurenceb> hopefully I can work backwards using the test data off the website
[21:06] <Laurenceb> thanks :D
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[21:36] <RocketBoy> http://imagebin.org/57991
[21:37] <Laurenceb> thanks
[21:37] <RocketBoy> http://imagebin.org/57992
[21:37] <Laurenceb> so the inside is the nozzle
[21:37] <Laurenceb> ah ok
[21:37] <RocketBoy> http://imagebin.org/57993
[21:38] <Laurenceb> so about 10 times expansion
[21:38] <RocketBoy> the nozzel exit is about 14.5mm
[21:38] <RocketBoy> the throat is 5.5
[21:38] <Laurenceb> wow small
[21:39] <Laurenceb> which motor would that be used with?
[21:39] <RocketBoy> and the entrance is 25
[21:39] <Laurenceb> oh 7 times ok
[21:39] <RocketBoy> this would be a J330 methinks
[21:40] <Laurenceb> is it a conical nozzle or bell?
[21:41] <RocketBoy> the exit is conical and the entrance looks bell
[21:41] <Laurenceb> odd
[21:41] <RocketBoy> total length is 25mm
[21:41] <Laurenceb> maybe the effect of ablation on the enternce
[21:42] <Laurenceb> well thanks for the info
[21:42] <RocketBoy> exit length is about 13mm
[21:43] <RocketBoy> entrance length about 4mm
[21:44] <RocketBoy> throat length therfore about 5mm
[21:45] <RocketBoy> that doesn't quite add up - the lengths are difficult to measure
[21:45] <Laurenceb> hmm quite high chamber pressure
[21:45] <Laurenceb> up to 10MPa
[21:45] <Laurenceb> if I've worked it out correctly
[21:46] <RocketBoy> acutally its doesn't look to bad - I suspect all that happens is the throat gets a bit wider
[21:46] <Laurenceb> I can only find the J295 on the site
[21:46] <RocketBoy> http://pro38.com/motor/J330-16A.html
[21:47] <Laurenceb> oh wow fast burner
[21:48] <RocketBoy> reasonably - its a "classic" propellant type
[21:48] <Laurenceb> hmm ok I get about 9Mpa max
[21:48] <RocketBoy> the "blue streak" is faster
[21:48] <Laurenceb> but its a fast buriner
[21:48] <Laurenceb> the 4.5 second burn time motors are going to be lower
[21:49] <RocketBoy> sure
[21:49] <Laurenceb> very roughly something like "
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[21:49] <Laurenceb> bleh 2
[21:49] <Laurenceb> thats good :P
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[21:50] <Laurenceb> looking at space motor data the performance seems to match quite well with standard AP/Al/HTBT propellant
[21:51] <Laurenceb> so with a large expansion ratio you could easily get 260 or so vacuum- some motors with huge nozzles have got 300seconds
[21:54] <Laurenceb> that J330 test is about 205seconds
[21:54] <Laurenceb> I'm guessing their test area is near sea level
[21:55] <rjharrison> RocketBoy: I have pressure sensor connected to ADC and it gives values 43-191 the range is 0 to 3.97kpa. The values are linear therefor y=mx+c Solving for max and min give m as 26.666 and c as -1173.3
[21:55] <rjharrison> This is my dubious thinking just wondered if you concur
[21:56] <rjharrison> I assume I can calibrate in this way
[21:56] <Laurenceb> ideally you want to calibrate
[21:56] <Laurenceb> use some tube with water
[21:56] <Laurenceb> then a U shaped siphon
[21:57] <rjharrison> I have using the 0 and max values of the sensor
[21:57] <Laurenceb> from the datasheet?
[21:57] <rjharrison> Yep :)
[21:57] <Laurenceb> hmm they vary a lot
[21:57] <Laurenceb> and age ect
[21:57] <RocketBoy> that will give you an idea
[21:57] <rjharrison> only at it must be a 0 at start
[21:58] <Laurenceb> but rather rough - obviously depending of the sensor quality
[21:58] <rjharrison> diff p sensor
[21:58] <rjharrison> and the max value is 3.92 kpa
[21:58] <Laurenceb> you can use two bottles
[21:58] <rjharrison> go on
[21:59] <Laurenceb> erm water... hard to explain
[21:59] <rjharrison> how do I get a known pressure
[21:59] Action: Laurenceb watching have I got news for you
[21:59] <Laurenceb> head difference
[21:59] <rjharrison> ok
[21:59] <rjharrison> I can go with that
[21:59] <rjharrison> I'll do a test
[21:59] <Laurenceb> then stick all the data in gnuplot
[21:59] <Laurenceb> and fit a polynomial
[22:00] <rjharrison> Humm
[22:00] <Laurenceb> then I'd maybe do a lookup table or something
[22:00] <Laurenceb> or floating point if you have flash to burn
[22:00] <rjharrison> A'level math 19 years ago
[22:00] <Laurenceb> heh
[22:00] <DanielRichman> Why, do you need to know the pressure on the flight computer?
[22:01] <DanielRichman> can't you just send the ADC value down in telemetry and calculate on the ground
[22:01] <RocketBoy> 1Kpa = 102mm of head
[22:01] <rjharrison> Diff between atmos and baloon
[22:01] <Laurenceb> http://bainite.wordpress.com/2008/07/26/fitting-polynomial-equations-with-gnuplot/
[22:01] <rjharrison> related to density and float
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[22:01] <rjharrison> Laurenceb thanks I think
[22:01] <RocketBoy> so 3.9 = 397mm
[22:03] <rjharrison> http://www.farnell.com/datasheets/9718.pdf
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[22:03] <rjharrison> This is the sensor Laurenceb
[22:03] <Laurenceb> I've used similar
[22:03] <rjharrison> Given that we're only interested in the relative difference if there is a slight error I'm sure it won't be too bad
[22:03] <Laurenceb> they tend to age and drift after power on
[22:04] <Laurenceb> yeah
[22:04] <rjharrison> If i'm like .05 of kpa out well who cares
[22:05] <rjharrison> The temp may play havoc any how as they are meant to op in 0-85c
[22:05] <Laurenceb> yeah that too
[22:06] <Laurenceb> it'll certainly be interesting
[22:06] <rjharrison> I have done a short video of the test system
[22:06] <rjharrison> Just uloading to flickr
[22:06] <rjharrison> RocketBoy Thanks for all your help with the dividers and caps
[22:07] <RocketBoy> np
[22:07] <rjharrison> uload is at 71% about another 30mins
[22:07] <rjharrison> 320mb on crap connection
[22:07] <rjharrison> I'm hoping for more speed at the next house
[22:08] <rjharrison> It's fun with the oscilloscope attached
[22:10] <SpeedEvil> ?
[22:10] <SpeedEvil> DSL?
[22:10] Action: SpeedEvil currently has a fault open with my ISP.
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[22:10] <SpeedEvil> Both DSL lines are falling over from around 11PM-2AM - for around half an hour in this window most nights.
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[22:11] <SpeedEvil> Hence me having a IP profile of 160kbps ATM.
[22:11] <Laurenceb> lol have I got news for you is brilliant
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[22:32] <RocketBoy> did anyone get ballasthalo2 back yet?
[22:42] <rjharrison> rjharrison not yet :)
[22:43] <rjharrison> It's on my list of things to do
[22:43] <rjharrison> BTW I just got the keys for the new house yesterday
[22:43] <rjharrison> 99%
[22:44] <RocketBoy> 99% ?
[22:44] <rjharrison> My dif pres demo
[22:44] <rjharrison> video
[22:44] <RocketBoy> Ah
[22:44] <rjharrison> It's not going to win any awards
[22:44] <rjharrison> But I thought you all might be interested
[22:45] <rjharrison> or at least humor me
[22:46] <rjharrison> should I be using the 10bits or just the most significant 8 bits on the adc
[22:46] <rjharrison> I guess 10 will give greater granularity
[22:47] <RocketBoy> use all the bits if you have them
[22:47] <rjharrison> I think there is a way to get the other 2 bits
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[22:47] <rjharrison> I'll have to look at how to add them to the 8 bits
[22:48] <rjharrison> I think int is 16bits
[22:48] <rjharrison> so i guess just pump the bits to the first 10 places
[22:49] <rjharrison> I'm going to do burst balloon tomorrow and a delfating one
[22:49] <rjharrison> The pressure profile is quite interesting
[22:49] <rjharrison> at small dia high then low and then high towards burst
[22:50] <rjharrison> You did this a while back rjharrison
[22:50] <rjharrison> opps RocketBoy
[22:52] <RocketBoy> I tested a big party balloon - yes
[22:54] <rjharrison> What did you use to measure the pressure
[22:56] <RocketBoy> a water column
[22:56] <RocketBoy> manomiter
[22:56] <RocketBoy> manoneter
[22:57] <rjharrison> Cool
[22:57] <rjharrison> So no values just pressure change
[22:59] <rjharrison> bloody long 99%
[23:00] <rjharrison> Perhaps it's doing the video conversion
[23:00] <rjharrison> 320 megs
[23:01] <RocketBoy> humm - UK gas pressure should be 18 - 20mbar - enough to fill and burst a met balloon methinks - an interesting experiment
[23:02] <RocketBoy> but not really enough to fill a party balloon acording to my tests
[23:02] <RocketBoy> ;-(
[23:05] <rjharrison> http://www.flickr.com/photos/30721501@N05/3778436727/
[23:05] <rjharrison> Sorry about the audio
[23:07] <rjharrison> Opps it's not quite finished converting yoet
[23:07] <rjharrison> yet
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[23:26] <djellison> Point, laugh, enjoy and go crazy, Ed and Fergus's talk at AmsatUK is online. http://www.batc.tv/channel.php?ch=1
[23:26] <jcoxon> hey djellison
[23:35] <RocketBoy> rjharrision - interesting video - are the variations in value (looks like 44 to 48 or so on the screen) sensor noise?
[23:35] <rjharrison> 44 43
[23:35] <rjharrison> yep
[23:35] <rjharrison> need to up the 470 to 10nf
[23:35] <RocketBoy> aaaaaaaaaaaaaaaaggggggggggggggggg
[23:36] <RocketBoy> you havn't done that yet?
[23:36] <rjharrison> http://www.flickr.com/photos/30721501@N05/3779374472/
[23:36] <rjharrison> no
[23:37] <rjharrison> Is that bad
[23:37] <rjharrison> The new link has the whole video
[23:38] <RocketBoy> say BTW guys - checkout Focus Magazine this month (August) - page 48 to 51
[23:38] <RocketBoy> tis the stuff I did for the BBC
[23:47] <rjharrison> http://www.robertharrison.org/files/ptest/ptest.wmv
[23:48] <rjharrison> Right this is the video flickr has a 1.5 min limit
[23:48] <rjharrison> even for pro
[23:48] <rjharrison> hey ho
[23:48] <rjharrison> This video actually shows the sensor working
[23:49] <rjharrison> RocketBoy Where do we get forbes form
[23:49] <rjharrison> ooh focus even
[23:51] <rjharrison> Right bed calls
[23:51] <rjharrison> I'll fix the cap tomorrow steve
[23:52] <rjharrison> Be interesting to see if it fixes the jumping between 43 & 44
[23:52] <RocketBoy> cool
[23:53] <rjharrison> Nights all
[23:53] <rjharrison> have fun and don't stay up too late... As if ...
[23:53] <RocketBoy> nights
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